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Date	May 2017	Marks available	4	Reference code	17M.2.SL.TZ1.5
Level	Standard level	Paper	Paper 2	Time zone	Time zone 1
Command term	Describe	Question number	5	Adapted from	N/A

Question

DNA research, involving biotechnology, has led to benefits for society but has given rise to some controversy.

Outline how translation depends on complementary base pairing.

[3]

Describe the polymerase chain reaction (PCR), including the role of Taq DNA polymerase.

[4]

Explain benefits and risks of using genetically modified crops for the environment and also for human health.

[8]

Markscheme

a. translation converts a sequence of mRNA nucleotides/codons to a sequence of amino acids/polypeptide/protein

b. «triplets of» nucleotides/bases on «activated» tRNAs pair with complementary «triplets of» nucleotides/bases on mRNA / vice versa

c. base pairing occurs when adenine/A pairs with uracil/U and guanine/G pairs with cytosine/C

d. specific amino acids are attached to specific of tRNA

e. mRNA has codons AND tRNA has anticodons

a. PCR is process by which a small sample of DNA can be amplified/copied many times

b. PCR involves repeated cycling through high and lower temperatures «to promote melting and annealing of DNA strands»

c. «mixture» is heated to high temperatures to break «hydrogen» bonds between strands of DNA/to separate the double-stranded DNA

d. Taq DNA polymerase can withstand high temperatures without denaturing

e. primers bind to «targeted» DNA sequences at lower temp

f. Taq DNA polymerase forms new «double-stranded» DNA by adding «complementary» bases/nucleotides

Environment benefits:

a. pest-resistant crops can be made

b. so less spraying of insecticides/pesticides

c. less fuel burned in management of crops

d. longer shelf-life for fruits and vegetables so less spoilage

e. greater quantity/shorter growing time/less land needed

f. increase variety of growing locations / can grow in threatened conditions

Environment risks:

g. non-target organisms can be affected

h. genes transferred to crop plants to make them herbicide resistant could spread to wild plants making super-weeds

i. GMOs (encourage monoculture which) reduces biodiversity

j. GM crops encourage overuse of herbicides

Health benefits:

k. nutritional value of food improved by increasing nutrient content

l. crops could be produced that lack toxins or allergens

m. crops could be produced to contain edible vaccines to provide natural disease resistance

Health risks:

n. proteins from transferred genes could be toxic or cause allergic reactions

o. antibiotic resistance genes used as markers during gene transfer could spread to «pathogenic» bacteria

p. transferred genes could cause unexpected/not anticipated problems
OR
health effects of exposure to GMO unclear

Examiners report

[N/A]

Syllabus sections

Core » Topic 2: Molecular biology » 2.7 DNA replication, transcription and translation

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