L19 - liver in metabolism - glucose homeostasis

Question 1

roles of glucose

Answer 1

1. source of pyruvate (metabolism)
2. source of NADPH (FA synthesis, drug metabolism)
3. source of pentose sugars
4. source of carbon

Question 2

advantages of glucose as metabolic fuel

Answer 2

1. water soluble (no need for carriers)
2. can cross BBB
3. can be oxidised anaerobically

Question 3

disadvantages of glucose as fuel

Answer 3

1. relatively low yield compared to FA
2. osmotically active
3. high conc can damage cells and lead to toxic by products (fructose, sorbitol)

Question 4

role of glucose in skeletal muscle

Answer 4

energy for muscle contraction

Question 5

function of glucose in adipose tissue

Answer 5

production of glycerol phosphate to form TGs

Question 6

define gluconeogenesis

Answer 6

production of glucose from non carbohydrate sources (AAs, glycerol, lactate, pyruvate)

Question 7

what are blood glucose sources

Answer 7

diet
liver glycogen
liver gluconeogenesis

Question 8

can glucose be synthesised from fat? why /why not

Answer 8

no

pyruvate — acetyl CoA is irreversible

Question 9

what are the enzymes that catalyse the irreversible reactions of glycolysis

Answer 9

hexokinase/glucokinase
phosphofructokinase
pyruvate kinase

Question 10

how is pyruvate converted back to phosphoenol pyruvate

Answer 10

pyruvate —– oxaloacetate (pyruvate carboxylase)

oxaloacetate — phosphoenol pyruvate (PEP carboxykinase)

Question 11

what enzyme catalyses

oxaloacetate — phosphoenol pyruvate

Answer 11

PEP carboxykinase

Question 12

what enzyme catalyses

pyruvate —- oxaloacetate

Answer 12

pyruvate carboxylase

Question 13

how are
glucose — glucose 6 phos
fructose 6 phos —- fructose 1,6 bisphos
reversed

Answer 13

reactions where a phosphate is removed

Question 14

how is gluconeogenesis regulated?

Answer 14

1. providing the substrate
   -(fat breakdown - glycerol)
   -(muscle protein breakdown - AA)
2. activation of enzymes (G6Pase, PEPCK, F1,6
   bisPase)

Question 15

is high ratio of insulin:glucagon fed or fasting state?

Answer 15

fed

Question 16

is low ratio of insulin:glucagon fed or fasting state?

Answer 16

fasting

Question 17

what are the enzymes involved in gluconeogenesis

Answer 17

glucose 6 phosphatase
fructose 1, 6 bisphosphatase
pyruvate carboxylase
phosphoenol pyruvate carboxykinase

Question 18

what activates the enzymes involved in gluconeogenesis

Answer 18

G6P , F 1 6 bisPase and PEPCK activated when insulin:glucagon is low (fasting state)

pyruvate carboxylase activated by acetyl CoA

Question 19

what are the effects of insulin on the liver

Answer 19

inhibits glycogen breakdown
inhibits protein breakdown
glucose ----> glycogen promoted 
glucose -----> FA promoted
inhibits gluconeogenesis

Question 20

effects of insulin in adipocytes

Answer 20

inhibits TG breakdown

Question 21

effects of insulin in muscle

Answer 21

increased glucose uptake (more GLUT4)
glucose —-> glycogen
protein synthesis

Question 22

effects of glucagon

Answer 22

• activates glycogenolysis
• activates gluconeogenesis
• inhibits glycogen synthesis
• increases blood FAs and ketone bodies (lipolysis)(FA oxidation)
• decreases blood [AA]

Question 23

what pathway does glycerol enter for oxidation

Answer 23

glycolysis

Question 24

main role of glucose in adipose tissue

Answer 24

glycolysis producing glycerol phos for TG assembly

Question 25

role of NADPH

Answer 25

anabolic reactions eg FA synthesis

Question 26

what is cori cycle

Answer 26

recycling of lactate from muscle via conversion to glucose in liver