Metabolic Pathways: Glycogen

Question 1

glycogenesis

Answer 1

synthesis of glycogen from glucose

Question 2

glycogenolysis

Answer 2

breakdown of glycogen to form glucose

Question 3

gluconeogenesis

Answer 3

de novo synthesis of glucose from metabolic precursors

lactate, amino acids, glycerol

Question 4

what is glycogen

Answer 4

main storage form of glucose in liver and muscle cells

Question 5

liver glycogen

Answer 5

broken down between meals and released to maintain blood glucose levels fro red blood cells and brain

Question 6

muscle glycogen

Answer 6

not available for maintenance of blood glucose levels

provides energy via glycolysis and the TCA during bursts of physical activity

Question 7

sources of blood glucose

Answer 7

glyogenolysis fluctuates dependent upon meal times

gluconeogenesis is the primary source of glucose overnight when hepatic glycogen is depleted

Question 8

glycogenin

Answer 8

glycogen primer containing at least 4 glucose residues is covalently attached to protein

allows glucose residues to be added to existing glycogen chain

Question 9

glycogen synthesis

Answer 9

ATP required

glycolysis

Question 10

UDP-glucose

Answer 10

activated intermediate form of glucose

phosphate ester linkage in a nucleotide sugar releases free energy on hydrolysis

Question 11

glycogen synthase

Answer 11

synthesises glycogen from UDP-glucose

adds one glucose molecule to glycogen at a time

can only extend the chains of glycogen - can’t start new molecules

can not introduce branches

rate limiting enzyme of glycogenesis

branching enzyme, transglycosylase, introduces Alpha 1-6 glycosidic branches

Question 12

glycogenolysis

Answer 12

catalysed by glycogen phosphorylase

rate limiting step of glycogenolysis
one glucose molecule is cleaved of the ends of glycogen at a time

glucose-1-phosphate — glucose-6-phosphate

Question 13

glycogenolysis - in liver

Answer 13

glucose-6-phosphate can be de-phosphorylated and the resulting glucose released into the blood stream

Question 14

glycogenolysis - skeletal muscle

Answer 14

glucose-6-phosphate cannot be de-phosphorylated but instead is used to provide energy via glycolysis and the TCA cycle

Question 15

glycogenolysis - debranching

Answer 15

requires additional enzymes

Question 16

gluconeogenesis

Answer 16

synthesis of glucose within the body from precursor substrates

essentially the reverse of glycolysis

requires four unique liver enzymes

proceeds via the synthesis of oxaloacetate in mitochondria

energy consuming - energetically expensive
ATP hydrolysis drives an unfavourable reaction

Question 17

glycolysis

Answer 17

three irreversible reactions - hexokinase, phosphofructokinase, pyruvate kinase

several special reactions are required to bypass the irreversible reactions

Question 18

cori cycle

Answer 18

lactate is a precursor of gluconeogenesis - formed in fast-twitch muscle under conditions of heavy exercise

blood transports lactate to liver
liver converts lactate back to glucose
glucose released into bloodstream
buys time and shifts metabolic burden from muscle to other organs

Question 19

precursors for gluconeogenesis

Answer 19

amino acids

Question 20

reciprocal regualtion

Answer 20

glycolysis and gluconeogenesis

hormonal regualtion - glucagon and insulin

Question 21

glycogen storage diseases

Answer 21

groups of diseases with increased glycogen deposits in liver/muscle

+10 different types - defects in different enzymes