Topic 8 Exam questions

Question 1

What is a substitution mutation?
(1)

Answer 1

1. Replacement of a base by a different base (in DNA);

Question 2

Describe how alterations to tumour suppressor genes can lead to the
development of tumours. (3)

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;

Question 3

Define what is meant by epigenetics. (2)

Answer 3

) 1. Heritable changes in gene function;
2. Without changes to the base sequence of DNA;

Question 4

In eukaryotes, transcription of target genes can be stimulated or inhibited
when specific transcriptional factors move from the cytoplasm into the
nucleus.
Oestrogen, methyl groups and acetyl groups are control factors that can
play a role in initiating transcription.
Explain how increased methylation could lead to cancer. (3)

Answer 4

) 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 5

Give one way in which benign tumours differ from malignant tumours. (1)

Answer 5

Cells of benign tumours cannot spread to other parts of the body /
metastasise;
OR
Cells of benign tumours cannot invade neighbouring tissues

Question 6

Explain how the methylation of tumour suppressor genes can lead to
cancer. (3)

Answer 6

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

Question 7

What is meant by a genome? (1)

Answer 7

(All) the DNA in a cell/organism;

Question 8

Describe and explain how the polymerase chain reaction (PCR) is used to
amplify a DNA fragment. (4)

Answer 8

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.