DNA Replication Question
Booklet
Name………………………………….…..
Target Grade…………………..
Grade achieved……………….
__/25
__%
Unit 2- Woodford County High School
1.
The diagram shows a section of a DNA molecule.
P
Q
Guanine
R
Adenine
(a)
Name parts P, Q and R.
P .................................................................................................................................
Q .................................................................................................................................
R .................................................................................................................................
(2)
(b)
Explain why DNA replication is described as semi-conservative.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(c)
A piece of DNA was analysed. 15% of its nucleotides were found to contain
guanine. What percentage of its nucleotides would you expect to contain adenine?
Show your working.
Answer ....................................
(2)
(Total 6 marks)
Unit 2- Woodford County High School
2.
The diagram shows the process of DNA replication. The horizontal lines represent the
positions of bases.
W
(i)
A
X
C
Y
X
Z
What is represented by the part of the DNA molecule labelled W?
.....................................................................................................................................
(1)
(ii)
In the diagram, A represents adenine and C represents cytosine.
Name the base found at
position X;
...................................................................................................................
position Y;
...................................................................................................................
position Z.
...................................................................................................................
(3)
(Total 4 marks)
Unit 2- Woodford County High School
3.
(a)
There are two forms of nitrogen. These different forms are called isotopes. 15N is a
heavier isotope than the normal isotope 14N.
In an investigation, a culture of bacteria was obtained in which all the nitrogen in
the DNA was of the 15N form. The bacteria (generation 0) were transferred to a
medium containing only the normal isotope, 14N, and allowed to divide once. A
sample of these bacteria (generation 1) was then removed. The DNA in the
bacteria of generation 1 was extracted and spun in a high-speed centrifuge.
The bacteria in the 14N medium were allowed to divide one more time. The DNA
was also extracted from these bacteria (generation 2) and spun in a high speed
centrifuge.
The diagram shows the results of this investigation.
Generation 0
DNA from
bacteria with
15
N only
(i)
Generation 1
DNA from
bacteria which
have divided
once in a 14N
medium
Generation 2
DNA from
bacteria which
have divided
twice in a 14 N
medium
Which part of the DNA molecule contains nitrogen?
..........................................................................................................................
(1)
(ii)
Explain why the DNA from generation 1 is found in the position shown.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
Unit 2- Woodford County High School
(iii)
Complete the diagram to show the results for generation 2.
(2)
(b)
The table shows the percentage of different bases in the DNA of different
organisms.
Organism
Adenine%
Human
Guanine%
Thymine%
Cytosine%
19
Bacterium
24
26
24
26
Virus
25
24
33
18
(i)
Complete the table to show the percentages of different bases in human
DNA.
(2)
(ii)
The structure of virus DNA is different from the DNA of the other two
organisms. Giving evidence from the table, suggest what this difference
might be.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(Total 9 marks)
Unit 2- Woodford County High School
4.
The diagram shows the replication of a molecule of DNA.
Original DNA molecule
Original strand
New strand
(a)
Explain why DNA replication is described as semi-conservative.
.....................................................................................................................................
.....................................................................................................................................
(1)
(b)
(i)
What is meant by specific base pairing?
..........................................................................................................................
..........................................................................................................................
(ii)
Explain why specific base pairing is important in DNA replication.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(3)
(c)
Describe two features of DNA which make it a stable molecule.
1 ..................................................................................................................................
.....................................................................................................................................
2 ..................................................................................................................................
.....................................................................................................................................
(2)(Total 6 marks)
Unit 2- Woodford County High School
Mark Scheme
1.
(i)
(ii)
sugar or phosphate / S-P / nucleotide chain/backbone /
original/parent DNA;
1
X thymine; Y guanine; Z adenine;
(Allow T, G and A) Reject: thiamine
3
[4]
2.
(a)
TCAG;
(b)
(i)
Nucleotide;
1
(ii)
Hydrogen bonds;
1
(c)
1
Chains part;
breaking of hydrogen bonds;
semi-conservative replication / each chain acts as a template;
nucleotides / bases line up with complementary bases;
join / polymerise;
Max 3
[6]
3.
(a)
(i)
(ii)
base / named bases;
reject nucleotide or uracil
it has been produced by semi-conservative replication / one old strand
1
and one new; one strand has 15N bases and the other 14N;
Accept light/ heavy N
(therefore) it is less dense / lighter;
2 max
(iii)
one band is in same position as generation 1;
one band higher;
accept a line. N.B. need a visible gap
(b)
2
(i)
A = 31 and JT = 31;
C = 19;
(ii)
viral DNA single-stranded / not double-stranded;
evidence from table e.g. not equal amount of A and T
/ C and G / all different;
ignore no base-pairing In this Question assume
It’ means viral DNA
2
2
[9]
4.
(a)
one strand of original molecule in each new molecule/DNA;
(b)
(i)
each base only pairs with one other/one specific base /
complementary base pairing;
example – pairing of adenine and thymine/cytosine and guanine/
purine and pyrimidine;
Unit 2- Woodford County High School
1
(ii)
(c)
identical/exact copies made;
same base sequence as original DNA;
both strands act as template/complementary base pairing
occurs on both strands;3 (max 2 for (ii))
two strands with specific base pairing;
large number of hydrogen bonds (between strands);
helix/coiling reduces chance of molecular damage / protects H bonds;
strong sugar-phosphate backbone;
(reject strong bonds between nucleotides)2 max [6] Total 25
Unit 2- Woodford County High School