L8- Regulation of metabolic pathways

Question 1

where does glycolysis occur

Answer 1

in the cytoplasm of all tissues

Question 2

how can glycolysis operate anaerobically

Answer 2

LDH

• production of NADH (reducing powers) meaning glycolysis can continue
• e.g. in RBC, muscles etc

Question 3

allosteric means

Answer 3

other site

Question 4

enzyme shave two sites

Answer 4

catalytic site

regulatory site

Question 5

catalytic site

Answer 5

substrate binding

Question 6

regulatory site

Answer 6

binding of specific regulatory molecules

• affects catalytic activity
• can activate or inhibit

Question 7

allosteric regulation cause

Answer 7

covalent modification e.g. phosphorylation/ dephosphorylation

Question 8

covalent modification e.g. phosphorylation/ dephosphorylation

Answer 8

alters protein conformation and therefore activity

Question 9

pathways are regulated by

Answer 9

irreversible steps

Question 10

with irreversible steps reduced activity reduces the rate of flow of..

Answer 10

substrates through the pathway directly, reducing levels of product

Question 11

with reversible steps, even when inhibited

Answer 11

reactions still come to equilibrium so levels of product unaffected

Question 12

product inhibition

Answer 12

where the product displaces the equilibrium towards the substrate
- reduces rate of catalysis of substrate to product

Question 13

feedback inhibitor

Answer 13

where final product inhibits first enzyme in pathway

- reduces entry of substrate into the pathway leading to build up of intermediates

Question 14

committing step

Answer 14

inhibition of committing step allows substrate to be diverted into other pathways

Question 15

regulation of enzymes can be

Answer 15

inhibitory or stimulatory

Question 16

catabolic pathways such as glycolysis and the kerb cycle are inhibited

Answer 16

by high energy signals such as ATP, NADH and FAD2H

Question 17

catabolic pathways such as glycolysis and the kerb cycle are stimulated by

Answer 17

low energy signals such as o ADP, AMP, NAD+, FAD+

Question 18

hormonal regulation

Answer 18

hormone receptor binding can activate signalling pathways e.g. insulin (tyrosine kinase receptor)
- this can activate Protein kinases (phosphorylation) or phosphates (dephosophorylation)

Question 19

phosphorylation/ dephospho rylation of target enzyme

Answer 19

alters protein conformation/ activity positively or negatively depending on the target enzyme

Question 20

example of phosphorylation: adrenaline

Answer 20

adrenaline binds to GPCR
o Activates protein kinase A
o Phosphorylation activates phosphorylase kinase
o Phosphorylation of glycogen phosphorylase
i. Stimulates glycogen break down

Question 21

example of phosphorylation: insulin

Answer 21

Insulin binds to TK receptor
o Stimulated signalling pathway activates protein phosphatase 1
o Dephosphorylates/activates pyruvate dehydrogenase
i. Stimulates glucose utilisation
o Dephosphorylates glycogen phosphorylase
i. Inhibits glycogen breakdown

Question 22

feed forward

Answer 22

• Early pathway substrate provides positive allosteric signal to stimulate a later enzyme to activate the pathway

Question 23

name the 3 key regulators of glycolysis

Answer 23

1. Hexokinase (glucokinase in the liver) (1)
2. Phosphofructokinase-1 (3)
3. Pyruvate kinase (10)

Question 24

hexokinase

Answer 24

Product inhibition by Glucose-6-P

 Enzyme activity will reduce as more glucose is catalysed to glucose-6-p- negative regulator

Question 25

phosphofructokinase-1 (PFK) is the most

Answer 25

important enzyme in the regulation of glycolysis

Question 26

how can PFK regulate glycolysis

Answer 26

allosteric regulation (muscle) hormonal regulation (liver)

Question 27

PFK and allosteric regulation (muscle)

Answer 27

o Inhibited by high ATP | o Stimulated by high AMP

Question 28

PFK and hormonal regulation (liver)

Answer 28

o Stimulated by insulin | o Inhibited by glucagon

Question 29

Pyruvate kinase

Answer 29

regulated via phosphoregulaton - final stage of glycolysis

Question 30

when glucagon (starvation hormone) binds to its receptor

Answer 30

protein kinase A conc in the cell increases and this phosphorylated ADP--> ATP ( low energy signal) -INHIBITING GLYCOLYSIS

Question 31

when insulin (well fed hormone) binds to it receptor

Answer 31

protein phosphatase 1 conc increases and this dephosphorylates ATP--> ADP (high energy signal) - STIMUALTING GLYCOLYSIS

Question 32

hexokinase is inhibited by

Answer 32

glucose-6-phosphate (its own product) - therefore PRODUCT INHIBITION

Question 33

high ATP ....... PFK

Answer 33

inhibits

Question 34

high AMP ....... PFK

Answer 34

stimulates

Question 35

where is the commuting step in glycolysis

Answer 35

phosphofructokinase

Question 36

high insulin and low glucagon will

Answer 36

stimulate glycolysis by causing enzyme depths (more high energy signals such as ADP)