Genetic, Evolution, & Ecosystems OCR 47 Review Summary Questions 2024

19.1 Discuss why beneficial mutations are rare & suggest a process that beneficial mutations underpin (4 MARKS) - ️️Majority of mutations are silent (1); idea that random change to protein structure is more likely to reduce function (1); idea that beneficial mutations increase chances of survival if environment changes (1); surviving organisms reproduce and pass new alleles to offspring (1); leading to evolution (1) 19.1 Outline why majority of mutations do not have an influence phenotype (2 MARKS) - ️️Mutation is random (1); majority of DNA is non-coding; mutations more likely to occur in non-coding regions (1); mutations in non-coding regions do not affect phenotype (1) 19.1 The development of lactose tolerance is thought to have spread over approx. 20,000 years, which is very quick in evolutionary terms. Explain why % of adults with ability to digest lactose increased at such a rate (2 MARKS) - ️️Ability to digest lactose is a beneficial characteristic (1); drinking milk prevented starvation (1); reduced osteoporosis (1); directional selection (1) 19.2 Another e.g. of gene regulation in prokaryotes is trp operon, which codes for production of tryptophan, and essential amino acid for bacterium E. coli. When tryptophan is available in environment, the structural genes in trp operon aren't expressed. Suggest mechanism for genetic regulation of this operon (5 MARKS) - ️️Tryptophan binds to repressor protein (1); shape of repressor protein changes (1); repressor protein binds to promoter (1); blocks RNA polymerase from binding (1); transcription prevented (1); of genes coding for enzymes responsible for tryptophan synthesis (1) 19.2 Lac operon if referred to as being 'leaky' meaning it's still transcribed to limited extent even in lactose absence. a) Using your knowledge of how lac operon works, explain why this is necessary (3 MARKS) b) Suggest functions of β-galactosidase & lactose permease synthesised by lac operon (3 MARKS) - ️️a) enzyme coded for by lac operon enables lactose to enter bacteria (1); lactose binds to repressor protein; (repressor) protein changes shape (1); transcription no longer blocked (1); enzymes needed to metabolise lactose are synthesised (1) b) β-galactosidase catalyses the hydrolysis of lactose (1); to galactose and lactose (1); lactose permeate enables the entry of lactose into cells (1) 19.2 Using your knowledge of enzymes, explain how enzyme cofactors could play a role in gene regulation (4 MARKS) - ️️Cofactors bind to proteins that regulate transcription (1); changes