Enzyme regulation #2

Question 1

Name 6 different types of covalent modification.

Answer 1

~ phosphorylation
~ methylatoin
~ adenylation
~ ADP-ribosylation
~ acetylation
~ ubiquitination

Question 2

Phosphorylation (4)

Answer 2

~ catalysed by kinases
~ of serine, threonine or tyrosine residues
~ often causes conformation change
~ reversible post-translational modification

Question 3

3 different results of phosphorylation

Answer 3

1. block an active site
2. O can H-bond with residues on the polypeptide
3. -ve charge on phosphate group can repel -ve charged molecules

Question 4

Phosphatase

Answer 4

enzyme that reverse phosphoylation

Question 5

Phosphorylation recognition sequences are…

Answer 5

diverse

Question 6

What regulates the enzymatic regulators?

Answer 6

~ protein kinase activity often regulated by 2nd messenger conc (e.g. cAMP)

Question 7

2nd messenger-dependent allosteric activation

Answer 7

~ activation depends of 2nd messengers

~ displacement of an auto-inhibitory sub-unit

Question 8

Insulin-dependent activation of RTK (4)

Answer 8

1. Insulin binds to dimeric tyrosine receptor kinase
2. this activates tyrosine kinase domain of each beta-subunit = autophosphorylation of 3xTyr residues
3. this fully opens the tyrosine-kinase active site of each beta-subunit
4. phosphorylation of target protein which effects metabolic enzymes + gene expression

Question 9

AMPK

Answer 9

~ AMP-activated kinase (AMPK)
~ responds to reduced [ATP] and increased [AMP]
~ [AMP] better energetic state indicator than [ATP]

Question 10

AMPK positively targets enzymes involved with…

Answer 10

~ glucose uptake
~ glycolysis
~ fatty acid oxidation
~ mitochondrial biogenesis

Question 11

AMPK negatively targets (inhibits via phosphorylation) enzymes involved with…

Answer 11

~ protein synthesis
~ glycogen synthesis
~ gluconeogenesis
~ fatty acid/cholesterol biosynthesis

Question 12

AMPK structure

Answer 12

~ a’ catalytic subunit
~ B’ adaptor subunit
~ y-sununit (AMP-binding sites)

Question 13

Which 3 mechanism activates AMPK

Answer 13

1) allosteric activation by AMP
2) AMP-dependent promotion of phosphorylation of Thr(172) by upstream kinase
3) inhibition of Thr(172) dephosphorylation

Question 14

High [ATP] + AMPK

Answer 14

high [ATP] antagonises binding of AMP = no activation

Question 15

Compartmentalization

Answer 15

regulation of enzyme activity by dynamic changes un enzyme localisation
e.g. glucokinase vs hexokinase

Question 16

no glucose + glucokinase

Answer 16

~ glucokinase binds to a regulatory protein which sequesters it int he nucleus
~ at low [glucose], glucokinase has increase affinity for regulatory protein due to +ve effector fructose-6-phosphate
~ liver does not compete with other organs for scarce glucose

Question 17

no glucose then glucose + glucokinase

Answer 17

~ an increase in intracellular glucose disrupts glucokinase regulator interaction ~ glucokinase moves into cytosol
~ liver repossess quickly to increase in blood-glucose levels