case 5 - teach me physiology carbohydrate metabolism

Question 1

where does 80% of the monosaccharide load absorbed by the small intestine go

Answer 1

this 80% is comprised of glucose, which is then delivered to the hepatocytes by the portal vein.

Question 2

what is glucose converted to and what by

Answer 2

Glucose is converted to glucose-6-phosphate by glucokinase

Question 3

what is glucose-6-phosphate converted to and what by

Answer 3

Glucose-6-phosphate is converted to glucose-1-phosphate by phosphoglucomutase

Question 4

what is glucose-1-P converted to and what by

Answer 4

Glucose-1-P is then converted to UDP-Glucose by uridyl transferase

Question 5

what happens to the UDP glucose

Answer 5

it is then added to the long glycogen chain within the liver cells by glycogen synthase, with assistance from branching enzyme

Question 6

where does glycogenlysis occur

Answer 6

within the cytosol of the liver and also within the cytosol of the skeletal muscle

Question 7

what are the steps in glycogenolysis (3)

Answer 7

Firstly, a molecule of glucose is phosphorylated to remove it from the glycogen chain by glycogen phosphorylase (assisted by debranching enzyme) creating glucose-1-phosphate

Glucose-1-phosphate is converted to glucose-6-phosphate by phosphoglucomutase

Glucose-6-P is converted to glucose by glucose-6-phosphatase

Question 8

what can glucose-6-phosphatase also do at this point

Answer 8

can alsoo enter the glycolysis pathway at this point, which culminates in the formation of pyruvate

Question 9

what happens to the freed glucose

Answer 9

it will undergo glycolysis to produce pyruvate, which is then converted into acetyl-CoA before entering the TCA cylce

Question 10

what is the difference between metabolism of glycogen i the skeletal muscle and the liver

Answer 10

in the skeletal muscle, glucokinase predominates in place of hexokinase during the first steps of glycogenesis

Question 11

what is the allosteric regulation of glycogenesis

Answer 11

the key regulatory enzyme in glycogenesis is glycogen synthase.

its activity is upregulated by high levels of glucose-6-phosphate

Question 12

what is the key regulatory enzyme in allosteric regulation of glyconeogenesis

Answer 12

In glycogenolysis, the key regulatory enzyme is glycogen phosphorylase. It is allosterically inhibited by high levels of ATP, glucose-6-phosphate and glucose.

Question 13

what hormones control the rate and direction of glycogen metabolism

Answer 13

glucagon, adrenaline and insulin

Question 14

what do glucagon and adrenaline lead to

Answer 14

up regulation of adenylate cyclase, which converts ATP to cAMP, cAMP then activates cAMP dependent protein kinase, which phosphorylates glycogen synthase and glycogen phosphorylase

Question 15

what does phosphorylation then lead to

Answer 15

deactivation of glycogen synthase and activation of glycogen phsophorylase