Lecture 9 - Enzyme kinetics

Question 1

example of enzymes being stereospecific

Answer 1

usually glucose switches from its aldehyde state to alpha and beta usually

but during synthesis of cellulose, only B form is selected for by enzyme

Question 2

what is delta G’º

Answer 2

diff between the substrates and products (ratio of S to P
- if it’s negative, then product is favoured as energy is released
- never affected by enzyme

Question 3

what is delta G‡

Answer 3

activation energy
determines reaction rate
energy needed to get to TS‡

Question 4

what is TS‡

Answer 4

transition state of the reaction
can only be reached with activation energy

Question 5

what is the active site most complementary to

Answer 5

for transition state
which allows transition state stabilisation

Question 6

what is the proximity effect

Answer 6

enzyme bringing together subsrtaetes and makes them more liekly to react

Question 7

what are the 2 ways the AAs in the active site can influence catalysis

Answer 7

• bind via non-covalent interactions with the substrate
• some AAs have catalytic functional groups
  e.g. - ionisible side chains
• groups that can form covalent bonds to the substrate (nucleophiles/electrophiles)
  or
• metals (cofactor)

Question 8

what are the 2 types of enzyme cofactors

Answer 8

• metal ions (loose bound or tightly bound - metalloezymes)
• coenzymes (transient carriers of atoms/functional groups)

Question 9

2 types of coenzymes

Answer 9

• cosubstrates = loosely bound, recycled (e.g. ATP, coA)
• prosthetic groups = coenzyme is tightly bound to enzyme (e.g. haem)

Question 10

what is the rate equation for enzymes

Answer 10

Δ[P] / Δ t = v = k[S]
v being velocity/rate of reaction
k is a rate constant specific to reaction

Question 11

what is first order

Answer 11

linear direct correlation
so V0 = k[S]

Question 12

what is zero order

Answer 12

when enzyme added
and it gets to a point conc of substrate doesnt matter
since all active sites are occupied

Question 13

what is the fastest step in two step enzyme reaction scheme

Answer 13

E + S <-> ES
fast and reversible

Question 14

what is the slowest step in two step enzyme reaction scheme

Answer 14

ES -> E + P
ie the catalytic step

Question 15

what is kcat

Answer 15

the catalytic constant
only at when enzymes are fully saturated
for simple reactions it’s = to k2
kcat=vmax/[Et]

Question 16

what is the specificity constant

Answer 16

kcat/km
can measure both kcat and km and then calculate using that equation
and it can be used to compare diff enzymes
(higher the result=the better the enzyme

Question 17

oxidoreductases

Answer 17

aka dehydrogenases
catalyse redox reactions

Question 18

transferases

Answer 18

catalyze group transfer reactions

Question 19

hydrolases

Answer 19

catalyse hydrolysis reactions
so it’ll cleave a bond and add water to the products

Question 20

lyases

Answer 20

catalyse lysis
cleave off a group leaving a double bond
(NOT a redox reaction or hydrolysis)

e.g. decarboxylases, aldolases, dehydratases

some will do the reverse reaction (adding to a double bond) = synthases

Question 21

isomerases

Answer 21

caltalyse isomerism reactions
no change in molecular formula
only changes the structure

Question 22

ligases

Answer 22

catalyse joining of two substrates
forming new covalet bond
unlike these, needs chemical energy e.g. ATP