Chapter 9: Carbohydrate Metabolism 1: Glycolysis, Glycogen, Gluconeogenesis and the Pentose Phosphate Pathway

GLUT 2

low affinity transporter in hepatocytes and pancreatic cells

captures excess glucose primarly for storage

GLUT 4

in adipose tissues and muscle and responds to glucose concentration in peripheral blood

Glycolysis

cytoplasmic pathway converst glucose into two pyruvate molecules, releasing energy captured in two substrate level phsophorylation and oxidation reaction

hexokiases

widely distributed in tissues and is inhibited by its product G6P

glucokinase

found in liver cells and pancreatic B islet cells

where is heoxkinases present

in most tissues

where is glucokinase present

in hepatocytes and pancreatic B ilets

PFK 1

rate limiting enzyme and main control point in glycolysis. phosphorylate F6P to F16BP activated by AMP, F26BP inhibited by ATP and citrate

3 phosphoglycerale kinase

transfer high energy phosphate from 13 PPG to ADP forming ATP and 3Phosphoglycerate

Pyruvate Kinase

activated by F16BP

feed forward activation

product of earlier reaction prepare, later reaciton in glycolysis

PFK2

produce F26BP actiavtes PFK 1, activated insulin and inhibited by glucagon

Glyveraldehyde 3 Phosphate Dehydrogenase

produce NADH, feed into electron transport chain

3 Phosphoglycerate kinase and pyruvate kinase

each perform substrate level phsophorylation, placing P1 onto ADP to form ATP

galactose

comes from lactose in milk, it is trapped in cell by galactokinase and converted to glucose 1 phosphate via galactose 1 phosphate.

Fructose

comes from honey, fruit and sucrose. It is trapped in cell by fructokinase and then cleaved by aldolase B to form glyceraldehyde and DHAP

Pyruvate Dehydrognease

refer to complex enzymes convert pyruvate to acetyl CoA

Glycogen

branced polymer of glucose

Glycogenesis

syntehsis fo glycogen granules

Glycogen synthesis

creates alpha 1,4 glycosidic links between glucose molecules. It is activated by insulin in liver and muscle

Branching enzyme

moves a block of oligoglucose form one chain and adds it to the growign glycogen as a new branc using an alpha 1,6 glycosidic

Glycogenolysis

process fo breaking down glycogen

glycogen phosphorylase

removes single glucose one phosphate molecules by breaking alpha 1,4 glycosidic links.

Debranching enzyme

moves a block of oligoglucose form one branch and connects it to the chain using an alpha 1,4 glycosidic link.

Isoforms

slightly different versions of the same protein

glycogen storage disease

disease characterized by accumulation or lack of glycogen in one or more tissues

Glucogenic amino acids

converted into intermediates that feed into glucogensis

Ketogenic amino acid

used as alternative fuel

Important substrate for gluconeogenesis

Glycerol 3 phosphate, lactate and glucogenic amino acid

Pyruvate carboxylase

converst pyruvate into oxaloacetate, which is converted by phosphoenolase pyruvate by phosphoenolpyruvate.

Fructose 1,6 biphosphatase

converts fructose 1,6 biphosphate to fructose 6 phosphate, by passing phosphofructokinase 1. This is the rate limiting step of gluconeogensis

Glucose 6 phosphotase

converst glucose 6 phosphate to free glucose, bypassing glucokinase.

Pentose Phosphate Pathway

generating NADPH and sugar for biosynthesis

Functions of NADPH

biosyntehsis fatty acid and cholesterol

Assiting cellular bleach production in certain WBC, contribute to baterial activity

Maintence of supply of reduced glutathione to protect against reactive oxygen species

Glutathione

reducing agent hlep reverse radical formation before damage is done to cell