Metabolism of carbohydrates

The metabolism of carbohydrates is the process of transport, breakdown, synthesis and conversion of carbohydrate molecules. Carbohydrates are biomolecules composed of carbon (C), hydrogen (H) and oxygen (O) elements. It is the main component required by our body to perform its regular activities. About 45 to 65% of carbohydrates are ingested by an average person. All of these carbohydrates must be broken down in order to provide energy to our bodies. Generally, glucose serves as the main component of carbohydrate metabolism. In this blog, we will learn in detail about the classification of carbohydrates, glycogen metabolism, and carbohydrate metabolism biochemistry.

Classification of carbohydrates:

Based on the number of carbon atoms, Carbohydrates are classified into the following types. They are:

• Monosaccharides: It is composed of a single sugar molecule. 

1. Aldoses: Glucose
2. Ketoses: Fructose

• Oligosaccharide: It is made up of two to ten sugar molecules. Based on the number of sugar molecules it is named disaccharides, trisaccharides, tetrasaccharides, etc. Eg: sucrose, raffinose, stachyose. 
• Polysaccharides: This is made up of more than ten sugar molecules. It is classified into two types. They are:

1. Homopolysaccharides: They are composed of the same type of sugar. Eg: starch, cellulose, glycogen. 
2. Heteropolysaccharides: It is composed of different types of sugar. Eg: heparin, hyaluronic acid. 

• Derivatives: They are carbohydrates derived from different sources. Some of them are:

1. Polyols: sorbitol, mannitol
2. Amino sugars: glucosamine, galactosamine
3. Deoxy sugars: deoxyribose 
4. Sugar acids: ascorbic acid, galacturonic acid. 

Carbohydrate metabolism pathways:

Metabolism of carbohydrates occurs in the following pathways listed below. 

• Glycolysis: This is otherwise called the Embden-Meyerhof pathway. This involves the conversion of glucose to pyruvate and lactate.
• Citric acid cycle: This is also referred to as the Krebs cycle or tricarboxylic acid cycle. In this process, acetyl CoA is oxidized to CO₂.
• Gluconeogenesis: This is the process of production of amino acids, glycerols from glucose. 
• Glycogenesis: In this pathway, glycogen is produced from glucose.
• Glycogenolysis: It is the process of glycogen breakdown. 
• Hexose monophosphate shunt: It can also be called a pentose phosphate pathway or direct oxidative pathway. It is an alternative pathway for the TCA cycle and glycolysis.
• Uronic acid pathway: It is an alternative oxidative pathway for glucose that involves the conversion of glucuronic acid to glucose.
• Galactose metabolism: It involves the production of lactose and the conversion of glucose to galactose. 
• Fructose metabolism: It involves the oxidation of fructose. 
• Amino sugar and mucopolysaccharide metabolism: It involves the synthesis of mucopolysaccharides and glycoproteins.

Glycogen metabolism:

The inactive form of glucose is called glycogen. It is stored in the muscles and liver for use when needed. Two common pathways involved in glycogen metabolism are:

• Glycogenesis
• Glycogenolysis

Organs involved in carbohydrate metabolism:

Metabolism of carbohydrates occurs in different organs and parts of the body. Specific organs in carbohydrate metabolism biochemistry are:

• Liver: The liver is the central organ that performs metabolism. Glycolysis, HMP shunt and glycogenesis occur at a higher rate. Decreased gluconeogenesis pathway. 
• Adipose tissue: It is the storehouse of energy. Glucose absorption is higher at this site. Glycolysis and hexose monophosphate shunt occur commonly. 
• Skeletal muscle: Glucose assimilation is higher and glycogen production is increased. 
• Brain: Glucose acts as an energy provider for the brain. 120g of carbohydrates, generally glucose, is consumed by the brain per day. 

Carbohydrate metabolism biochemistry:

The metabolism of carbohydrates is a biochemical process that requires the involvement of various enzymes and cofactors. Some of the enzymes involved in carbohydrate metabolism are aldolase, hexokinase, amylase, fructokinase, invertase, sucrose synthase, glucose-6-phosphate dehydrogenase, phosphoglucoisomerase, ADP-glucose pyrophosphorylase, etc. NAD+, FAD, NADH, FADH2 and cobalamin are some of the cofactors involved in carbohydrate metabolism. 

Importance of carbohydrate metabolism:

The metabolism of carbohydrates plays a major role in directing the functions of our body. Some of them are:

• They serve as an important storehouse of energy. 
• They precede the function of other biomolecules.
• They serve as the basis of cellular constituents.
• It directs the function of different organs. 
• It stimulates enzyme activity.
• Carbohydrate metabolism aids hormonal secretions.
• It plays a major role in the structural development of the body. 
• They ensure development and growth. 
• It helps in brain functions. 

Disorders of carbohydrate metabolism:

Disruption in carbohydrate metabolism can result in myriad disorders. Some of the common carbohydrate metabolism disorders are diabetes, galactosemia, McArdle syndrome, obesity, Hurler syndrome, hereditary fructose intolerance, kidney failure, Morquio syndrome, cardiovascular disease, dental caries, gastrointestinal disease, Hunter syndrome and other organ dysfunctions. 

Conclusion:

The carbohydrates in the food we consume must be metabolized as they play a major role in providing energy to the body. The metabolism of carbohydrates is the fuel provider for the functions of our body. Each cell in the body requires glucose to carry on its regular activities. Proper proceedings of the carbohydrate metabolism pathway are required to lead to a healthy system. Malfunctions in those processes can result in severe health implications. Recent research has applied this carbohydrate metabolism to numerous fields of development, like medicine, health, cytology, oncology, etc.