Paper 3 2021

Question 1

Answer 1

• pre-)mRNA splicing / post-transcriptional modification (1)
  • different exons removed (1)
  • (therefore) producing different {sequences of amino acids
  / mRNA sequences} (1)

Question 2

Answer 2

• {hormones / signal molecules / chemical signals} bind to
receptors found only in some {tissues / cells} (1)
• regulating a {transcription factor / repressor molecules}
(1)
• {transcription factor / repressor molecule} binds to the
promotor region of the (acetylcholinesterase) gene (1)
• therefore switching {on / off} transcription (1)

EXTRA: promoter region is a a sequence

Question 3

Answer 3

• concentration between 25 and 50 μmol dm-3 (1)
• concentration having greatest inhibitory effect (1)
• but having no effect on cell viability (1)

Question 4

Answer 4

• adrenaline carried in the blood (1)
• (acts on the) sinoatrial node (1)
• increasing the frequency of impulses {produced by the
SAN / that spread across the heart} (1)
• increasing the rate at which the heart contracts

Question 5

Answer 5

• the ratio of the rate of an enzyme reaction taking place at temperatures differing by 10 (℃ or K).

• description of how two suitable temperatures will be
controlled e.g. using 2 water baths with a 10 degrees difference (1)
• provide excess triglyceride (1)?
• control concentration of lipoprotein lipase (1)
• measure concentration of {triglyceride / fatty acids } at stated time intervals (1)
• find initial rates (1)
• description of how Q10 can be determined e.g. Rate at T + 10 divided by the rate at T(1)

Extra: triglyceride(fat) made from 1 glycerol and 3 fatty acids. The enzyme LPL breaks down triglycerides.

Question 6

Answer 6

• Mitosis for growth and repair
• (Zygote to fetus) proliferation and differentiation
• Meiosis for genetic variation
• Production of gametes
• Inheritance of alleles predisposing to genetic disease / some cancer
• Mutations result in loss of control of cell division in cancers
• Clonal amplification in immune system
• Binary fission of bacterial cells
• Some antibiotics work by inhibiting bacterial cell division

Question 7

Answer 7

• extract mRNA for one form of the (tau protein) (1)
• copy mRNA into DNA (1)
• use restriction enzymes {to create sticky ends) / cut the
DNA and a vector} (1)
• {ligate / insert / integrate} the TAU DNA into the vector
(DNA) (1)
• introduce vector into {fertilised egg / embryonic stem /
zygote / cells / neural cell stem cells} (1)