Questions on Units 3.7 on Nucleic Acids
1
The following diagram shows a DNA molecule which has been “unzipped” into two single strands.
(a) The diagram shows the DNA molecule undergoing semi-conservative replication. Explain the term
semi-conservative replication.
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(3 marks)
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(b) The same DNA molecule unzips to provide a template for mRNA. The simplified diagram below
shows the DNA molecule and the mRNA strand being produced.
DNA single strand
(i)
mRNA strand
The base sequence for part of the DNA single strand is shown below:
… G C A C T G A T A C C G T A C …
triplet 1 triplet 2 triplet 3 triplet 4 triplet 5
Complete the table below to identify the base sequence for the mRNA codon.
DNA single strand
triplet 1
triplet 2
triplet 3
triplet 4
triplet 5
G C A
C T G
A T A
C C G
T A C
mRNA codon
(2 marks)
(ii) Give the name to the specific length of the mRNA molecule.
.……………………………………………………………………………………………
(1 mark)
(iii) Complete the table below to identify the base sequence for the tRNA anticodon.
DNA single strand
triplet 1
triplet 2
triplet 3
triplet 4
triplet 5
G C A
C T G
A T A
C C G
T A C
tRNA anticodon
(2 marks)
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(c) Explain the relationship between the sequence of the DNA triplets and the structure of a protein
which is made in the ribosome.
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(5 marks)
(d) The diagram below shows the process of mRNA entering the ribosome and bonding with tRNA.
X
tRNA
mRNA
(i)
Name the process that is taking place in the diagram.
.……………………………………………………………………………………………
(1 mark)
(ii) Identify material X from the diagram.
.……………………………………………………………………………………………
(1 mark)
(iii) Name the material(s) which the ribosome is composed of.
.……………………………………………………………………………………………
(2 marks)
Total: 17 marks
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2
The diagram below shows a simple nucleotide.
A
B
C
(a) Name the parts A, B and C in the diagram.
A ……………………………………………………………………………………………….
B ……………………………………………………………………………………………….
C ……………………………………………………………………………………………….
(3 marks)
(b) Which part of the nucleotide, A, B or C, contains the element nitrogen?
.………………………………………………………………………………………………..
(1 mark)
(c) The diagram below shows eight nucleotides from a DNA double-helix molecule.
C
A
T
G
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(i)
On the diagram, fill in the blank boxes to match the nucleotides correctly.
(2 marks)
(ii) The entire DNA molecule has 24% adenine and 20% cytosine.
State the percentages for the contents of each of the following in the DNA molecule:
guanine .…………………………………… %
thymine .…………………………………… %
uracil
.…………………………………… %
(3 marks)
(d) State any two differences between DNA and RNA.
1 ……………………………………………………………………………………………….
.………………………………………………………………………………………………...
2 ……………………………………………………………………………………………….
.………………………………………………………………………………………………...
(2 marks)
Total: 11 marks
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