1. The diagram below shows part of a molecule of deoxyribonucleic

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1.
The diagram below shows part of a molecule of deoxyribonucleic acid (DNA).
C
D
B
A
(a)
Name A, B, C and D.
A ................................................................................................................................
B ................................................................................................................................
C ................................................................................................................................
D ................................................................................................................................
(4)
(b)
Analysis of a molecule of DNA showed that cytosine accounted for 42 per cent of the
content of the nitrogenous bases. Calculate the percentage of bases in the molecule which
would be thymine. Show your working.
Answer...............................................
(3)
(c)
During the process of transcription, one of the DNA strands is used as a template for the
formation of a complementary strand of messenger RNA (mRNA). The diagram below
shows the sequence of bases in part of a strand of DNA.
DNA
G
C
G
T
C
A
T
G
C
mRNA
1
(i)
Write the letters of the complementary bases in the boxes of the mRNA strand.
(2)
(ii)
How many amino acids are coded for by this part of the strand of mRNA?
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(1)
(Total 10 marks)
2.
Describe the role of messenger RNA (mRNA) in the following processes.
(a)
Transcription
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(3)
(b)
Translation
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(3)
(Total 6 marks)
2
3.
The diagram below represents the structure of a transfer RNA (tRNA) molecule. Transfer RNA
has a similar structure to messenger RNA (mRNA), but the single strand of nucleotides is
folded back on itself. The folds are held in place by base pairing.
B
G G A A
A
Amino
acid
(a)
List the four bases in the region labelled A which pair with those already shown.
.....................................................................................................................................
(1)
(b)
The three shaded bases in region B are responsible for binding to an mRNA molecule
during translation. Give the name used to describe this group of three bases on the tRNA.
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(1)
3
(c)
Each amino acid is coded for by three bases on the mRNA molecule. Explain why a
group of three bases is the smallest number that can be used to code for all of the amino
acids found in proteins.
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(3)
(d)
The particular amino acid bound to a tRNA molecule depends on the three bases at
position B. Explain why this is important during the translation of mRNA to form a
polypeptide.
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(2)
4
(e)
In an experiment to investigate the role of tRNA in the synthesis of proteins, cells were
exposed for a brief time to radioactively labelled amino acids. Samples of the cells were
then removed at intervals over a period of 20 minutes, and the level of radioactivity
associated with tRNA and protein was measured as counts per minute (cpm).
The graph below shows the results of the experiment.
350 –
Protein
Level of
radioactivity
/cpm
300 –
250 –
200 –
150 –
100 –
tRNA
50 –
–
–
–
(i)
–
–
0–
0
5
10
15
20
Describe the results shown in the graph.
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5
(ii)
Suggest an explanation for the changes in radioactivity found in protein over the
first five minutes.
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(2)
(Total 12 marks)
4.
The diagram below shows a stage in the process of translation during protein synthesis. This
process is occurring on a ribosome.
Amino acids
Ribosome
Amino acid
4
tRNA molecule
1
2
3
Anticodon
GU A
GGU
AAA
G C C AC G
GG
U
Part of a messenger
RNA molecule
6
(a)
Describe the structure of a ribosome.
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(2)
(b)
The table below shows the anticodons of some tRNA molecules and the specific amino
acids that each one carries.
tRNA anticodon
Amino acid
GGU
Proline
CCA
Glycine
AAA
Phenylalanine
CGA
Alanine
ACC
Tryptophan
UUU
Lysine
Using the information in the table, identify amino acids 2 and 3 shown in the diagram on
the previous page.
Amino acid 2 .........................................................................................................................
Amino acid 3 .........................................................................................................................
(2)
7
(c)
During translation, amino acids are linked by a peptide bond.
(i)
Draw a diagram to show two amino acids linked by a peptide bond.
(3)
(ii)
Name the type of reaction that occurs during the formation of a peptide bond.
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(1)
(Total 8 marks)
5.
Protein synthesis involves transcription and translation.
(a)
(i)
Where does transcription take place in a eukaryotic cell?
………………………………………………………………………………………
(1)
(ii)
Name the type of chemical reaction that occurs when a strand of messenger RNA is
formed from individual nucleotides.
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(1)
8
(b)
The diagram below shows part of a messenger RNA (mRNA) molecule.
C
(i)
G
A
A
C
C
G
C
C
C
G
A
A
U
C
A
C
C
What is the maximum number of amino acids coded for by this strand of mRNA?
.....................................................................................................................................
(1)
(ii)
Complete the diagram below to show the sequence of bases on the strand of DNA
that coded for this mRNA.
(2)
(c)
A strand of mRNA was found to have 53 codons but the protein produced from it
contained only 51 amino acids. Suggest two reasons for this difference.
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(2)
9
(d)
Describe the process of translation.
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(5)
(Total 12 marks)
10
6.
During the process of protein synthesis in cells, the ribosome acts as a kind of ‘workbench’
where protein molecules are constructed.
The diagram below shows a protein being formed on a ribosome.
(a)
Name the following structures shown on the diagram.
P ..................................................................................................................................
Q ..................................................................................................................................
R ..................................................................................................................................
S ..................................................................................................................................
(4)
11
(b)
Complete the following passage describing the process of protein synthesis by writing
Leave the appropriate word in each space. blank
Genetic information is stored in the nucleus of a cell as molecules of
................................................ . Protein synthesis occurs in the cytoplasm. Genetic
information is first copied in the process of ................................................ , then leaves
the nucleus in the form of molecules of ................................................ .
In the cytoplasm these molecules pass to ribosomes to begin the process of
................................................ . At the ‘workbench’ on the ribosome
................................................ base pairing occurs. Adenine pairs with
................................................ and cytosine pairs with ................................................ .
Adjacent amino acids are joined together by ................................................ bonds.
(4)
(Total 8 marks)
7.
The diagram below shows part of a molecule of messenger RNA.
G
(a)
A
U
C
G
U
G
On the diagram, draw a ring around a mononucleotide and label it with the letter M.
(1)
12
(b)
Messenger RNA is formed during protein synthesis by a process called transcription.
Describe the events which occur during transcription.
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(5)
(c)
During translation, transfer RNA molecules line up against the messenger RNA molecule.
The diagram below shows the structure of one transfer RNA molecule.
A
(i)
G
C
State precisely where in the cell translation takes place.
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(1)
(ii)
On the diagram of the messenger RNA molecule above, draw a ring around the
codon that this transfer RNA molecule would bind to. Label it with the letter C.
(1)
(Total 8 marks)
13
8.
The function of a protein depends on its shape.
(a)
(i)
Explain what is meant by the primary structure of a protein.
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(1)
(ii)
Explain how the primary structure of a protein is important in determining its
shape.
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(2)
(b)
Explain why most enzymes are specific to only one substrate.
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(2)
14
(c)
Describe the process that converts a genetic sequence on messenger RNA into the
primary sequence of a protein.
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(4)
(Total 9 marks)
15
9.
Proteins have a wide range of functions in living organisms. The function of a protein is related
to its precise three dimensional shape, which is determined by its specific sequence of amino
acids. The diagram below shows a model of a typical protein molecule.
(a)
(i)
Complete the diagram below to give the structure of the amino acid glycine.
H
C
H
(2)
16
(ii)
Explain how a specific sequence of amino acids can form the precise three
dimensional shape of a protein molecule.
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(3)
(b)
The following DNA base sequence codes for part of a protein molecule.
TACGGTATGCCAACCTTC
(i)
State the number of amino acids coded by this section of DNA.
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(1)
(ii)
Name the process involved in converting a base sequence of DNA into a base
sequence of messenger RNA (mRNA).
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(1)
(iii)
Give the complementary mRNA sequence to the DNA sequence above.
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(2)
(Total 9 marks)
17
10.
(a)
The diagram below shows the structure of a mononucleotide from a DNA molecule.
A
B
Name the parts of the mononucleotide labelled A and B.
A ..............................................
B ..............................................
(1)
(b)
The table below shows the percentage of different bases present in the DNA from two
organisms.
Percentage of each base present
Organism
Yeast
Cow
(i)
Adenine
Guanine
Thymine
Cytosine
31
19
31
19
29
Complete the table to show the percentage of adenine, guanine and cytosine in the
DNA of a cow.
(1)
18
(ii)
Explain how you worked out the percentage of guanine present in the DNA of a
cow.
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(3)
(c)
DNA and messenger RNA (mRNA) have different properties. DNA is very stable but
mRNA breaks down quickly and most of it will be broken down within a day of it being
produced. Suggest why it is important for DNA to be more stable than mRNA.
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(2)
19
(d)
Protein synthesis involves transcription and translation. Describe the process of
transcription.
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(5)
(Total 12 marks)
11.
The diagram below shows some cell structures involved in protein synthesis in eukaryotic cells.
Nucleus
Rough endoplasmic reticulum
20
(a)
Describe the events that occur inside the nucleus to produce a molecule of messenger
RNA (mRNA).
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(4)
(b)
Describe the role of the ribosomes in protein synthesis.
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(3)
21
(c)
The table below gives some of the base triplets on DNA that code for some amino acids
and stop signals.
Base triplet on DNA
Amino acid / stop signal
CCC
Glycine
AAA or AAG
Phenylalanine
AGA or AGC
Serine
GCG
Arginine
TTT
Lysine
ATT or ATC or ACT
Stop signal
The diagram below shows the five base triplets of a gene, labelled T1 to T5, and the
complementary messenger RNA (mRNA).
The sequence of amino acids at the end of the protein produced is also shown.
Last part of the
DNA strand:
T1
T2
T3
T4
CCC
GCG
AG C
TTT
T5
Complementary
mRNA:
Amino acid
sequence:
(i)
Glycine
–
–
–
Write in the codons found on the mRNA complementary to the base triplets T1,
T2, T3 and T4 on the diagram above.
(2)
(ii)
Using the information in the table, complete the amino acid sequence shown in the
diagram above. The first one has been done for you.
(2)
22
(iii)
Use the information in the table to suggest a base triplet for T5, on the DNA
molecule.
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(1)
(Total 12 marks)
12.
Some cells from the small intestine were placed in a solution containing amino acids. The
diagram below shows the movement of these amino acids over a 15 minute period.
Amino acids move through the cell surface
membrane into the cells
Amino acids found in the cytoplasm of the cells
Amino acids found at ribosomes where they are
joined together to form protein
(a)
(i)
Name two mechanisms by which amino acids can move through the cell surface
membrane.
1 ........................................................................................................................
2 ........................................................................................................................
(2)
(ii)
Name the stage of protein synthesis that occurs at the ribosomes.
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(1)
23
(b)
(i)
If a protein formed at a ribosome is 300 amino acids long, state how many water
molecules would be released during its synthesis.
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(1)
(ii)
Assuming that the start codon on mRNA is three bases long and the stop codon is
also three bases long, calculate the minimum number of bases in the mRNA needed
to code for a protein that is 300 amino acids long.
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(1)
(c)
Suggest two molecules, other than amino acids and water, that may be found at the
ribosomes and that are involved in protein synthesis.
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(2)
(Total 7 marks)
13.
The diagram below shows part of a DNA molecule.
Y
Z
X
Adenine
W
Cytosine
24
(a)
(i)
Name the parts of the molecule represented by each of the following letters.
W ......................................................................................................................
X ......................................................................................................................
Y ......................................................................................................................
Z ......................................................................................................................
(4)
(ii)
Name the type of bond that holds the two strands of DNA together.
...........................................................................................................................
(1)
(b)
The table below shows the amino acids coded by mRNA codons.
Second base
C
A
G
UUU
U UUC
UUA
UUG
Phenylalanine
Phenylalanine
Leucine
Leucine
UCU
UCC
UCA
UCG
Serine
Serine
Serine
Serine
UAU
UAC
UAA
UAG
Tyrosine
Tyrosine
Stop
Stop
UGU
UGC
UGA
UGG
Cysteine
Cysteine
Stop
Tryptophan
U
C
A
G
CUU
CUC
C CUA
CUG
Leucine
Leucine
Leucine
Leucine
CCU
CCC
CCA
CCG
Proline
Proline
Proline
Proline
CAU
CAC
CAA
CAG
Histidine
Histidine
Glutamine
Glutamine
CGU
CGC
CGA
CGG
Arginine
Arginine
Arginine
Arginine
U
C
A
G
AUU
A AUC
AUA
AUG
Isoleucine
Isoleucine
Isoleucine
Methionine
ACU
ACC
ACA
ACG
Threonine
Threonine
Threonine
Threonine
AAU
AAC
AAA
AAG
Asparagine
Asparagine
Lysine
Lysine
AGU
AGC
AGA
AGG
Serine
Serine
Arginine
Arginine
U
C
A
G
GUU
GUC
G GUA
GUG
Valine
Valine
Valine
Valine
GCU
GCC
GCA
GCG
Alanine
Alanine
Alanine
Alanine
GAU
GAC
GAA
GAG
Aspartic acid
Aspartic acid
Glutamic acid
Glutamic acid
GGU
GGC
GGA
GGG
Glycine
Glycine
Glycine
Glycine
U
C
A
G
(i)
Third base
First base
U
Name the process by which mRNA is formed in the nucleus.
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(1)
25
(ii)
Reading from left to right, what is the sequence of amino acids coded by the
following length of mRNA?
G
A
U
C
G
U
U
G
U
A
A
G
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(1)
(iii)
A mutation occurred so that the base cytosine was replaced by guanine in this
mRNA. Using the information in the table, explain why this mutation could affect
the tertiary structure of the protein formed from this mRNA.
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(3)
(Total 10 marks)
14.
(a)
The statements in the table below refer to three biological molecules.
If a statement is correct place a tick ( ) in the appropriate box and if a statement is
incorrect place a cross ( ) in the appropriate box. Four boxes have already been
completed for you.
Statement
Starch
Glycogen
Monosaccharide
Is a polymer
Glycosidic
bonds are
present
Is an energy
store in
animal cells
Has high
solubility in
water
(4)
26
(b)
The diagram below represents a polypeptide consisting of amino acids.
State the minimum number of bases needed to code for this polypeptide along a strand of
mRNA.
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(1)
(c)
Describe the key stages involved in protein synthesis, from the genetic code in the
nucleus to the sequence of amino acids being assembled at the ribosome.
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(5)
27
(d)
Explain how the sequence of amino acids determines the shape of a protein.
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(2)
(Total 12 marks)
15.
The diagram below summarises the steps involved in the semi-conservative replication of DNA.
Double strand of DNA
Step 1
Enzyme A
Two strands separated
Step 2
Complementary nucleotides line up against each strand
Step 3
Enzyme B
Nucleotides join to form two new polynucleotide chains
Step 4
Two identical DNA molecules formed
(a)
Describe how Enzyme A separates the two DNA strands in Step 1.
……………………………………………….………………………………………
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(1)
28
(b)
In Step 3 the individual nueleotides are joined up to form a polynucleotide chain by
Enzyme B.
Name the type of reaction that Enzyme B catalyses.
……………………………………………….………………………………………
(1)
(c)
Give the phase of the cell cycle during which DNA replication occurs.
……………………………………………….………………………………………
(1)
(Total 3 marks)
16.
(a)
Protein synthesis involves the process of transcription followed by translation. The
diagram below shows part of a messenger RNA (mRNA) molecule. It shows a sequence
of seven bases.
G
(i)
A
U
C
G
U
G
Name the pyrimidine bases shown in this sequence.
...........................................................................................................................
(1)
(ii)
Write down the sequence of bases on the strand of DNA that coded for this
messenger RNA.
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(1)
29
(b)
In some prokaryotic cells, the production of mRNA during transcription can occur at a
rate of 50 bases per second. Calculate how long it would take to produce a mRNA
molecule that coded for a protein containing 200 amino acids. Show your working.
Answer ....................................
(3)
30
(c)
Describe the process of translation.
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(5)
(d)
In prokaryotic cells, a molecule of mRNA can be translated as soon as it is made.
Suggest an explanation for this.
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(2)
(Total 12 marks)
31
17.
(a)
The diagram below shows a nucleotide with a nitrogenous base found in RNA but not
DNA.
E
OH
O
OH
P
O
H2C
O
C
H
F
C
H
H
C
C
OH
OH
H
H
C
C
C
N
H
C
O
N
O
H
G
(i)
Name the molecules labelled E, F and G.
E .........................................
F .........................................
G ........................................
(3)
(ii)
Name the part of the cell where RNA nucleotides are combined to form strands of
messenger RNA (mRNA).
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(1)
32
(b)
The table below shows which amino acids are coded for by different codons on mRNA.
First position
(i)
Second position
Third position
U
C
A
G
U
phe
phe
leu
leu
ser
ser
ser
ser
tyr
tyr
Stop
Stop
cys
cys
Stop
trp
U
C
A
G
C
leu
leu
leu
leu
pro
pro
pro
pro
his
his
gln
gln
arg
arg
arg
arg
U
C
A
G
A
ile
ile
ile
met
thr
thr
thr
thr
asn
asn
lys
lys
ser
ser
arg
arg
U
C
A
G
G
val
val
val
val
ala
ala
ala
ala
asp
asp
glu
glu
gly
gly
gly
gly
U
C
A
G
The letters below represent a section of mRNA coding for the enzyme RNA
polymerase. Using the table, give the amino acid sequence coded for by this
mRNA sequence.
UACGUGGAAAGA
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(2)
(ii)
Name the process that converts the mRNA sequence into a sequence of amino
acids.
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(1)
(Total 7 marks)
33
18.
Lactose is a sugar found in human milk.
(a)
Lactose is a disaccharide that can be hydrolysed to its two monosaccharides, galactose
and glucose.
(i)
The diagram below shows lactose being hydrolysed. Complete the diagram by
drawing the missing components of the monosaccharide galactose in the left-hand
box and the monosaccharide glucose in the right-hand box.
Lactose
CH 2 OH
HO
CH 2 OH
O
H
H
O
H
H
O
H
OH
H
H
OH
CH 2 OH
H
OH
H
H
OH
OH
CH 2 OH
O
Galactose
O
Glucose
(2)
(ii)
Explain the term hydrolysis.
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(2)
34
(b)
Galactosaemia is a rare and potentially serious inherited condition. It is caused by a
recessive allele that reduces the ability of the body to break down galactose.
A couple is expecting a second child. Neither parent has galactosaemia but their first
child does have galactosaemia.
(i)
Using the symbols G and g, complete the genetic diagram below to show the
probability of the couple’s second child not having galactosaemia.
Parents’ genotypes ..........................................
..........................................
Parents’ gametes
Possible genotypes
of second child
..................
..................
..................
..................
Probability of their second child not having galactosaemia .............................
(3)
(ii)
The couple wanted confirmation that their second unborn child did not have
galactosaemia. To do this, fetal cells were taken, the DNA extracted and the alleles
associated with galactosaemia were sequenced.
A mutation was found in one of these alleles but the protein produced by this allele
was the same as the protein produced by the normal allele. The couple were told
this could be explained by the degenerate nature of the genetic code.
Explain how the degenerate nature of the genetic code could allow the mutated
allele to produce the same protein as a normal allele.
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(2)
35
(iii)
Outline the ethical issues related to genetic screening of a fetus for inherited
disorders such as galactosaemia.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
(Total 12 marks)
19.
Amino acids are coded for by one or more DNA triplet codons. The table below shows some
amino acids found in human proteins and their corresponding DNA triplet codons.
A DNA triplet codon for the stop signal is also shown.
Amino acid
Triplet codons
Threonine
TGA TGG TGT
Glutamine
GTT GTC
Glycine
CCA CCG CCT CCC
Arginine
TCT
Alanine
CGG CGC
Stop signal
ACT
The diagram below shows part of a DNA molecule. This part of the DNA molecule is located
near the end of a gene.
codon 47
T
C
T
codon 48
C
G
codon 49
G
T
G
G
codon 50
G
T
codon 51
C
C
C
A
36
(a)
Give the sequence of amino acids found in the polypeptide chain that is coded for by this
part of the DNA strand.
.....................................................................................................................................
.....................................................................................................................................
(2)
(b)
Give the next triplet codon that you would expect to see on this DNA strand if codon 51
coded for the last amino acid in the polypeptide chain.
.....................................................................................................................................
(1)
(c)
Complete the diagram below to show the sequence of bases on a molecule of messenger
RNA synthesised from this part of the DNA strand.
(2)
(d)
Mutations can occur during DNA replication.
(i)
Suggest what would happen to the structure of the protein coded for by this DNA
molecule if thymine in codon 49 were replaced by cytosine.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
37
(ii)
Suggest what would happen to the structure of the protein coded for by this DNA
molecule if adenine replaced the first thymine in codon 47.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(Total 9 marks)
20.
Urease is an enzyme which catalyses the breakdown of urea to ammonia and carbon dioxide.
An experiment was carried out into the effect of pH on the activity of urease. 10 cm3 of pH 3
buffer solution was mixed with 1 cm3 of urease solution. This mixture was then added to
10 cm3 of urea solution and the concentration of ammonia in the mixture was measured after 60
minutes. This procedure was repeated using buffer solutions of pH 4, 5, 6, 7, 8 and 9.
The results are shown in the graph below.
100
80
60
Concentration
of ammonia/
arbitrary units
40
20
0
3
4
5
6
7
8
9
pH
38
(a)
What do these results suggest is the optimum pH for urease activity?
....................................................................................................................................
(1)
(b)
Suggest how the experiment could be modified to determine the optimum pH more
accurately.
....................................................................................................................................
....................................................................................................................................
(1)
(c)
Explain why no ammonia was produced at pH 3.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
(d)
Explain why less ammonia is produced at pH 9 than at pH 8.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(e)
Describe how this experiment could be modified to determine the effect of enzyme
concentration on the activity of urease.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(4)
(Total 11 marks)
39
21.
The graph below shows the results of an investigation into the effect of substrate concentration
on the initial rate of an enzyme-controlled reaction.
0.20
B
C
Initial
0.15
rate of
reaction
/ mg of
products s –1
0.10
0.05
A
0
0
(a)
10
20
30
40
Substrate concentration / mg cm –3
50
60
Suggest two conditions, apart from temperature, that should be kept constant in this
investigation.
1 .................................................................................................................................
2 .................................................................................................................................
(2)
(b)
Explain why changes in the substrate concentration cause an increase in the rate of
reaction between points A and B on the graph.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
40
(c)
Suggest why the curve levels off between points B and C.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(d)
On the graph on page 6, sketch a curve to show how the results for the investigation
would change if it were repeated at a lower temperature.
Explain any differences between the two curves.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
(Total 9 marks)
22.
Read through the following passage about enzymes, then write on the dotted lines the most
appropriate word or words to complete the passage.
Enzymes can be described as biological .............................................. as they reduce
the .......................................... needed for a metabolic reaction to occur.
The ........................................... combines with the enzyme at a specific region of
the molecule called the ........................................ . The shape of this region can
be altered by a change in pH or ................................................ which will
............................................... the rate of the metabolic reaction.
(Total 6 marks)
41
23.
The graph below shows the results of an experiment to investigate the effect of amylase Leave
concentration on the rate of starch breakdown.
90
80 –
Rate of starch
breakdown
/ mg min 1
70 –
60 –
50 –
40 –
30 –
20 –
10 –
0–
0
(a)
100
50
150
200
Concentration of amylase / mg cm 3
250
Outline a procedure that could have been used to produce these results.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(4)
42
(b)
Explain the effect of amylase concentration on the rate of starch breakdown.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(c)
Suggest reasons why the points on the graph do not lie on a straight line.
(3)
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(d)
Cellulase is another enzyme that breaks the bonds between glucose molecules in a
polymer. Explain why adding this enzyme in addition to amylase would have no effect on
the rate of starch breakdown.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(Total 12 marks)
43
24.
(a)
With reference to enzyme activity, explain the meaning of the following terms:
Catalyst ................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
Activation energy ……..........................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
(4)
44
(b)
An investigation was carried out to study the effect of copper sulphate concentrations on
the breakdown of cellulose by the enzyme cellulase.
Two concentrations of copper sulphate were used.
0.01 mol dm-3
1.00 mol dm-3
Water was used as a control.
The results are shown in the graph below.
5
Water
0.01 mol dm –3
copper sulphate
Total quantity
of cellulose
4
broken down
/ arbitrary units
1.00 mol dm –3
copper sulphate
3
2
1
0
(i)
0
1
2
3
Time / days
4
5
6
Name the type of reaction that is catalysed by cellulase.
.....................................................................................................................................
(1)
(ii)
Name the bond that is broken by cellulase.
.....................................................................................................................................
(1)
45
(iii)
Using the information shown in the graph, describe the effect of copper sulphate on
the rate of breakdown of cellulose.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(iv)
Copper ions bind to cellulase and cause disulphide bonds to break.
Explain the effect of copper ions on the activity of the cellulase.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(Total 12 marks)
46
25.
Sucrose is a disaccharide made up from one molecule of glucose bonded to one molecule of
fructose. Sucrose needs to be digested by the enzyme sucrase before it can be absorbed into the
blood.
(a)
The diagram below illustrates how the enzyme sucrase may catalyse the breakdown of
sucrose into glucose and fructose.
Sucrose
R
Glucose
Fructose
Q
Sucrase
Use the diagram to identify:
(i)
reactant Q
...........................................................................................................................
(1)
(ii)
the region labelled R
...........................................................................................................................
(1)
(iii)
the name of the bond between the glucose and fructose molecules that is broken by
the reaction shown in the diagram.
...........................................................................................................................
(1)
47
(b)
(i)
Explain why sucrase will digest sucrose and not any other disaccharide.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
(ii)
Name and describe one way that glucose is absorbed across cell membranes.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(Total 8 marks)
26.
Proteins are chains of amino acids and have a wide range of functions in living organisms.
(a)
(i)
The diagram below shows part of the general structure of two different amino
acids.
Complete the diagram to show how these two amino acids can be joined together.
H
R
N—C—
H
H
R
O
—C—C
H
OH
(1)
(ii)
Name the bond that is formed between the two amino acids.
...........................................................................................................................
(1)
48
(b)
Explain how the specific sequence of amino acids in a protein determines its threedimensional structure.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(c)
Enzymes are proteins that speed up chemical reactions within living organisms. The
graph below shows the effect of changing enzyme concentration on the rate of reaction.
Rate of
reaction
X
Enzyme concentration
(i)
Explain why increasing the enzyme concentration above point X on the graph does
not increase the rate of the reaction further.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
49
(ii)
Outline the practical procedures that could have been used to obtain the results
shown on the graph.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(4)
(Total 10 marks)
27.
(a)
Describe the structure of a plant cell wall.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
50
An experiment was carried out to determine the effect of two enzymes, enzyme A and
enzyme B, on the yield of apple juice.
An apple was cut into small pieces and blended in a food processor to produce apple pulp.
Four samples of apple pulp of equal mass were mixed with various combinations of
enzyme A, enzyme B and water, as detailed in the table below. Both enzyme solutions
were at the same concentration.
Sample number
Mixture
1
Apple pulp + 5 cm3 enzyme A + 5 cm3 water
2
Apple pulp + 5 cm3 enzyme B + 5 cm3 water
3
Apple pulp + 5 cm3 enzyme A + 5 cm3 enzyme B
4
Apple pulp + 10 cm3 water
The samples were incubated at 30 °C for 15 minutes.
Each sample was then placed in a separate filter funnel and the apple juice collected into
a measuring cylinder. The volumes of the apple juice collected from each sample are
shown in the bar chart below.
40
Volume of apple juice collected / cm3
(b)
30
20
10
0
1
2
3
Sample number
4
51
(i)
Suggest why the apple pulp incubated with water only (sample 4) yielded some
apple juice.
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
Describe the effect that enzymes A and B have on the yield of apple juice in
samples 1, 2 and 3.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
52
(iii)
Suggest how these enzymes increase the yield of apple juice.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(4)
(Total 10 marks)
28.
The diagram below illustrates part of a glycogen molecule.
CH2OH
C
H
C
HO
(a)
CH2OH
O H
H
OH
H
C
C
H
OH
H C
C
C
O
CH2OH
O H
H
OH
H
C
C
H
OH
H C
C
C
O
CH2OH
O H
H
OH
H
C
C
H
OH
H C
C
C
O
CH2OH
O H
H
OH
H
C
C
H
OH
H C
C
C
O
CH2OH
O H
H
OH
H
C
C
H
OH
H C
C
C
O
O
H
OH
H
C
C
H
OH
H
C
OH
State the role of glycogen in the human body.
.....................................................................................................................................
(1)
53
(b)
An enzyme is used to break the bonds holding the monomers (glucose molecules)
together.
(i)
In the space below draw one of the monomers that would result from this reaction.
(2)
(ii)
Explain why this enzyme will not break the bonds in a protein molecule.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
(c)
Explain the advantages, to living organisms, of using enzymes in biological reactions.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(Total 8 marks)
54
29.
The enzyme pectinase can be used in the commercial process of peeling oranges. In this
process, the waxy (lipid) surface of the oranges is first removed. The oranges are then
submerged in a solution of pectinase. This enzyme hydrolyses the polysaccharide pectin that
holds the cells in the peel together.
After about 12 hours in the solution of pectinase, the orange peel falls off the oranges leaving
clean segments.
(a)
(i)
Suggest why the waxy surface of the oranges is removed before they are
submerged in pectinase.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(ii)
Explain why pectinase does not hydrolyse the cellulose found in the orange peel
cell walls.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(b)
(i)
Suggest why chopping up the oranges could speed up hydrolysis.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
55
(ii)
The pectinase shows a small increase in concentration over the 12 hours of the
hydrolysis. Suggest why the concentration of the pectinase increases slightly.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(Total 8 marks)
30.
(a)
Explain what is meant by each of the following terms.
(i)
Allele
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(ii)
Phenotype
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
56
(b)
Manx cats have no tails and have the genotype Mm. Cats with normal tails have the
genotype mm. The genotype MM is an example of a lethal genotype and the embryo
with this genotype does not develop.
In the space below, draw a genetic diagram to find the probability that a kitten produced
by crossing two Manx cats will have a normal tail.
(3)
57
(c)
Siamese cats have light-coloured fur, but with dark-coloured faces, ears, tails and paws.
This is due to a temperature-sensitive mutation. As a result of this mutation, the enzyme
responsible for the production of the pigment is easily denatured.
A Siamese cat Suggest an explanation for the distribution of dark-coloured fur in a
Siamese cat.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(Total 10 marks)
58
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