A2 quesiton help (aqa past paper) BYA5

Hiya
Can anyone help me answer this from a recent aqa past paper for BYA5. We havent really been doing much yet on this section at college but Ive been looking ahead at past questions. Need help though:

9. (a) Some antibiotics bind with specific receptors in the plasma membranes of bacteria. The structure of these receptors is determined genetically. Bacteria can become resistent to an antibiotic because a gene mutation results in an altered receptor.

(i) Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation conferring resistance in just one bacterium (5 Marks)

(ii) Deletion and substitution are two types of gene mutation. Explain why a deletion is more likely to lead to a bacterium becoming resistant to an antibiotic than a substitution. (6 Marks)

Reply 1

Cirsium

Ok well if you think about it if there's a lot of antibiotic around killing all the bacteria, and one bacterium mutates or picks up a plasmid so that it has antibiotic resistance then while everything else is dying off, it can sit there happily splitting by binary fission and making lots more bacteria like itself, who all have that resistance. Because A.R. is a selective advantage, bacteria with that characteristic will become dominant in the population. Then you can get into fun fun things like conjugation and transduction

As for the second bit... hmmm let me think...

Reply 2

Aired

(ii) Deletion and substitution are two types of gene mutation. Explain why a deletion is more likely to lead to a bacterium becoming resistant to an antibiotic than a substitution. (6 Marks)

Deletion causes frame shift so that many of the codons in the gene coding for the receptor protein will be incorrect. Substitution doesn't cause frame shift so only one codon is changed (this may not actually change the amino acid that it codes for, the substitution could create a codon for the same amino acid as the original codon). Due to this, a protein coded by a gene affected by a deletion mutation will have a higher proportion of incorrect amino acids than a protein coded for by a gene affected by a substitution mutation.
For 6 marks just go into more detail about how more amino acids being changed will have a more dramatic effect on the tertiary structure of the protein and so there is more chance that the antibiotic will be unable to bind to it.