[FMS] NAM - glycogen synthesis and regulation

Question 1

what kind of molecule is glycogen

Answer 1

polysaccharide

Question 2

how much glycogen is in tissue stores compared to the liver

Answer 2

400g in tissue

100-200 in liver

Question 3

what kind of osmolarity does glycogen have

Answer 3

low osmolarity

Question 4

what kind of fuel store is glycogen

Answer 4

medium-term fuel store

Question 5

what 2 things control the liver

Answer 5

The liver is sensitive to blood glucose concentration under the control of insulin and glucagon

Question 6

What is role of glycogen in muscle fuel for exercise?

Answer 6

Glycogen in the muscle does not go to glucose when breaking it down unlike in the liver.

Glycogen goes to glucose-6-phosphate which goes into glycolysis for energy for contraction.

Question 7

What is the physiological significance of glycogen-branched structure?

Answer 7

More points of contact for enzymes to act on.

Question 8

what are the 4 important parts of glycogens structure

Answer 8

Question 9

What are the two types of linkages in glycogen?

Answer 9

• alpha-1,4-glycosidic linkage - makes linear chains
• alpha-1,6-glycosidic linkage - makes branched chains

Question 10

What are 3 features of biosynthetic pathways?

Answer 10

• ATP or UTP or GTP are needed as cofactors (to ‘drive the reactions forward’)
• one or more enzyme reactions will be irreversible, and alternative enzymes are used for the ‘opposite direction’
• enzyme reactions at the beginning or end of the pathway are tightly regulated

Question 11

how is glycogen synthesised, including enzymes etc

Answer 11

Question 12

how is glycogen broken down, including enzymes etc

Answer 12

Question 13

outline the coordinated regulation of synthesis/ breakdown in liver

Answer 13

Question 14

outline the coordinated regulation of synthesis/ breakdown in muscles

Answer 14

Question 15

what happens during muscular contraction

Answer 15

• During muscular contraction, calcium ions are released into the sarcoplasmic reticulum.
• Calcium binds the calmodulin domain of glycogen phosphorylase kinase and activates the enzyme
• This in turn activates the phosphorylase and glycogen is degraded providing energy for contracting muscle

Question 16

What are the controls in prolonged exercise?

Answer 16

• In prolonged exercise, ATP concentrations are reduced and AMP concentrations begin to rise.
  
  • AMP is an allosteric activator of glycogen phosphorylase.
  • Glycogen degradation continues without the need for hormonal interaction ATP is an allosteric inhibitor, so that when energy levels are high, glycogen breakdown stops.

Question 17

what are the 3 glycogen storage diseases?

Answer 17

“Von Gierke’s Very Enlarged Liver due to Glucose-6-Phosphatase”

Pompe’s Poorly Pumps Muscles and Cardiac due to Lysosomal Glycosides”

“McArdle’s Muscles Must Manage (with) Limited Energy due to Glycogen Phosphorylase

Question 18

whats the function of AMP in glycogen synthesis

Answer 18

allosteric activator of glycogen phosphorylase

Question 18

How is glycogen synthase regulated?

Answer 18

BY PHOSPHORYLATION (Glycogen synthase is inactivated by phosphorylation)

Question 19

whats the function of ATP in glycogen synthesis

Answer 19

allosteric inhibitor, so when energy levels are high, glycogen breakdown stops

Question 20

What is the difference between a phosphatase, phosphorylase and kinase?

Answer 20

phosphatase removes phosphate and phosphorylase hydrolyses and uses inorganic phosphate. And a kinase phosphorylates using the high-energy phosphate compound ATP.

Question 21

what enzyme breaks a-1,6 glycosidic bonds between glucose units

Answer 21

DEBRANCHING ENZYME via hydrolysis

Question 22

what enzyme breaks a-1,4 glycosidic bonds between glucose units

Answer 22

glycogen phosphorylase

Question 23

in the first step of glycogen synthesis, what is the difference between when hexokinase is used, and when glucokinase is used?

Answer 23

hexokinase in all other tissue

glucokinase in liver ONLY

^BECUASE Hexokinase has a low Km so is able to do this reaction in low glucose concentrations, glucokinase has a high Km So glucokinase is used in the liver because it is a store and you don’t want it all to be used up.

Question 24

what stimulates and inhibits insulin

vs

what stimulates and inhibits glucagon

Answer 24

Insulin stimulates glucose uptake and utilization while inhibiting glucose synthesis and breakdown.

Glucagon stimulates glucose synthesis and breakdown while inhibiting glucose uptake and glycogen synthesis.

Question 25

Phosphorylation of what enzyme stops glycogen synthesis - glycogen synthase or glycogen synthase kinase?

Answer 25

Glycogen synthase is the enzyme directly involved in glycogen synthesis, and its activity is inhibited when it is phosphorylated by glycogen synthase kinase (GSK).

So, the phosphorylation of glycogen synthase by GSK stops glycogen synthesis.

Glycogen phosphorylase is the enzyme directly involved in glycogen breakdown, and its activity is inhibited when it is phosphorylated by glycogen phosphorylase kinase (GPK).

So, the phosphorylation of glycogen phosphorylase by GPK stops glycogen breakdown.

therefore answer is GLYCOGEN SYNTHASE KINASE

Question 26

what activates protein kinases?

Answer 26

cAMP