enzymes II

Question 1

what is a perfect enzyme?

Answer 1

→enzyme that catalyses a reaction so efficiently that the rate-limiting step is that of substrate diffusion into the active site.

Question 2

what is an example of a ‘perfect’ enzyme?

Answer 2

→Triosephosphate isomerase (TIM).
→catalyses the conversion of Dihydroxyacetone Phosphate & Glyceraldehyde 3-Phosphate (the two 3C intermediates in glycolysis)

Question 3

how do perfect enzymes work?

Answer 3

→ instead of there being a big energy change and the reaction happening by conversion of A to Z

→it happens via intermediates that don’t have a high energy change between them, making the conversion easier.

→The reaction is limited by E + S (substrate diffusion into the enzyme), so decreasing the energy levels doesn’t increase the efficiency/rate of reaction.

Question 4

how do serine proteases work? (give an example including where it is made)

Answer 4

→Chymotrypsin has a very reactive serine group which attacks the peptide bond to form an acyl-enzyme.

→Chymotrypsin (and Trypsin) are made in the pancreas.

Question 5

what is the catalytic triad?

Answer 5

→Ser 195 may get its reactivity due to its positioning next to His 57 and Asp 102.

→This is a catalytic triad, which makes the serine much more electronegative.

→ triad is found in all proteases.

Question 6

how does trypsin work?

Answer 6

→cleaves after Lys, Arg (which are positively charged), due to its negative pocket/cleft

Question 7

how does chymotrypsin work?

Answer 7

→cleaves after Phe, Trp, Tyr (which are aromatic and hydrophobic) due to its hydrophobic pocket/cleft

Question 8

how does elastase work?

Answer 8

→cleaves after small amino acids (with a small R group) due to its narrow pocket/cleft.

Question 9

how does ATP synthesis occur in a mitochondrion?

Answer 9

→ occurs via a proton-driven rotary ATP Synthase.

→ because the inner membrane of the mitochondrion is impermeable to ATP.

Question 10

how does ATP synthase work?

Answer 10

→ATP Catalysis begins when protons pass through the part of the enzyme that lies in the cell membrane, causing it to turn.

→The central core then rotates inside the top half of the enzyme.

→this region holds an ATP molecule and pulls in ADP and an inorganic phosphate group in the neighbouring subunit.

→As the core rotates, the subunit with ATP loosens, and the section holding ADP closes.

→The original ATP molecule is released, and a new one is formed from the ADP.

→ The cycle repeats.

Question 11

how does topoisomerase II work?

Answer 11

→The G-segment (gate segment) of the chromosome binds to the Topoisomerase II.

→ ATP is used to clamp the T-segment (target segment) of the chromosome.

→ The G-segment is broken, and the T-segment is pulled through.

→The G-segment is resealed and released via ATP hydrolysis.