Carbohydrate metabolism

Carbohydrate Metabolism

Carbohydrate metabolism is the whole of the biochemical processes responsible for the metabolic formation, breakdown, and interconversion of carbohydrates in living organisms. Carbohydrates are central to many essential metabolic pathways. Plants synthesize carbohydrates from carbon dioxide and water through photosynthesis, allowing them to store energy absorbed from the sunlight internally.

Overview

Carbohydrates are the most abundant biomolecule on Earth. Living organisms use carbohydrates as accessible energy to fuel cellular reactions and for structural purposes. Additionally, the carbon that makes up most of the dry weight of plants is derived from carbohydrates. Carbohydrates are also involved in the immune system, the development of disease, blood clotting, and reproduction.

Carbohydrate Catabolism

Carbohydrate catabolism is the breakdown of carbohydrates into smaller units. The body’s preferred method of energy production is glycolysis, a process that breaks down glucose to form pyruvate through a series of enzymatic reactions. The production of ATP from glucose has two phases: the preparatory phase and the payoff phase.

Glycogenesis and Glycogenolysis

Glycogenesis is the process of glycogen synthesis, in which glucose molecules are added to chains of glycogen for storage. This process is activated during rest periods following the Cori cycle, in the liver, and also activated by insulin in response to high glucose levels.

Glycogenolysis is the breakdown of glycogen to glucose-6-phosphate and glycogen. Glycogen branches are catabolized by the sequential removal of glucose monomers via phosphorolysis, removing a glucose residue and forming glucose 1-phosphate.

Gluconeogenesis

Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids. It is one of the two main mechanisms humans and many other animals use to keep blood glucose levels from dropping too low.

Pentose Phosphate Pathway

The pentose phosphate pathway is a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses (5-carbon sugars) as well as ribose 5-phosphate, the latter a precursor for the synthesis of nucleotides.

Regulation

The regulation of carbohydrate metabolism involves hormonal and enzymatic pathways. Key hormones in this regulatory process include insulin, glucagon, and epinephrine.

See Also

• Metabolism
• Lipid metabolism
• Protein metabolism
• Energy metabolism