Biology for CAPE Original material © Cambridge University Press 2011 1

8 Answers to end-of-chapter questions 1 B [1]

2 A [1]

3 B [1]

4 B [1]

5 B [1]

6 A [1]

7 C [1]

8 A [1]

9 A [1]

Structured questions

10 a • Cutting the gene / length of DNA for insulin from genome

• From mRNA carrying information for making insulin • From the amino acid sequence for insulin Any 2 points [2]

b i Restriction / restriction endonucleases [1] ii BamH1 [1] iii

iv • Sticky ends produced / the terminal portion has a stretch of

unpaired nucleotides [1] • the strands are not of the same length [1]

v • DNA ligase [1]

• Is used to link together the deoxyribose–phosphate backbones of the DNA molecule producing a closed circle of the double-stranded DNA [1]

tetracycline-resistance gene

sticky ends

Good drawing showing correct cut [1] Labels [1]

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vi • Adding of calcium ions to make the membrane more permeable / by heat shock / adding calcium ions at 0 °C and raising it to 40 °C suddenly

• Or by electrophoresis Any point [2] vii Cloning of the treated bacteria [1] c • Screening of the bacteria to determine which have the

recombinant DNA • Multiplication / cloning of selected colony with insulin gene • Expression of gene / production of insulin Any 2 points [2]

11 a • Adding a gene that causes fluorescence under ultraviolet light

• Adding a gene that produces a harmless product that can be stained Any point [1]

b i

plasmid rejoined, insulin gene joins insulin gene tetracycline-resistance with itself to form added to For each

gene rejoined a closed circle plasmid, outcome drawing [1] forms closed Labels / circle explanations [1] [max 6] ii Antibiotic resistance [1]

iii Exposed to ampicillin • The 3 black and 3 grey colonies survive exposure to

ampicillin • The bacteria would have taken up the plasmid with the

ampicillin-resistance gene • These bacteria will include recombinant and non-recombinant

plasmids • The circular foreign DNA which were taken up by some

bacteria (white colonies) did not have the ampicillin- resistance gene and did not survive 1 point 1 mark [max 3] Exposed to tetracycline • Any colonies that are resistant to tetracycline would not have

the foreign DNA • These colonies would survive / the grey colonies • If the foreign DNA is added to the plasmid, the tetracycline

gene would be disrupted • These colonies would die / the black colonies 1 point 1 mark [max 4]

Biology for CAPE Original material © Cambridge University Press 2011 3

Essay questions 12 a • Made in bacteria

• Used to cut up viral DNA • To protect the bacteria from invading viruses / phages 5 points [3] • Cut specific base sequences 3–4 points [2] • Used in genetic engineering 1–2 points [1]

b • Obtain the required gene (cDNA) using mRNA carrying information for

making insulin and reverse transcriptase • Make the single-stranded cDNA double stranded and with sticky

ends • Use restriction enzyme to cut the vector plasmid / pBR322 • Vector has 2 antibiotic-resistance markers • The tetracycline-resistance gene would be cut by restriction enzyme • Mix the cut vector plasmid with the insulin DNA fragments and

DNA ligase • Mix the plasmids / vector with the host cells / bacterial cells • Incubate in a calcium chloride solution to make bacterial cells more

permeable to the plasmids • Allow the bacteria to clone themselves • Screen the colonies to determine which ones have the insulin gene • Using replica plating, subject the colonies to ampicillin 14–15 points [7] • The colonies that die do not have a vector / plasmid / antibiotic- 12–13 points [6]

resistance markers 10–11 points [5] • Subject the rest of the colonies to tetracycline 8–9 points [4] • The colonies that die contain the insulin gene since tetracycline gene 6–7 points [3]

is inactivated 4–5 points [2] • These colonies are cloned and the insulin gene expressed 2–3 points [1]

c • Advantage: simple procedure

• Disadvantage: could increase the risk of other, potentially pathogenic, bacteria taking up the genes and becoming resistant to antibiotics [2]

d • Cheaper

• More efficient than collecting from animals • Identical to human insulin so better response / little immune reaction Any point [1] • Ethical / religious reasons for not collecting from animals [max 3]

13 a • DNA made by joining lengths of DNA from two different species [1]

• Organism which possesses DNA / genes from another species and which is incorporated in their genome and actually expressed. They are created to produce a new phenotype [1]

b Benefits • The social impact has to do with its potential and actual impact on

human society and individuals • Higher crop yields so that people have more food • Enhance the nutritional content of crops (e.g. Golden Rice™) so

that people are better fed / fewer deficiency diseases • Permit better targeted clean-up of wastes and pollutants

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• Lead to production of more effective and cheaper medicines and treatments (e.g. insulin)

Potential hazards • Produce super-weeds or otherwise interfere with ecosystems in

unexpected ways, reducing crop yields so that people have less food

• Increase costs of seed • Some seeds cannot be used for sowing the next year since they

are modified to prevent germination thereby reducing crop production / increasing debt burdens

• Cause antibiotics to become less useful Any well-discussed point [1] • Any valid point [max 6]

c • Ethical impact is to do with issues of whether it is right or wrong, good

or bad to conduct research and develop genetically modified organisms (GMOs) [1]

• It is good to conduct such research to develop GMOs that might improve nutrition, the environment and health

• It is wrong to continue such research when the potential impact of the technology is unknown and many aspects of it remain to be understood

• It is wrong to use the results of such research when it involves release of GMOs into the environment as once it is released it cannot be taken back / there are unknown risks

• Any valid point Any 4 well described points [4] 14 a • The treatment of a disease by manipulating the genes in a person’s

cells • Treatment of a genetic disorder by altering a patient’s genotype /

genome Any point [2] b • Dominant allele can mask defective recessive allele when added to

the genome • Recessive allele does not have to be removed / inactivated / switched

off • Dominant disease allele would have to be inactivated which is very

difficult to do Any 2 points [2] c • Person suffering from CF has faulty CFTR protein

• Chloride ion channels are defective • Results in thick mucus in respiratory passages • Faulty CFTR alleles are recessive single gene disorder • Somatic gene therapy employed • Normal allele is inserted into liposomes / vector • The vector / liposomes are introduced into patient by nasal sprays • The liposomes move through the plasma membrane carrying the

dominant allele • The allele must be incorporated into the affected cells / host’s

DNA 12–13 points [6] • The dominant normal allele should be transcribed and then 10–11 points [5]

translated 8–9 points [4] • A normal protein would be produced 6–7 points [3] • Symptoms should be relieved 4–5 points [2] • Since it is somatic / cells die, treatment has to be repeated 2–3 points [1]

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d Benefits

• Cures the patient / no longer suffers from the disease • Relieves some symptoms • Can now lead a normal life Any 2 benefits [2] Hazards • Allele may be inserted into another gene, altering the product /

disrupting its function • Allele may be inserted into tissue other than target tissue with

unknown consequences • Allele may be inserted into germ line and passed via gametes • Virus which carries allele may damage the tissue • Allele may be inserted into a promoter of a gene and may

interfere with gene switching • Allele may be inserted in a position where it affects the genes that

normally control the cell cycle • Any valid point Any 3 hazards [3]