Enzymes 3

Question 1

Where are regulatory enzymes found

Answer 1

Rate limiting step

Question 2

what are regulatory mechanisms

Answer 2

• Allosteric activation/inhibition
• Phosphorylation or other covalent modification
• protein-protein interactions
• Proteolytic cleavage
• Synthesis

Question 3

What is allosteric regulation

Answer 3

Use of small molecules which bind to enzymes to change enzyme (not at active site) (bind reversibly. molecules are called effectors)

Question 4

What are effectors

Answer 4

Small molecules which bind to enzymes to change the enzyme (they are not substrates)

Question 5

What are homotropic effectors

Answer 5

Same as substrate

Question 6

What are heterotropic effectors

Answer 6

Not the same as substrate

Question 7

What is positive cooperativity

Answer 7

Binding allows more to bind

Question 8

What is ‘concerted’ model

Answer 8

Allosteric interactions

-adjacent subunits change from T to R state

Question 9

What is the ‘sequential’ model

Answer 9

Same as concerted model, but subunits change state one at a time

Question 10

What does phosphorylation do

Answer 10

Negatively charged so makes the compound negative and affects ionic interactions and hydrogen bond patterns

Question 11

What is protein-protein interactions

Answer 11

Small molecular proteins get close to some enzymes which then affect other enzymes

Question 12

Example of protein-protein interactions

Answer 12

• Ca2+ from sarcoplasmic reticulum binds to calmodulin-bound subunit of glycogen phosphorylase kinase
• Changed and activated
• Phosphorylates glycogen phosphorylase
• Increases ATP generation

Question 13

What is proteolytic cleavage

Answer 13

Use lysosomes or proteosomes to irreversibly activate/inactivate enzymes

Question 14

What is enzyme synthesis

Answer 14

Induction or repression leads to an alteration in the total population of active sites

Question 15

What are advantages of allosteric regulation

Answer 15

• effectors, as they bind to sites other than catalytic site, can be activators (not just inhibitor)
• Effectors do not need to resemble substrate or product
• Regulation is rapid (as soon as effector changes, effect is seen)

Question 16

What is a negative effector

Answer 16

Effector binds and enzyme activity is reduced

Question 17

What do both negative and positive effectors affect

Answer 17

Affect enzyme affinity for substrate (K0.5) and/or maximal catalytic activity (Vmax)

Question 18

What is phosphorylation mediated by?

What do they use as a phosphate donor?

Answer 18

Protein kinases

-use ATP as a phosphate donor

Question 19

How are phosphate groups removed

Answer 19

Protein phosphatases via hydrolysis

Question 20

What do protein kinases do

Answer 20

Some only regulate one protein, others simultaneously regulate several rate-limiting emzymess

Question 21

What does protein kinase A do

Answer 21

phosphorylates several enzymes that regulate different metabolic pathways

Question 22

What does adrenaline do (second messenger model)

Answer 22

• Adrenaline increases the intracellular concentration of cAMP
• cAMP binds to regulatory subunits of protein kinase A
• Causes their release, and activation of catalytic subunits

Question 23

Examples or other modifications

-What do these affect?

Answer 23

• addition/removal of acetyl, ADP-ribose, or lipids

- Affect the ability of enzymes to interact with other proteins or to reach its correct locations

Question 24

What do Monomeric proteins bind to and hydrolyse?

-What does binding lead to?

Answer 24

Guanosine Triphosphate (GTP)
-Change of conformation and so bind to target protein

Question 25

How can activity of G proteins be regulated?

Answer 25

By accessory protein (these can also be regulated by allosteric effectors)

Question 26

HOW can enzymes be irreversibly activated or inactivated?

Answer 26

By proteolytic enzymes