CARBOHYDRATE METABOLISM PART 3

Glycogenesis (glycogen synthesis)

building of glycogen using two main enzymes

What are the 2 main enzymes that build glycogen in glycogenesis?

-glycogen synthase

-branching enzyme

Glycogen synthase

creates alpha-1,4 glycosidic links between glucose molecules

What is glycogen synthase activated by?

insulin in the liver and muscles

What is the function of the branching enzyme in glycogenesis?

moves a block of oligoglucose from one chain and connects it as a branch

What type of glycosidic link does the branching enzyme use to connect branches in glycogenesis?

alpha-1,6 glycosidic link

Glycogenolysis

breakdown of glycogen using two main enzymes

What are the 2 main enzymes to break down glycogen in glycogenolysis?

-glycogen phosphorylase

-debranching enzyme

What does Glycogen Phosphorylase do?

removes a single glucose 1-phosphate molecules by breaking alpha-1,4-glycosidic links

How is Glycogen Phosphorylase activated in the liver?

activated by glucagon to prevent low blood sugar

How is Glycogen Phosphorylase activated in skeletal muscle?

activated by epinephrine and AMP to provide glucose to the muscle itself

What is the function of the debranching enzyme?

Moves a block of oligoglucose from one branch.

How does the debranching enzyme connect oligoglucose to the chain?

Using an alpha-1,4 glycosidic link.

What does gluconeogenesis occur?

in both cytoplasm and mitochondria, predominantly in the liver

Most of gluconeogenesis is just the reverse of glycolysis, using the same ____.

enzymes

3 irreversible steps of glycolysis must be bypassed by different enzymes:

-pyruvate carboxylase and PEP carboxykinase bypass pyruvate kinase

-fructose-1, 6-bisphosphatase bypasses phosphofructokinase-1

-glucose-6-phosphatase bypasses hexokinase/glucokinase

Which enzymes bypass pyruvate kinase in gluconeogenesis?

Pyruvate carboxylase and PEP carboxykinase

Which enzyme bypasses phosphofructokinase‑1 (PFK‑1) in gluconeogenesis?

Fructose‑1,6‑bisphosphatase

Which enzyme bypasses hexokinase/glucokinase in gluconeogenesis?

Glucose‑6‑phosphatase

Where does the Pentose Phosphate Pathway occur?

In the cytoplasm of most cells

What are the main products of the Pentose Phosphate Pathway?

NADPH and sugars for biosynthesis

What is the rate-limiting enzyme of the Pentose Phosphate Pathway?

Glucose-6-phosphate dehydrogenase

What activates glucose-6-phosphate dehydrogenase?

NADP+ and insulin

What inhibits glucose-6-phosphate dehydrogenase?

NADPH