Topic 8 Exam Questions: The Control Of Gene Expression

Question 1

8.1 - Gene Mutations

Explain how a single base substitution causes a change in the structure of this polypeptide (not transcription or translation) (3)

Answer 1

1. Change in (sequence of) amino acids/primary structure
2. Change in hydrogen/ionic/disulfide bonds
3. Alters tertiary structure

Question 2

8.1 - Gene Mutations

What is a substitution mutation? (1)

Answer 2

Replacement of a base by a different base (in DNA)

Question 3

8.2 - Cancer

Throat cancer is caused by increased methylation of promoter region of tumour suppressor gene. Methylation is caused by enzyme DNMT. EGCG is a competitive inhibitor of DNMT and allows daughter cells to produce mRNA from tumour suppressor gene. Suggest how EGCG allows the production of mRNA in daughter cells. (3)

Answer 3

1. (EGCG) bind to active site of DNMT
2. (DNMT) can’t methylate (promotor region of tumour suppressor gene)
3. Transcriptional factor can bind (to promotor region)
4. RNA polymerase (stimulated/activated)

Question 4

8.2 - Cancer

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

Answer 4

1. (Increased) methylation (of tumour suppressor genes)
2. Mutation (in tumour suppressor genes)
3. Tumour suppressor genes are not transcribed/expressed OR amino acids sequence/primary structure altered
4. (Results in) rapid/uncontrolled cell division

Question 5

8.2 - Cancer

ATM binds to stop cell division until DNA is repaired. A mutation could result in a person having non-functional forms of gene that produces ATM. What can you predict about the possible effects of having non-functional form if ATM? (3)

Answer 5

1. ATM will not bind to DNA
2. DNA not repaired
3. Cell division continues/tumour forms
4. Tumour suppressor (gene) not effective/activated
5. May have no effect in diploid/heterozygous (organism)
6. (Which) still has a functional ATM/ATM gene

Question 6

8.2 - Cancer

Define what is meant by epigenetics. (2)

Answer 6

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

Question 7

8.2 - Cancer

Explain how increased methylation could lead to cancer. (3)

Answer 7

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 8

8.2 - Cancer

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

Answer 8

Cells of benign tumour can’t spread to other parts of the body/metastasise OR
cells of benign tumours can’t invade neighbouring tissues

Question 9

8.2 - Cancer

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

Answer 9

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

Question 10

8.2 - Cancer

MM is caused by a faulty receptor protein in cell-surface membranes. Cells in MM tumours can be destroyed by the immune system. Suggest why they can be destroyed by the immune system. (3)

Answer 10

1. Faulty protein recognised as an antigen
2. T cells will bind to faulty protein/to (this) ‘foreign’ protein
3. (Sensitised) T cells will stimulate clonal selection of B cells
4. (Resulting in) release of antibodies against faulty protein.

Question 11

8.2 Epigenetics and RNA interference

One method of transferring RNAi molecules into cells involves combining these molecules with a lipid. Suggest why this increases uptake of RNAi molecules into cells (1)

Answer 11

(Cell/memebrane has a) phospholipid bilayer
OR
no channel/carrier protein (for uptake)
OR
No need for channel/carrier protein (for uptake)

Question 12

8.2 Epigenetics and RNA interference

Testosterone is asteroid hormone. Steroid hormones are hydrophobic. Explain why steroid hormones can rapidly enter a cell by passing through its cell-surface membrane. (2)

Answer 12

1. Lipid soluble
2. (Diffuse through) phospholipid (bilayer)

Question 13

8.2 Epigenetics and RNA interference

Suggest and explain why testosterone binds to specific AR (androgen receptor). (2)

Answer 13

1. Has a (specific) tertiary structure/shape
2. (Structure are) complementary

Question 14

8.2 Epigenetics and RNA interference

The binding of testosterone to a specific receptor changes the shape of the receptor. The receptor now enters the nucleus and stimulates gene expression. Suggest how the receptor stimulates gene expression. (2)

Answer 14

1. (Receptor is) a transcription factor
2. Binds to DNA/ promoter
3. (Stimulates) RNA polymerase

Question 15

8.2 Epigenetics and RNA interference

Suggest and explain one way epigenetics may affect the age when symptoms of Huntington’s disease start. (2)

Answer 15

1. (Increased) methylation of DNA/gene/allele
2. Inhibits/prevents transcription
   OR 3. Decreased methylation of DNA/gene/allele
3. Stimulates/allows transcription
   OR 5. Decreased acetylation of histones
4. Inhibits transcription
   OR 7. Increased acetylation of histones
5. Stimulates /allows transcription

Question 16

8.2 Epigenetics and RNA interference

Scientists began by lysing cells and organelles using detergent that dissolves lipids in water to investigate the role of a protein called CENP-W in mitosis. Suggest how the detergent releases CENP-W from cells. (2)

Answer 16

1. Cell membranes made from phospholipid
2. (Detergent) dissolves membranes/phospholipid (bilayer)

Question 17

8.2 Epigenetics and RNA interference

Explain how ultracentrifugatuon separated protein CENP-W from other molecules. (2)

Answer 17

1. Spin (liquid/supernatant) at (very) high speed
2. Molecules/ CENP-W separates depending on (molecular) mass/size/density

Question 18

8.2 Epigenetics and RNA interference

Explain how increased methylation could lead to cancer. (3)

Answer 18

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 19

8.2 - Stem cells

Suggest how the growth of new blood vessels into damaged heart tissues could increase the rate of repair of tissues. (3)

Answer 19

1. Greater blood supply (to damaged areas)
2. Bringing more oxygen / glucose for respiration
3. Brings more amino acids for protein synthesis
4. For cell repair/mitosis/division

Question 20

8.3 - Genome Projects

Suggest and explain how the viruses became able to infect other species of frog. (2)

Answer 20

1. Mutation in viral DNA/RNA/genome/genetic material
2. Altered (tertiary structure of the) viral attachment protein
3. Allows it/attachment protein/virus to bind (to receptors of other species

Question 21

8.3 - Genome Projects

Name two techniques the scientists may have used when analysing viral DNA to determine the viruses were closely related (1)

Answer 21

1. The polymerase chain reaction
   2 . Genetic/DNA fingerprinting
   3 (Gel) electrophoresis
2. DNA/genome sequencing

Question 22

8.3 - Genome Projects

Determining the genome of a virus could allow scientists to develop a vaccine. Explain how. (2)

Answer 22

1. Scientists could identify proteins (that derive from the genetic code)
   OR could identify the proteome
2. Could then identify potential antigens (to use in the vaccine)

Question 23

8.3 - Genome Projects

Describe how the B lymphocytes would respond to vaccination against Ranavirus. (3)

Answer 23

1. B cell (antibody) binds to (viral) specific/complementary receptor/antigen
2. B cell clones OR B cell divides by mitosis
3. Plasma cells release/produce (monoclonal) antibodies (against the virus)
4. (B/plasma cells produce/develop) memory cells

Question 24

8.3 - Genome Projects

What is meant by a genome? (1)

Answer 24

(All) the DNA in a cell/organism

Question 25

8.3 - Genome Projects Explain why the antibody binds to the transcription factor. (2)

Answer 25

1. (Transcriptional factor/antibody) has a specific tertiary structure/shape 2. Complementary (shape/structure)

Question 26

8.4 - DNA probe and Gel Electrophoresis The scientists used a radioactively labelled DNA probe to show that the cells of tobacco leaves contained the SUT1 (sucrose co-transport protein). Describe how they would do this. (4)

Answer 26

1. Extract DNA and add restriction enzymes 2. Separate fragments using electrophoresis 3. (Treat DNA to) form single strands OR (treat DNA to) expose bases 4. The probe will bind to/hybridise/base pair with the SUT1/ gene 5. Is autoradiography/ X ray film (to show the bound probe)

Question 27

8.4 - DNA probe and Gel Electrophoresis What is a DNA probe? (2)

Answer 27

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

Question 28

8.4 - DNA probe and Gel Electrophoresis Describe how the DNA is broken down into smaller fragments (2)

Answer 28

1. Restriction enzyme 2. (Cuts DNA at specific) base sequence OR (breaks) phosphodiester bonds OR (cuts DNA) at recognition /restriction site

Question 29

8.4 - DNA probe and Gel Electrophoresis Explain why the DNA is treated to make it single stranded. (1)

Answer 29

(So DNA) probe binds/attaches/anneals

Question 30

8.4 - DNA probe and Gel Electrophoresis What is meant by a non-coding base sequence? (1)

Answer 30

Doesn’t code for amino acid/tRNA/rRNA

Question 31

8.4 - DNA probe and Gel Electrophoresis Name the process by which a base in base sequence is lost (1)

Answer 31

Deletion mutation

Question 32

8.4 - DNA probe and Gel Electrophoresis Give the name of the method they used to clone the DNA in vitro (1)

Answer 32

(The) polymerase chain reaction

Question 33

8.4 - DNA probe and Gel Electrophoresis Explain how DNA probes are used to produce results (3)

Answer 33

1. Probes are single stranded /have a specific base sequence 2. Complementary base sequence on (specific) spacer *spacer is non-coding base sequences OR 3. Complementary/specific to (particular) spacer 4. Binds (to single stranded spacer) and glows /produces light/fluoresce

Question 34

8.4 - DNA probe and Gel Electrophoresis Suggest and explain why it is important to be able to identify the specific strain of M.tuberculosis infect a patient. (2)

Answer 34

1. To see if strain is resistant to any antibiotics 2. Soo can prescribe effective /right antibiotic OR 3. See whether (any) vaccine works against this strain/see which vaccine to use/to produce specific vaccine 4. (So) can vaccinate potential contacts/to stop spread OR 5. Can test other people to see if they have the same strain/trace where people caught TB 6. Allowing control of spread of disease/vaccinate/treat contacts (of people with same strain) before they get TB

Question 35

8.4 - Recombinant DNA describe how enzymes could be used to insert a gene into a plasmid (2)

Answer 35

1. Restriction enzymes cuts plasmid OR restriction enzyme produces ‘sticky ends’ 2. Ligase joins gene/DNA and plasmid OR ligase joins ‘sticky ends’

Question 36

8.4 - Recombinant DNA Suggest and explain how a delayed insertion of a gene could produce offspring of a fish without the desired characteristic(2)

Answer 36

1. Cell division has occurred (before gene added) 2. (Cells producing ) gametes don’t receive the gene

Question 37

8.4 - Recombinant DNA Describe the roles of two named types of enzymes used to insert DNA fragments into plasmids. (2)

Answer 37

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

Question 38

8.4 - Recombinant DNA Explain the role of reverse transcriptase (1)

Answer 38

Produces (c)DNA using (m)RNA

Question 39

8.4 - Recombinant DNA Explain the role of DNA polymerase (1)

Answer 39

Joins NUCLEOTIDES to produce (complementary strands/of) DNA

Question 40

8.4 - Recombinant DNA Any DNA in the sample is hydrolysed by enzymes before the sample is added to the reaction mixture. Explain why. (2)

Answer 40

1. To remove any DNA present 2. As this DNA would be amplified/ replicated

Question 41

8.4 - Recombinant DNA Suggest one reason why DNA replication stops in the polymerase chain reaction. (1)

Answer 41

Limited number of primers/nucleotides

Question 42

8.4 - Recombinant DNA The scientists used a variety of primers to detect the presence of different RNA in viruses. Explain why. (2)

Answer 42

1. Base sequences differ 2. (Different) COMPLEMENTARY primers required

Question 43

8.4 - Recombinant DNA Describe how a geneticist would attempt to insert copies of a gene into plasmids (3)

Answer 43

1. Cut plasmid with a restriction endonuclease 2. (So that) both have complementary /sticky ends 3. (Mix together) and add ligase to join the complementary/sticky ends

Question 44

8.4 - Recombinant DNA Suggest why the scientists used a marker gene and why they used the gene. (2)

Answer 44

1. Not all cells would have taken up the plasmid successfully 2. Cells that took up the gene will glow

Question 45

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

Answer 45

1. (Requires DNA fragment) DNA polymerase, (DNA) nucleotides and primers 2. Heat to 95°C to break hydrogen bonds (and separate strands) 3. Reduce temperature soo primers bind to DNA/strands 4. Increase temperature, DNA polymerase joins nucleotides (and repeat method)