TOPIC 8 EXAM QUESTIONS

Question 1

Explain how a single base substitution causes a change in the structure of
this polypeptide.

Answer 1

1. Change in (sequence of) amino acid(s)/primary structure;
   Reject amino acids are formed.
   Reject amino acids code.
2. Change in hydrogen/ionic/disulfide bonds;
3. Alters tertiary/30 structure;

Question 2

Describe how alterations to tumour suppressor genes can lead to the
development of tumours

Answer 2

1. (Increased) methylation (of tumour suppressor genes);

Accept abnormal methylation or hypermethylation
Ignore decreased acetylation of histones
2. Mutation (in tumour suppressor genes);

3. Tumour suppressor genes are not transcribed/expressed

OR
Amino acid sequence/primary structure altered;
Accept mRNA for transcription/transcribed
Accept tertiary structure altered
Accept different amino acid
Ignore reference to protein not being formed

4. (Results in) rapid/uncontrollable cell division;
   Accept cell division cannot be regulated
   Ignore growth

Question 3

Explain how increased methylation could lead to cancer.

Answer 3

1. Methyl groups (could be) added to (both copies of) a tumour
   suppressor gene;
2. The transcription of tumour suppressor genes is inhibited;
3. Leading to uncontrolled cell division

Question 4

Explain how the methylation of tumour suppressor genes can lead to
cancer.

Answer 4

1. Methylation prevents transcription of gene;
2. Protein not produced that prevents cell division / causes cell
   death / apoptosis;
3. No control of mitosis.

Question 5

In the cytoplasm, testosterone binds to a specific androgen receptor (AR).
An AR is a protein.
Suggest and explain why testosterone binds to a specific AR

Answer 5

1. Has a (specific) tertiary structure/shape;
   Accept in context of AR or testosterone.
   Ignore 3D.
2. (Structures are) complementary;
   Reject reference to antigen

Question 6

The binding of testosterone to an AR changes the shape of the AR. This
AR molecule now enters the nucleus and stimulates gene expression.
Suggest how the AR could stimulate gene expression.

Answer 6

1. (AR is) a transcription factor;
   Ignore ‘binds to bases’ or ‘binds to gene’.
2. Binds to DNA/promoter;

Reject reference to active site, enzyme, substrate
or induced fit.

3. (Stimulates) RNA polymerase;

Question 7

Name two techniques the scientists may have used when analysing viral
DNA to determine that the viruses were closely related.

Answer 7

Name two techniques the scientists may have used when analysing viral
DNA to determine that the viruses were closely related.

Question 8

Name two techniques the scientists may have used when analysing viral
DNA to determine that the viruses were closely related.

Answer 8

Name two techniques the scientists may have used when analysing viral
DNA to determine that the viruses were closely related.

Question 8

Name two techniques the scientists may have used when analysing viral
DNA to determine that the viruses were closely related.

Answer 8

For one mark, accept any two of the following:
* The polymerase chain reaction
* Genetic/DNA fingerprinting
* (Gel) electrophoresis
* DNA/genome sequencing;

Question 9

Plants transport sucrose from leaves to other tissues for growth and storage.
SUT1 is a sucrose co-transporter protein.
Scientists investigated whether the cells of tobacco plant leaves used SUT1 to
transport sucrose to other tissues.
(a) The scientists used a radioactively labelled DNA probe to show that the
cells of tobacco plant leaves contained the SUT1 gene.
Describe how they would do this.
Do not include PCR in your answer.

Answer 9

1. Extract DNA and add restriction endonucleases/restriction enzymes;
2. Separate fragments using electrophoresis;
3. (Treat DNA to) form single strands
   OR
   (Treat DNA to) expose bases;
   Ignore method used to separate strands
4. The probe will bind to/hybridise/base pair with the SUT1/gene;
5. Use autoradiography (to show the bound probe);
   Accept use photographic or X ray film (to show the
   bound probe)
   X rays alone is not sufficient

Question 10

) What is a DNA probe?

Answer 10

1. (Short) single strand of DNA;
2. Bases complementary (with DNA/allele/gene);

Question 11

A scientist produced transgenic zebrafish.
She obtained a gene from silverside fish. The gene codes for a growth hormone
(GH).
She inserted copies of this GH gene into plasmids. She then microinjected these
recombinant plasmids into fertilised egg cells of zebrafish.
(a) Describe how enzymes could be used to insert the GH gene into a
plasmid.

Answer 11

1. Restriction endonucleases/enzymes cuts plasmid;
   OR
   Restriction endonucleases/enzymes produces ‘sticky ends’;
   Ignore restriction enzymes cuts out the gene.
   Reject restriction enzymes cuts the gene.
2. Ligase joins gene/DNA and plasmid
   OR
   Ligase joins ‘sticky ends’;

Question 12

) Describe the roles of two named types of enzymes used to insert DNA
fragments into plasmids.

Answer 12

1. Restriction (endonuclease/enzyme) to cut plasmid/vector;
2. Ligase joins gene/DNA to plasmid/vector;

Question 13

Explain the role of reverse transcriptase in RT-PCR

Answer 13

Produces (c)DNA using (m)RNA;

Question 14

Explain the role of DNA polymerase in RT-PCR

Answer 14

Joins nucleotides to produce (complementary strand/s of) DNA;

Question 15

Suggest one reason why DNA replication stops in the polymerase chain
reaction

Answer 15

Limited number of primers / nucleotides;

Question 16

Scientists have used the RT-PCR method to detect the presence of
different RNA viruses in patients suffering from respiratory diseases.
The scientists produced a variety of primers for this procedure.

Answer 16

1. Base sequences differ;
2. (Different) complementary primers required;

Question 17

Describe how the geneticist would attempt to insert copies of the HGH
gene into these plasmids.

Answer 17

1. Cut the plasmid with a restriction endonuclease;
   Allow ‘add base sequences to blunt ends of plasmid
   and HGH gene’
2. (So that) both have complementary / sticky ends;
3. (Mix together) and add ligase to join the complementary / sticky ends;

Question 18

Describe and explain how the polymerase chain reaction (PCR) is used to
amplify a DNA fragment.

Answer 18

1. (Requires DNA fragment) DNA polymerase, (DNA) nucleotides and
   primers;
2. Heat to 95 °C to break hydrogen bonds (and separate strands);
   Accept temperature in range 90 to 95 °C.
3. Reduce temperature so primers bind to DNA/strands;
   Accept temperature in range 40 to 65 °C.
4. Increase temperature, DNA polymerase joins nucleotides (and repeat
   method);
   Accept Taq polymerase for DNA polymerase.
   Accept temperature in range 70 to 75 °C.

Question 19

Recombinant DNA technology can involve the transfer of fragments of human DNA
into bacteria. The bacteria are then used to produce human proteins.
Give two reasons why bacteria are able to use human DNA to produce human
proteins.

Answer 19

1. (The) genetic/DNA code is universal
   OR
   The same triplets/codons code for the same
   amino acids (in all species);
2. (The mechanism of) transcription is
   universal;
3. (The mechanism of) translation is universal;

Question 20

Suggest and explain one reason why bacteria might not be able to produce every
human protein

Answer 20

Cannot splice (pre-mRNA), so cannot remove
introns
OR
Do not have Golgi (apparatus), so cannot
process/modify (proteins)
OR
Do not have transcriptional factors (required), so
cannot carry out transcription/produce mRNA;

Question 21

Explain the purpose of the marker gene.

Answer 21

Shows that the (antithrombin) gene has been
taken up (by cells/embryos/goats)
OR
Shows transgenic/transformed goat cells/goat
embryos/goats
OR
Allows detection of genetically modified cells/
organisms/mammals/goats;

Question 22

Mature leaves from slow-growing, shade-tolerant plants produce poisonous chemicals
that are a defence against being eaten by herbivores.
Suggest how this benefits slow-growing, shade-tolerant plants.

Answer 22

1. (In the shade, so) less/slower rate of
   photosynthesis;
2. (Slow-growing, so) would take a long time to
   replace (mature leaves)
   OR
   Leaves more likely to reach maturity
   OR
   Leaves take a long time to mature;
3. Plants can maintain (a large enough) surface
   area for photosynthesis
   OR
   Plants can absorb enough light