enzymes 3

Question 1

enzyme regulation

Answer 1

necessary as their are thousand enzymes at work at any one time
increase or decrease in activity to maintain metabolic effectiveness

Question 2

metabolic flux

Answer 2

controlling the movement through the enzymes

Question 3

rate limiting

Answer 3

slowest step of a metabolic pathway is the most efficient control point of pathway
regulates enzyme
controlled by mechanisms that affect the catalytic site

Question 4

2 basic methods of control

Answer 4

substrate response and product inhibition
substrates present: around km value to have a speedy effect
products may be bind to the catalytic sites to prevent more activity

may not be effective with long divergent pathways

Question 5

regulatory mechanisms

Answer 5

• Allosteric activation/inhibition
• Phosphorylation (or other covalent modification)
• Protein-Protein interactions
• Proteolytic cleavage

Question 6

allosteric regulation

Answer 6

activity modulation via reversible non covalent binding of small molecules(effectors bond at allosteric site)
allosteric effector binding changes catalytic site conformation
composed of multiple sub-units: catalytic, regalatory
process is rapid an first response of cells to condition changes

Question 7

advantages of allosteric regulation

Answer 7

effectors can be activators (effector binds and enzyme activity increases) and inhibitors (effector binds and enzyme activity decreases )
effectors do not need to resemble substrate or product
regulation is rapid
both affect enzyme affinity for the substrate km0.5 and/or maximal catalytic activity (Vmax)

Question 8

homotrophic effectors

Answer 8

substrates serve as an allosteric effector

usually a positive effector

Question 9

heterotropic effectors

Answer 9

the effector is different from the substrate

Question 10

co-operarivity

Answer 10

when a substrate binds one subunit and enhances the catalytic properties of other sub-units= positive
when substrates bind a subunit and it reduces catalytic activity of other subunits=negative

Question 11

the concerted model

Answer 11

1st substrate molecule ahs difficulty binding as all sub-units are in the T state conformation
on binding the subunit adjacent subunits change t high affinity (relaxed r state)
allosteric activators increase the fraction of enzyme from T to R state

Question 12

the sequential model

Answer 12

instead of influencing all other sub units, the sub unit that binds only influences one other subunit
inhibitors will maintain the sub units in a stabilised T-state
need increased substrate or activator to increase this

Question 13

covalent modification

Answer 13

lead to conformational changes
phosphorylation:
addition of phosphate group on serine, threonine,t yrosine residues
mediated by protein kinases uses ATP as a phosphate donor and the to remove them protein phosphatases

Question 14

protein kinase a

Answer 14

it has an active and inactive form = persuaded to move from one to the other by an allosteric activator
acts on several rate limiting enzymes

Question 15

covalent modification

Answer 15

phosphorylation: phosphoralysed forms may be more or less active than unphosphorylated
other modifications addition/removal of acetyl,ADP-Ribose or lipids

Question 16

protein-protein interactions

Answer 16

direct protein-protein interaction can lead to conformational change