Lecture 20 - Biological Molecules IIII

Question 1

transition state mimemics;

Answer 1

• The enzyme will stabilize the transition state to make the cleavage reaction more favourable
• We can make things that look like the transition state so fit the active site but don’t get hydrolysed

Question 2

Enzyme Acid-Base Catalysis:

Answer 2

• Amino acid functional groups can act as bases or acids to help reactions progress

• This is important as there are often few water molecules available at the active site to do this

• Histidine, glutamic acid and aspartic acid can all be involved in acid / base reactions

Question 3

Nucleophilic Groups:

Answer 3

• Many enzymes contain serine and cysteine at their active sites

• These residues are nucleophilic and can get involved in the reaction mechanism

• Normally, serine OH (pKa 16) isn’t nucleophilic

• Other close by residues can help though. Nearby histidine and aspartate can form a catalytic triad, helping it be more nucleophilic

Question 4

Chymotrypsin:

Answer 4

a digestive enzyme that cleaves peptide chains where the N-terminal side is a large hydrophobic amino acid residue and is a serine protease

Question 5

what conditions does chymotrypsin cleave amides bonds in?

Answer 5

it manages to cleave the bond at a neutral pH at 37C

Question 6

what assists hydrolysis in the protease chymotrypsin?

Answer 6

cooperativity of the catalytic triad assists the hydrolysis

Question 7

beta-lactams:

Answer 7

• Certain moulds produce B-lactams that kill certain bacteria. These are the penicillins

• B-lactams inhibit transpeptidases in cell wall synthesis

• The B-lactam is more like a ketone or ester than an amide due to the ring strain in the 4-membered ring

Question 8

transpeptidase:

Answer 8

transpeptidase is a bit like a protease: it has to hydrolyse a peptide so that it can cross link it to make the cell wall

Question 9

B-lactamases antibiotic resistance:

Answer 9

• Some bacteria have evolved to become resistant to B-lactams

• They produce B-lactamase enzymes that hydrolyse penicillins rendering them useless

• We have responded (in one way) by developing B-lactamase inhibitors eg clavulanic acid

Question 10

what do b-lactams inhibit?

Answer 10

B-lactams inhibit bacterial cell wall production