Question 1
1
Tobacco smoke contains a number of mutagens that are known to induce lung tumours in rodents, including NNK, a nitrosamine. The graph shows the relationship between NNK and lung tumour incidence in male rats. NNK was administered by subcutaneous injection for 20 weeks. Data points on the graph show percentage incidence of lung cancer in treatment groups of between 20 and 80 rats. Graph removed for copyright reasons
14 marks
Question 1(b)
1(b)
Explain the effects of mutagens such as NNK.
Mediumstructured2 marks
Answer
a. NNK/mutagens alter «base» sequence of DNA/alter genes/create new alleles b. increases rate/frequency/incidence of mutations c. in oncogenes/in genes that control cell division/mitosis d. tumors/cancers «develop/grow» if cell division/mitosis is uncontrolled 2 max 1. b \(42 \mathrm{nmol} \mathrm{ml}^{-1}\)
Question 1(e)
1(e)
Rates of lung cancer in smokers are high. Discuss whether it can be concluded from the evidence in the two graphs that NNK causes lung cancer in smokers. Nicotine addiction is the reason that people continue to smoke. Nicotine replacement therapy (NRT) is often used to help people quit smoking. Concerns about the safety of NRT led to a study where mice were given nicotine in drinking water and NNK was administered by subcutaneous injection. The table shows the effect of nicotine consumption on NNK-induced lung tumours in the mice. Table removed for copyright reasons
Hardessay3 marks
Answer
Answers supporting the conclusion a. first graph/data/research shows that NNK induces lung tumors/causes cancer b. second graph shows that smokers have absorbed NNK «from smoke»/shows that there is NNK in the blood of smokers Answers giving reservations about the conclusion c. results are for rats not humans d. injection of NNK and not inhalation of tobacco smoke e. dosage of NNK much larger than amounts likely in smokers f. other chemicals in smoke could cause lung cancer «in addition to those caused by NNK»/no proof that NNK is the only cause 3 max
Question 1(f)
1(f)
Describe the results when the mice were injected with NNK.
Mediumstructured2 marks
Answer
a. all/ 100 % «of mice/in treatment group 3/in treatment groups 3 to 6 » had tumours b. tumours per «significantly» increased «by NNK» c. no/little difference when nicotine was added «to mice with NNK» 2 max
Question 1(g)
1(g)
Evaluate the hypothesis that nicotine is not a mutagen.
Hardstructured3 marks
Answer
hypothesis supported (relevant treatment groups indicated with T numbers) a. «by itself» nicotine did not increase percentage «of mice» with tumours «T1 versus T2» OR percentage with tumours went down from 31 to 26 with nicotine «T1 versus T2» OR second treatment group does not have a higher percentage than first group b. «by itself» nicotine did not increase the number of tumours per mouse «T1 + T2» OR second treatment group does not have more tumours per mouse than first group c. in mice given NNK nicotine did not increase tumours «significantly» «T3 versus T4/5/6» OR 100\% of rats already had tumours with NNK only «T3» OR no significant difference/more tumours per mouse in \(5^{\text {th }}\) treatment group than \(4^{\text {th }} / 6^{\text {th }}\) even though nicotine was given for a shorter time/for only 2 weeks «T5 versus T4/6» d. if nicotine was mutagenic there would have been more tumours hypothesis not supported e. mice and humans may react to/metabolize nicotine differently/OWTTE f. nicotine from tobacco smoke may have different effects «from ingested nicotine» 3 max
Question 6
6
The genetic code is shown. In a coding gene, the DNA triplet in the transcribed strand is changed from AGG to TCG. What would be the result of this change in the genome? A. A non-functional protein B. A different but functional protein C. No change in the protein D. Termination of the polypeptide
Hardmcq1 marks
Answer
C
Question 7
7
A mutation in which type of cell could be inherited? Beta cell in the pancreas T-cell in the lymph Sperm cell in the testis Skeletal muscle cell in the diaphragm
Easymcq1 marks
Answer
C
Question 8
8
What is a feature of mutations? They occur randomly. They only occur in germ cells. The frequency cannot be increased by external factors. They only occur in certain base sequences of the genome.
Easymcq1 marks
Answer
A
Question 2
2
Psammonobiotus balticus belongs to a group of protists (unicellular eukaryotic organisms) that have a shell surrounding most of the cell, which provides shelter from predators. The graph shows the frequency of varying shell lengths in a population of P. balticus.
structured5 marks
Question 2(c)
2(c)
Mutations may increase variation within a species. Compare and contrast substitution and insertion mutations.
Mediumstructured2 marks
Answer
Similarity: a. both involve changes in the sequence of DNA/bases/nucleotides/triplets OR both may cause the production of a different amino acid/protein/polypeptide; Difference: b. substitution changes a base/nucleotide while insertion adds a base/nucleotide OR substitution changes one triplet while insertion changes more / causes frameshift OR substitution may not change protein/polypeptide function while insertion usually does; Accept codon in place of triplet. b. the contrast between substitution and insertion must be clear. 2 max
Question 8
8
The effect of substitution mutations in a salamander gene was studied. Some mutations have no observable effect on the phenotype and are called silent mutations. What conclusion about the position of the mutation in the codon can be drawn from this graph?
Mediummcq1 marks
Answer
D
Question 11
11
What is gene knockout used for? Increasing protein production by editing a gene Investigating the function of a gene by replacing it to make it inoperative Identifying the presence of a gene by editing it to produce a different protein Editing a gene to initiate cell death
Easymcq1 marks
Answer
B
Question 11
11
What change causes sickle cell anemia? A. One amino acid less in a polypeptide of hemoglobin B. A mutation leading to an extra codon in the genome C. Thymine replacing adenine in DNA D. Failure of tRNA to correctly transcribe the sequence of codons from mRNA
Mediummcq1 marks
Answer
C
Question 11
11
A base substitution in a gene has changed a codon. Which of these consequences could result from a base substitution in a codon? I. Another amino acid will be incorporated in the protein II. A stop codon is generated III. The same protein will be synthesized A. I only B. I and II only C. I and III only D. I, II and III
Mediummcq1 marks
Answer
D
Question 11
11
Knockout organisms are used as models in research. The p53 knockout mouse is named after p53, a gene which codes for a protein that normally suppresses the growth of cancerous tumours. How could scientists use p53 knockout mice in cancer research? To extract tumour suppressor protein from p53 knockout mice for cancer treatments To obtain functional copies of the p53 gene to use in gene replacement therapy To investigate the effect of new anti-cancer drugs on mouse tumours To study the effect of mutations on the expression of the p53 gene
Mediummcq1 marks
Answer
C