carbohydrate metabolism

Question 1

what does the pancreas do?

Answer 1

secretes hormone insulin into blood in response to an increase in blood glucose

Question 2

why do we need to maintan blood glucose levels?

Answer 2

as glucose is a primary fuel source of brain cells via glycolysis and neurotransmitter synthesis

Question 3

how much glucose is consumed in a normal diet per day?

Answer 3

300g

Question 4

what happens when glucose enters the blood?

Answer 4

some taken up by liver via facilitated transport (uptake) stores 80-100g

insulin activates hexokinase/glucokinase to store glucose as glycogen (glycogen synthesis)

liver hexokinase reaction reversible so glucose can leave liver cell to maintain blood glucose (glycogenolysis and gluconeogenesis)

Question 5

describe most remaining glucose being taken up by skeletal muscle?

Answer 5

glucose enters muscle via facilitated transport stores up to 400-700g

hexokinase (glucokinase in liver) phosphorylates glucose using ATP to maintain gradient

glucose-6-phosphate is formed and can’t leave cell so enters glycolysis or glycogen synthesis

Question 6

what is glucose transported via in skeletal muscle intake?

Answer 6

GLUT4 (maintained hours after exercise)

which is translocated to plasma membrane from intracellular vesicles in response to insulin, muscle contraction and Ca2+ (main)

Question 7

what occurs in glycogen synthesis?

4 steps

Answer 7

glucose-6-phosphate converted to glucose-1-phosphate (G1P) by phosphoglucomutase

uridine diphosphate (UDP) glucose is synthesised from G1P and uridine triphosphate

UDP glucose binds to pre-existing glycogen molecule or glycogenin &UDP released

glycogen synthase and branching enzymes form proglycogen which grows into macroglycogen

Question 8

what is glycogenin?

Answer 8

enzyme involved in converting glucose to glycogen

situated at core of glycogen molecule

Question 9

what stimulates glycogen synthesis?

Answer 9

insulin

Question 10

what is the purpose of glycogen synthesis?

Answer 10

glucose molecules added to chain of glycogen for storage

=glycogenesis

Question 11

what reduces glycogen synthesis?

Answer 11

muscle contraction/exercise

Question 12

what is glycogenolysis and what inhibits it?

Answer 12

glycogen breakdown into glucose for utilisation (opposite of glycogenesis)

insulin

Question 13

what stimulates glycogenolysis ?

Answer 13

(glycogen breakdown)

muscle contraction/exercise

Question 14

which process is preferential during exercise?

Answer 14

glycolysis (breaking down glucose into usable ATP in liver and skeletal muscle)

Question 15

what are the main signals stimulating glycogenolysis?

Answer 15

(breaking down of glycogen)

calcium and adrenaline (high rates during high contraction in exercise)

Question 16

what reduces with exercise?

Answer 16

insulin

Question 17

what is G6P derived from?

Answer 17

glycogenolysis and glucose uptake

Question 18

where ensures blood glucose is maintained during postabsorptive period and during fasting?

Answer 18

liver as acts as a reserve

Question 19

what has to happen when glycogen reserve is exhausted in liver?

Answer 19

glucose must be made from non-carbohydrate precursors (lactate, amino acids and glycerol) via gluconeogenesis

Question 20

what increases during fasting?

Answer 20

circulating fatty acuds and glycerol

Question 21

why can’t fatty acids be used as pre-cursors?

Answer 21

pyruvate dehydrogenase and pyruvate kinase reactions are irreversible (acetyl-CoA from fatty acids can’t form glucose)

Question 22

what is gluconeogenesis?

Answer 22

conversion of pyruvate (made from non-carbohydrate precursors) to glucose

Question 23

what important role does Acetyl-CoA play?

Answer 23

inhibiting pyruvate dehydrogenase and diverting pyruvate to oxaloacetate and malate

Question 24

when is lactate produced at high rates?

Answer 24

during exercise in muscle and in red blood cells

Question 25

what is pyruvate kinae inhibited by?

Answer 25

alanine (amino acid)

Question 26

what can the liver dephosphorylate?

Answer 26

glucose-6-P

Question 27

where is glycerol released from?

Answer 27

adipose tissue

Question 28

what rate is the liver and gut releasing glucose at rest?

Answer 28

liver - 0.1g/min | gut - 1.5g/

Question 29

what rate is glucose taken up from the blood in the brain?

Answer 29

0.1g/min (same rate as released from liver)

Question 30

what is the relationship between exercise intensity and rate of glucose uptake?

Answer 30

the heavier the intensity, the higher the rate of glucose uptake by skeletal muscle e.g in leg (1g/min so 10x increase than normal)

Question 31

what happens during heavy exercise to blood glucose release and uptake levels? how is this resolved?

Answer 31

blood glucose levels will fall as release rate slower than uptake rate (needs 2g/min) so rate of glycogenolysis increases as well as glucose output from liver and stores in skeletal muscles used (as adrenaline inhibits insulin production which normally inhibits glucose output)

Question 32

why does higher exercise intensity lead to increased glycogen broken down?

Answer 32

higher rate of exercise, high turnover of ATP = high concentration of AMP = activates glycogen phosporylase = greater rate of glycogen broken down

Question 33

when does carbohydrate oxidation decline and why? how to solve this?

Answer 33

carbohydrate oxidation declines after prolonged period of exercise due to depleted glycogen sources ingest carbohydrates to increase/maintain blood glucose levels and therefore carbohydrate oxidation

Question 34

how can you delay muscle glycogen use during exercise and therefore prolong exercise and maintain glucose levels?

Answer 34

ingest carbohydrate electrolyte solution (any carb)

Question 35

what is the maximum carbohydrate oxidation rate faciliatated through 1 type and several types of CHO ingestion?

Answer 35

can't oxidise more than 1-1.2g/min unless you ingest different types of CHO together

Question 36

describe glycogen loading?

Answer 36

depleting muscle glycogen stores then glycogen loading straight after, then lack of CHO, then loading a few days before competition can increase overall glycogen levels due to increase in insulin sensitivity in muscles

Question 37

when is glycogen resynthesis highest?

Answer 37

few hours post exercise

Question 38

what is glycogenesis?

Answer 38

conversion of glucose to glycogen to be stored in the liver | = glycogen synthesis

Question 39

what effect would an increase in glycogenolysis have on glucose uptake and why?

Answer 39

uptake would decrease as large amount of glucose-6-phsophate present from glycogenolysis (breakdown of glycogen to glucose) increased levels inhibit hexokinase so less glucose uptake in cell

Question 40

what are the effects of the drug antimycin A?

Answer 40

inhibitor of cytochrome C causes ATP synthesis and oxidative phosphorylation to be inhibited