1.
The diagram shows a short section of a DNA molecule.
B
C
A
(a)
On the diagram draw a box round one nucleotide.
(1)
(b)
Use the letters in the diagram to indicate a part of the molecule which
(i)
is not a base and is different in an RNA molecule; .........................................
(ii)
contains nitrogen. .............................................................................................
(2)
(c)
(i)
The sequence of bases on one strand of DNA is important for protein synthesis.
What is its role?
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
How are the two strands of the DNA molecule held together?
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(1)
(iii)
Give one advantage of DNA molecules having two strands.
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(1)
(Total 6 marks)
The Queen Katherine School
1
2.
The diagram shows one nucleotide pair of a DNA molecule.
X
Y
(a)
Z
Q
Name the parts of the nucleotide labelled X, Y and Z.
X .....................................................
Y .....................................................
Z .....................................................
(3)
(b)
What type of bond holds Z and Q together?
.....................................................................................................................................
(1)
(c)
A sample of DNA was analysed. 28% of the nucleotides contained thymine. Calculate the
percentage of nucleotides which contained cytosine. Show your working.
Answer ....................................... %
(2)
(Total 6 marks)
The Queen Katherine School
2
3.
(a)
DNA and RNA are made of nucleotides. Give two ways in which the structure of a DNA
nucleotide differs from the structure of an RNA nucleotide.
DNA nucleotide
RNA nucleotide
(2)
(b)
The diagram shows one complete turn of a DNA helix. Within the complete turn of the
helix, each strand of DNA contains ten nucleotides.
Repeating sequence of
sugar-phosphate units
Specific
base pair
(i)
A particular human chromosome is 1m long and contains 125 000 000 complete
turns in its DNA helix. (1 mm is 106 nm). Use this information to calculate the
length of one nucleotide. Show your working.
Length ....................................... nm
(2)
(ii)
Describe how a protein is made from the information coded in DNA.
(Allow one lined page)
(7)
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3
(c)
Rapidly dividing cells were allowed to grow in a solution containing unlabelled thymine.
Some of these cells were transferred to a second solution in which all the thymine
molecules were radioactively labelled. Samples of cells were removed from the
radioactive solution after one division. Chromosomes from the cells were tested for
radioactivity. The results are shown in the table.
A
B
Chromosomes from cells
dividing in unlabelled
thymine.
No radioactivity
Chromosomes from cells
that divided once in
radioactive thymine.
All chromosomes radioactive
Use your knowledge of the semi-conservative mechanism of DNA replication to explain
why all the chromosomes in B were radioactive.
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(4)
(Total 15 marks)
4.
(a)
A nucleotide of DNA contains an organic base and two other components.
Name the two other components.
1 ..................................................................................................................................
2 ..................................................................................................................................
(2)
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4
(b)
A piece of DNA consisted of 17 base pairs. This piece was analysed to find how many
bases of each type were present in each of its two strands. Some of the results are shown
in the table.
Number of bases
A
Strand A
Strand B
6
T
G
C
2
5
Calculate the missing values for the number of bases and complete the table.
(2)
(c)
The cells in the heart and liver of a person are genetically identical but different in
appearance. Use your knowledge of genes to suggest why these cells are different in
appearance.
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.....................................................................................................................................
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(2)
(Total 6 marks)
The Queen Katherine School
5