3.8.2 Gene Expression is controlled by a number of features.

Question 1

How do alterations to tumour
suppressor genes lead to
cancer. (4)

Answer 1

1. Increased methylation (of tumour suppressor genes);
2. Mutation (in tumour suppressor genes);
3. Tumour suppressor genes are not transcribed/expressed/mRNA not produced OR Amino acid sequenceor
   different amino acid/primary or tertiary structure altered;
4. (Results in) rapid/uncontrollable cell division/cell division not regulated;

Question 2

What is a Transcription Factor? (3)

Answer 2

1. (Protein/molecule) that moves from cytoplasm to DNA;
2. (TF) binds to specific gene/genes/ to specific part of/site on DNA/ binds to promoter/RNA polymerase;
3. Leads to/blocks (pre)mRNA production / allows/blocks binding of RNA polymerase

Question 3

How does oestrogen stimulate
Transcription? (6)

Answer 3

1. Oestrogen diffuses through the cell membrane;
2. attaches to receptor;
3. receptor changes shape;
4. receptor leaves protein complex which inhibited its action;
5. oestrogen receptor binds to promoter region;
6. enables RNA polymerase to transcribe target gene

Question 4

Describe RNA Interference. (3)

Answer 4

1. MicroRNA/siRNA binds to cell’s mRNA by specific base pairing;
2. (So) prevents mRNA being read by ribosomes;
3. prevents translation/production of proteins

Question 5

Define Epigenetics. (2)

Answer 5

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

Question 6

Describe how methylation
leads to cancer. (3)

Answer 6

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/mitosis;