Ch 13.2 Gluconeogenesis + Others

What is gluconeogenesis

A pathway that converts pyruvate and related three- and four- carbon compounds to glucose

• occurs in all animals, plants, fungi and microorganisms

• mainly occurs in the liver in mammals

2 pyruvate —> glucose

Gluconeogenesis and Glycolsis

Share several steps however not indentical pathways in possite directions

• 3 glycolisis reactions are essetially irreverible and cannot be used in gluconeogensis (steps 1,3, and 10)

How is gluconeogenesis regulated

at the fructose biphosphate step by fructose 2,6-bisphosphate (F2, 6P)

• F2,6P activates glycolysis and inactivates gluconeogenesis

• No Fructose 2,6 BP, glycolsis is turned off and gluconeogenesis is turnd on

Gluconeogensis sum reaction

Cost: 2 pyruvate, 4 ATP, 2 GTP, 2 NADH

Return: Glucose, 4 ADP, 2GDP, 2NAD+

energentically expensive but essential

glycogenolysis

the breakdown of cellular glycogen to glucose 1-phopshate

glygoenesis

synthesis of glycogen

Glycogen structure

made of glucose

• highly branched a 1,6

• linear a 1,4

What does glycogen synthesis begin with

glucose-6-phosphate

sources of glucose 6-phosphate

• hexokinase makes glucose 6 phosphate from glucose

• lactate taken up by the liver is converted to glucose 6-phosphate by gluconeogenesis

phosphoglucomutase

converts glucose 6-phosphate to glucose 1-phosphate

glycogen synthesis

energy = UTP

adds glucose to extend the glycogen polymer

Glycogen branching enzyme

catalyzes the formation of the a1,6 bonds found at the branch points of glycogen

• build on glycogen core (a glycogenin protein)

what is glycogenolysis catalyzed by

glycogen phosphorylase: catalyzes phosphorolytic cleavage at the nonreducing ends of glycogen chains

• requires phosphate

• acts repetitvely until it reach a point four residues away from a a1, 6 branch point

Debracnhing enzyme

transfers branches onto main chains and relases the residue at the branch as free glucose

Phosphoglucomutase

catalyzes the reversible conversion of glucose-1-phosphate to glucose 6 phosphate

pentose phosphate pathway

purpose: alternate pathway for glucose oxidation

occurs in: cytosol of most cells

Products: Pentoses for nucleotide synthesis and NADPH for biosynthesis of fatty acids

Where does the pentose phosphate pathway come into play?

Glucose is turned into Glucose-6-phosphate and it can either continue and go into the citric acid cycle or go to the pentose phosphate pathway

Products of the pentose phosphate pathway

NADPH: used for cholesterol + fatty acid synthesis. Used for reduction of glutanione

Ribose 5 phosphate

What cycle happen is there is adequate glucose vs what happens if there is low glucose

Enough glucose: Glycolysis, glycogenesis

Low glucsoe: glyconeogenesis and glycogenolysis