Unit 8 Gene Expression

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;

Question 7

Describe the method of in-vivocloning with the use of an antibiotic resistant marker gene (8)

Answer 7

1. isolate wanted gene / DNA from another organism / mRNA from cell / organism;
2. using restriction endonuclease / restriction enzyme / reverse transcriptase to get DNA and
3. produce sticky ends;
4. use ligase to join wanted gene to plasmid;
5. include marker gene e.g. antibiotic resistance;
6. add plasmid to bacteria to grow (colonies)then (replica) plate onto medium where the marker gene is expressed;
7. not killed have antibiotic resistance gene and (probably) the wanted gene

Question 8

Describe the process of invitro cloning using PCR (9)

Answer 8

1. DNA heated to 90 to 95°C;
2. strands separate;
3. cooled / to temperature below 70°C
4. primers bind; (primers identify the DNA sequence to be amplified)
5. nucleotides attach;
6. by complementary base pairing;
7. temperature 70 - 75°C;
8. DNA polymerase joins nucleotides together;
9. cycle repeated;

Question 9

Describe the use of DNA probes in gene testing. (4)

Answer 9

1. probe will attach ( e.g. to allele);
2. attaches to one DNA strand;
3. as a result of complementary base pairing;
4. radioactivity detected on film / X-ray / by autoradiography;

Question 10

Outline the process of genetic fingerprinting (10)

Answer 10

1. DNA extracted from sample;
2. DNA cut into segments using restriction endonucleases;
3. Must leave VNTR / required core sequences intact;
4. DNA fragments separated using electrophoresis;
5. detail of process e.g. mixture put into wells on gel and electric current passed through;
6. immerse gel in alkaline solution / two strands of DNA separated;
7. Southern blotting / over with nylon / absorbent paper (to absorb DNA)
8. DNA fixed to nylon / membrane using UV light;
9. radioactive marker / probe added complementary to VNTR;
10. (areas with probe) identified using X-ray film