Bio Short Answer Q

Several environmental factors can influence the rate at which ACR occurs. Describe how, and why, the rate of this reaction in mammalian cells would change as the temperature increases from 10C to beyond 70C. (4 marks)

• Initially, Temperature increases from 10C, and the Rate of reaction also increases

• As a result of temp increase, reactants and enzymes move around more, causing more collisions and thus catalysis

• At higher temp beyond cell optimal, ROR decreases rapidly

• Beyond 70C, enzymes have denatured, where active site shape is altered, and can no longer bind with substrates

What type of organisms is CRISPR-Cas9 sourced from? Briefly describe the role it plays in this organism. (3 marks)

• CRISPR-Cas9 is sourced from bacteria.

• In bacteria it acts as a defense mechanism against bacteriophages

(viruses that invade bacteria).

• It does this by storing a copy of some of the bacteriophages/viral DNA,

which it will then recognise and destroy if the cell is infected again in the

future.

Describe the steps involved in using CRISPR-Cas9 for gene editing. (4 marks)

• Synthetic guide RNA is created that has a complementary spacer to the target DNA that is to be cut.

• The guide RNA is mixed with a Cas-9 enzyme and a suitable complementary PAM sequence to create a CRISPR-Cas9 complex. This is injected into a cell.

• The Cas9 finds the target PAM sequence and cuts the selected sequence of DNA with a blunt cut.

• While the cell attempts to repair the cut DNA, selected nucleotides that scientists wish to introduce to the cell can be introduced.

Outline the consequences-based approach to bioethics and describe how it might be used to argue in favour of researching CRISPR-Cas9 utilising mice rather than humans. (3 marks)

• The consequences-based approach aims to maximise positive outcomes while minimising negative outcomes.

• Editing the genome of mice in experimental studies rather than humans means that any unexpected negative outcomes of such experiments are limited to animal subjects, rather than humans, which could be argued is aiming to minimise negative outcomes for humans.

• It could also be argued that the benefit that might be obtained from this research in terms of its applications to humans in areas such as disease and health, maximises positive outcomes.

Outline Inflammatory Response Process (3 marks)

• Mast cells detect the entry of a pathogen and release histamine.

• Histamine acts to recruit other immune cells to the site of infection and to make blood vessels more permeable, often causing redness and swelling.

• The invading pathogen is then destroyed through the actions of immune cells and complement proteins.

The DNA code can be described as both universal and degenerate. How do these terms apply to the synthesis of haemoglobin? (2 marks)

• The universal aspect of the DNA code means that the gene that encodes the haemoglobin protein will always encode the same protein, regardless of the organism.

• The degenerate nature of the DNA code refers to the fact that for most amino acids, multiple codons code for the same amino acid. This means that if there is a mutation during the transcription of the haemoglobin gene, it may not affect the final amino acid sequence.

Before a gene is sequenced for comparison, it is usually necessary to “amplify” the gene by making several copies of it. Name and describe the process used to achieve this. (4 marks)

• The process is polymerase chain reaction (PCR).

• The DNA strand to be copied is heated to 95C to separate the two strands, then cooled to 55C to allow the primers to anneal.

• The mixture is heated to 72C and DNA polymerase/taq polymerase builds a complementary copy of each strand of DNA.

• The process is repeated many times to produce the desired amount of DNA.

Outline what a highly conserved gene is? (1 mark)

• Gene which is common across many different organisms

Describe the role of Rubisco in photosynthesis and describe the effects of high temperatures on this process. (2 marks)

• The role of Rubisco is to fix carbon in the light-independent stage of photosynthesis.

• At high temperatures, Rubisco binds to O2 more readily than it binds to CO2, resulting in photorespiration.