Enzymes

Question 1

Action of enzymes (4)

Answer 1

1. they are globular proteins
2. they are biological catalysts
3. They can be intra or extracellular
4. They reduce activation energy (amount of energy required for a chemical reaction to start) to speed up ROR

Question 2

How enzymes reduce activation energy (2)

Answer 2

1. if two substrates need to be joined: the enzyme holds the substrate molecules close together, reducing any repulsion between the molecules so they can bond more easily
2. for breakdown reaction: fitting into the active site puts a strain on bonds in the substrate so the molecules break up more easily

Question 3

lock and key (3)

Answer 3

1. substrate is a complementary shape to the active site.
2. as it binds, the active site changes shape slightly to fit the substrate more closely
3. E+S, ESC, EPC, E+Ps

Question 4

temp affecting enzymes (3)

Answer 4

1. increased temp = more KE so molecules move faster so collisions are more likely
2. energy of collisions increases so a reaction is more likely
3. when temp rises, molecules vibrate more so if temp goes too high then vibrations break the bonds that hold the enzyme in shape, changing the shape of the active site so substrate no longer can fit. Enzyme is denatured

Question 5

pH affecting enzymes (2)

Answer 5

1. enzymes have optimum pH (usually pH 7 in humans)
2. above and below the optimum, H+ and OH- ions mess up the ionic and Hydrogen bonds in the tertiary structure, changing the shape of the active site

Question 6

Enzyme concentration affecting enzymes (2)

Answer 6

1. the more enzyme molecules, the more likely a substrate is to collide with one to form an ESC
2. so ROR increases unless amount of substrate is limited

Question 7

Substrate concentration affecting enzymes (3)

Answer 7

1. more substrate = faster reaction as collisions more likely
2. only up to a saturation point when all active sites are full
3. initial rate = highest because substrate conc decreases with time

Question 8

Cofactors and Coenzymes (3)

Answer 8

1. some cofactors are inorganic molecules or ions. They help the enzyme and substrate bind together. (not used up or changed in any way)
2. some cofactors are organic molecules called coenzymes. they participate in the reaction and are changed by it
3. a prosthetic group is a tightly bound cofactor (becomes a permanent part of the active site)

Question 9

Inhibition (2)

Answer 9

1. competitive - similar shape to substrate and compete with the substrate to bind to AS. No reaction takes place, they just block the AS so no substrate can fit in (cause they are proper rude)
2. non-competitive - bind to the allosteric site and change the shape of the AS so the substrate can no longer bind and increasing substrate conc will have no difference

Question 10

reversible or not (2)

Answer 10

1. strong covalent bonds = inhibitor cant be removed easily so the inhibition is irreversible
2. weaker H-bonds or weak ionic bonds = inhibitor can be removed and the inhibition is reversible

Question 11

Metabolic pathways x end product inhibition (3)

Answer 11

1. a series of connected metabolic reactions. The product of the 1st reaction takes part in 2nd etc…
2. Each reaction is catalysed by an enzyme - many are inhibited by the product of that reaction (product inhibition)
3. End product inhibition is where the final product inhibits an enzyme that acts earlier on