Glycogen Metabolism

Question 1

How is glycogen synthesis favored

Answer 1

by insulin - in both liver and muscle

Question 2

What does the liver do with glycogen

Answer 2

releases as free glucose in flight or fight situation

Question 3

what does the muscle do with glycogen?

Answer 3

stores it for energy metabolism

Question 4

what regulates glycogen degradation in the liver/

Answer 4

hormones - during fasting or low insulin/glucagon ratio - glucose is released into the blood

Question 5

what is glycogen degradation linked to in skeletal muscle

Answer 5

muscle contraction - independent of hormones (you don’t wanna wait for hormones to have a contraction!) - G-6-P is used in glycolysis

Question 6

what stimulates glycogenolysis in liver and muscle?

Answer 6

epinepherine = hormone

Question 7

what takes place at the same time at low insulin levels?

Answer 7

gluconeogensis and glycogen degradation

Question 8

what happens at the same time when the muscle needs ATP

Answer 8

glycogen degradaiton and glycolysis

Question 9

when does the muscles glycogen store deplete?

Answer 9

not during fasting - during exercise!

Question 10

where is glycogen mainly found in the body?

Answer 10

largest amount = skeletal muscle

highest concentration = liver

Question 11

what can glycogen storage diseases affect?

Answer 11

liver only, or muscle only or BOTH

Question 12

what is the purpose of glycogen metabolism (2)

Answer 12

synthesis of glycogen when G-6-P is abundant - high insulin in liver and muscle

degradatino of glycogen when G-6-P is needed - low insulin in liver/muscle contraction in muscle

Question 13

in what cellular compartment is glycogen degraded and metabolized?

Answer 13

in the cytosol

glycogen is stored in cytosolic granules of liver and muscle

Question 14

what is special about glycogen metabolism?

Answer 14

many enzymes can act at the same time on glycogen because of the branched structure - tightly regulated thouhg (glycogen phophorylases vs. glycogen synthase)

Question 15

what is glycogenic?

Answer 15

core protein surrounded by branches

Question 16

what do both gylcogen syntehsis and glycogen degradation use?

Answer 16

glucose 6-P and Glucose-1-P - reversibly formed by phosphoglucomutase

Question 17

what is the highly activated form of glucose used for synthesis of glycogen? how is it made?

Answer 17

UDP-glucose

made from glucose-1-P + UTP

Question 18

what is glycogen syntheases primer needed to link UDP-glucose together

Answer 18

some branched glyogen chains that are not totally degraded - then it makes the alpha 1,4 bonds

Question 19

when alll the glycogen chains are degraded, what do we need?

Answer 19

glycogenin protein

Question 20

what does glycogenin do?

Answer 20

self-glucosylating enzyme (similar to ser and thr) uses UDP-glucose and add like 8 glucose units to its own try residue —EXCEPTION

Question 21

what is the point of having so many branches?

Answer 21

they improve solubility of glycogen

allow for accelerated rates of glycogen synthesis or degradation

Question 22

what does 4:6 transferase do?

Answer 22

removes a chain of about 8 glucosyl residues from the nonreducing end (by cleaving hte alpha 1-4 bond) and attached it to a non-temrinal glucosyl residue by an alpha 1-6 linkage

Question 23

when do you want glycogen sythase to be active?

Answer 23

insulin ruling

Question 24

what coenzyme does phosphorolytical cleavage of glycogen to G-1-P need>

Answer 24

pyridoxal phosphate (PLP) fromed from vitamin B6

Question 25

what is pyridoxal phosphate usually used for?

Answer 25

amino acid metabolism - this is an exception

Question 26

why is it important to get to a glycogen store in muscle?

Answer 26

it saves an ATP because you don’t need to convert glucose to G-6-P, you just have G-1-P and you can change it to G-6-P without using an ATP

Question 27

in both liver and muscle, how is glycogen synthease activated?

Answer 27

by glucose-6-P

Question 28

what inhibits glycogen degradation (glycogen phosphorylase) in muscle and liver?

Answer 28

glucose-6-P

ATP

Question 29

what inhibits glycogen degradation in liver only?

Answer 29

glucose

Question 30

what activates degradation in muscle only?

Answer 30

AMP (generated by muscle contraction)

Question 31

what is limit dextrin?

Answer 31

intermediate in glycogen degradation which is a substrate for debranching enzymes

Question 32

what does 4:4 transferase do

Answer 32

leads from limit dextrin to longer branches

Question 33

what does 1:6 glucosidase do?

Answer 33

cleaves the alpha 1-6 bond at the branch point and generates 1 free glucose molecule

Question 34

what does gylcogen degradation generate?

Answer 34

G-1-P and some free glucose

Question 35

what can protein kinase A only phosphorylate?

Answer 35

glycogen phosphorylase kinase

Question 36

what is glycogen phospohrylase kinase?

Answer 36

the enzyme which phosphorylates and activates glycogen phosphorylase b which makes it a

Question 37

what does glyocgen phosphorylase kinase have

Answer 37

calcium for allosteric activation and calmodulin

Question 38

what does AMP allosterically activate?

Answer 38

glycogen phophorylase

Question 39

what does glycogen synthase do (in general)

Answer 39

takes 2 UDP-glucose and smushes them together! - but it needs a primer to do that!