Carbohydrate Metabolism and Regulation Revision

Carbohydrate Metabolism and Regulation Revision

Catabolic Reaction Pathways

1.Glycolysis/Glycogeneolysis

2.Citric Acid Cycle

Anabolic Reaction Pathways

1. Gluconeogenesis

2. Glycogenolysis

Glucose is stored as glycogen in the liver after taking in a carbohydrate rich meal, excess is stored as triacylglycerol in the adipose tissue. How Carbohydrates are metabolised for energy involves two stages which are Glycolysis and Citric Acid Cycle.

1. Glycolysis is the formation of 2 pyruvate molecules from a single glucose molecule. This step is mainly regulated by the enzyme phosphofructokinase and this stage utilises ATP.

2. Citric Acid cycle is where the glucose molecule will undergo oxidative phosphorylation linked with the electron transport chain to form ATP.

3. Gluconeogenesis is process of making glucose and this occurs when the blood sugar levels are low

How are carbohydrates metabolized after 30 minutes into exercise

Glucagon still remain fairly high in liver

Glycogen needs to be converted to glucose (glycogenolysis)

Glycogen ------> glucose 1 phosphate -------> glucose 6 phosphate ----> Glucose (transported in blood stream to enter muscle for glycolysis)

Glucose converted to Pyruvate

Pyruvate converted to acetyl CoA which enters Krebs Cycle to undergo oxidative phosphorylation to produce ATP.

Glycolysis Produces a net of 2 ATP

Krebs cycle and electron transport chain together produce 34 ATP

Regulation of Carbohydrate Metabolism

Can be regulated in 4 ways :

1. Concentration of substrate and enzyme

2. Allosteric Regulation by ATP - after exercise ATP levels are low as most of them are phosphorylated and exists as AMP, so Phosphofructokinase enzyme is relieved if ATP, therefore it is active

3. Hormones- Glucagon and Insulin

4. Transcription Regulation- such as enyzmes for glycolysis

Regulation of Glycolysis

Phosphofructokinase is the main regulating enzyme

Phosphofructokinase activation and inhibition