L7A: Glycogen Catabolism & L7B: Glucose and Glycogen Synthesis

Question 1

what are the most significant contributors to the feeder pathway into glycolysis (glycogen catabolism)

Answer 1

The storage polysaccharides, glycogen & starch

Question 2

what is glycogen

Answer 2

v/ large polymer of glucose with alpha 1-4 and alpha 1-6 linkages

Question 3

what kind of linkages in glycogen

Answer 3

alpha 1-4 and alpha 1-6 linkages

Question 4

how many tiers are in mature glycogen

Answer 4

12 tiers - with 55,000 glucose residues

Question 5

function of glycogen

Answer 5

• stored during meals & released during the day
• NB in maintaining blood glucose concentration

Question 6

where is glycogen stored in animals

Answer 6

liver and skeletal muscle

Question 7

function of glycogen stored in the liver

Answer 7

• liver glycogen = glucose reservoir
• supplies glucose to blood/tissues when dietary glucose low

Question 8

function of muscle glycogen

Answer 8

• quick source of energy
• used in less than 1 hr during vigorous activity

Question 9

enzyme in step 1 of glycogen catabolism

Answer 9

glycogen phosphorylase (GP)

Question 10

function of glycogen phosphorylase in step 1 of glycogen catabolism

Answer 10

removes terminal glucose residues from non reducing end by phosphorylysis

Question 11

what happens in step 1 of glycogen catabolism

Answer 11

glycogen phosphorylase adds a phosphoryl group to terminal glucose to form glucose-1-phosphate and lyse it off glycogen

Question 12

what enzyme is involved in step 2 of glycogen

Answer 12

debranching enzyme

Question 13

what happens in step 2 glycogen catabolism

Answer 13

• GP acts repetitively until it meets alpha 1-6 branch
• GP stops working 4 glucose residues before branch
• transferase activity of debranching enzyme removes 3 glucose residues
• alpha 1-6 glucosidase activity of debranching enzyme cuts off glucose
• left w an unbranched alpha 1-4 polymer

Question 14

in step 2 glycogen catabolism, when does GP stop

Answer 14

GP stops working 4 glucose residues before alpha 1-6 branch

Question 15

what does glycogen catabolism result in lots of

Answer 15

glucose-1-phosphate

Question 16

what enzyme converts G-1-P to G-6-P

Answer 16

phosphoglucomutase

Question 17

outcome of glycogen catabolism in liver

Answer 17

• G-1-P converted to G-6-P
• into liver
• phosphate removed in liver by glucose-6-phosphatase
• glucose goes into blood
• transported to tissues that need it
• fed into glycolysis to produce energy

Question 18

outcome of glycogen catabolism in muscle

Answer 18

• G-6-P in muscle
• into glycolysis step 2
• produces energy

Question 19

glycogen storage diseases: genetic mutations occur in what

Answer 19

1. glycogen phosphorylase
2. glycogen debranching enzyme
3. glucose-6-phosphatase

Question 20

what do glycogen storage diseases result in

Answer 20

• enlarged liver
• muscle wasting - myopathy
• metabolic problems

Question 21

tx of glycogen storage diseases

Answer 21

• low glucose & monitored carbohydrate diet
• gene replacement therapy

Question 22

when does glucose need to by synthesised

Answer 22

when glycogen/starch is depleted & there is no dietary input

Question 23

where does gluconeogenesis occur

Answer 23

• liver cytosol
• renal cortex
• small intestine cells

Question 24

what are the main 3C glucose precursors

Answer 24

• lactate
• pyruvate
• glycerol

Question 25

what are the main 4C glucose precursors

Answer 25

* glucogenic amino acids - especially alanine & glutamine * citric acid cycle intermediates - especially oxaloacetate

Question 26

what does gluconeogenesis share w glycolysis

Answer 26

the 7 reversible steps

Question 27

which steps in gluconeogenesis have different exergonic regulated enzymes

Answer 27

* Step 1 - conversion of pyruvate to phosphoenolpyruvate * Step 7 - conversion of fructose 1,6-bisphosphate to fructose-6-phosphate * Step 10 - conversion of glucose-6-phosphate to glucose

Question 28

the bypass rxn in step 10 gluconeogenesis

Answer 28

* converts glucose-6-phosphate to the glucose enzyme, glucose-6-phosphatase * this removes the phosphoryl group at position 1

Question 29

the bypass rxn in step 7 gluconeogenesis

Answer 29

* converts fructose 1,6-bisphosphate to fructose-6-phosphate enzyme, fructose 1,6-bisphosphatase * this removes phosphoryl group at position 1

Question 30

the bypass rxn in step 1 gluconeogenesis

Answer 30

* converts pyruvate to phosphoenolpyruvate * needs 2 enzymes: 1) pyruvate carboxylase 2) PEP carboxykinase * needs energy: 2xATP, 2xGTP for 2 pyruvate

Question 31

what 2 enzymes does step 1 gluconeogenesis need

Answer 31

1. pyruvate carboxylase 2. PEP carboxykinase

Question 32

how does gluconeogenesis cost energy

Answer 32

makes 1 glucose from 2 pyruvates using 4ATP, 2GTP and 2NADH

Question 33

what cells does glycogen synthesis mainly occur in

Answer 33

liver & skeletal muscle cells

Question 34

what is the enzyme in step 1 glycogen synthesis

Answer 34

phosphoglucomutase

Question 35

what happens in step 1 glycogen synthesis

Answer 35

G-6-P isomerised to G-1-P, catalysed by phosphoglucomutase

Question 36

what happens in step 2 glycogen synthesis

Answer 36

* UDP nucleotide added to glucose-1-phosphate * G-1-P + UTP -> UDP-Glucose + PPi

Question 37

enzyme in step 3 glycogen synthesis

Answer 37

glycogen synthase

Question 38

what happens in step 3 glycogen synthesis

Answer 38

* UDP-Glucose donates glucose to non reducing end of growing glycogen chain * catalysed by glycogen synthase - major regulated enzyme in glycogen synthesis

Question 39

enzyme in step 4 glycogen synthesis

Answer 39

glycogen branching enzyme

Question 40

what happens in step 4 glycogen synthesis

Answer 40

* glycogen branching enzymes make alpha 1-6 branches * glycogen synthesis starts on a protein "primer" called glycogenin