Carbohydrate metabolism is the biochemical process through which every carbon molecule passes through metabolism, catabolism, and interconversion in living beings. Carbohydrates are energy sources for plants and animals. Carbohydrate metabolism consists of various steps including digestion, absorption, transport, glycolysis, Krebs cycle, electron transport chain, gluconeogenesis, glycogenesis, and glycogenolysis. Through carbohydrate metabolism energy is stored in the form of ATP.

What is Carbohydrate Metabolism?

The biological process by which each different carbohydrate molecule in a living thing undergoes metabolism, catabolism, and interconversion is known as Carbohydrate Metabolism. Both plants and animals utilize carbohydrates as an energy source. Digestion, absorption, transport, glycolysis, Krebs cycle, electron transport chain, gluconeogenesis, glycogenesis, and glycogenolysis are some of the processes that make up the metabolism of carbohydrates. ATP is the kind of energy that is stored during the metabolism of carbohydrates.

Overview of Carbohydrate Metabolism

Carbohydrate Metabolism process basically involves a series of biological processes

1. Glycolysis: It occurs in cell cytoplasm, where glucose molecules breakdown into two pyruvate molecules. This process occurs in two phases.
2. Pyruvate decarboxylation: It occurs in mitochondria matrix of cell, where pyruvate molecules goes into the process of decarboxylation and form an acetyl CoA.
3. Citric acid or Krebs cycle: It occurs in mitochondrial matrix, in which carbon dioxide releases and reduced cofactors is produced by further oxidizing carbon atoms, is where acetyl-CoA enters (NADH and FADH₂). As soon as the original acetyl-CoA is completely oxidized, the cycle is over.
4. Electron transport chain (ETC): It occurs in inner membrane of mitochondria, where the electrons in the electron transport chain are donated by the NADH and FADH₂. An electrochemical gradient is produced when protons are pumped across the inner mitochondrial membrane in conjunction with electron flux. Water act as a byproduct and oxygen serves as the ultimate electron acceptor in ETC.
5. Oxidative Phosphorylation: It occurs in inner membrane of mitochondria, where adenosine diphosphate (ADP) and inorganic phosphate are converted into ATP via the electrochemical gradient created in the electron transport chain (Pi).

Metabolic Pathways of Carbohydrates

The metabolic pathways of carbohydrates includes the following phases:

Glycolysis

Glycolysis is a process in which glucose molecule breakdown to form two pyruvate molecule and energy generated in the form of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NADH). Glycolysis process occur in 10 steps and which are divided into two phases. In 1st phase Glycolysis consists of ten steps, split into two phases. It needs to break down two molecules ATP in the first phase. The chemical energy is converted into ATP and NADH during the second phase.

Regulation of Glycolysis

The regulation of glycolysis is done through following steps:

• Glycolysis process can be controlled by feedback regulation.
• Third phase of the glycolysis is extremely controlled phase.
• Controlling of phase to ensure the limited production of pyruvate molecules an to ensure that glycogen can be stored in the fatty acid form.

Gluconeogenesis

Gluconeogenesis is the process by which non carbohydrate carbon sources get converted into glucose molecules and this process occurs in both eukaryotes and prokaryotes. The primary site of gluconeogenesis in all vertebrates is cortex of kidney. Gluconeogenesis control blood sugar level and also prevents hypoglycemia. Rumen animal also tend to have gluconeogenesis inspite of low carb diet.

Glycogenolysis

Breakdown of one molecule of glucose from glycogen and formation of glucose-1-phosphate and later on conversion of glucose-1-phosphate into glucose-6-phosphate, this process is known as glycogenolysis. Organs like kidney, liver and muscles get glucose by this process. One molecule of ATP is required to form glucose from glycogen. Glucose-6-phosphate get converted to glucose in liver and kidney that leads to increase in blood sugar level. In hypoglycemia, liver start producing glucagon, which results on initiation of glycogenolysis.

Glycogenesis

Conversion of glucose into glycogen in vertebrates is known as glycogenesis. Glycogen is a highly branched structure. Due to highly branched structure, glycogen is considered to be the more soluble. Kidney, skeletal muscles, and liver are the main sites where glycogenesis happen.

Pentose Phosphate Pathway

Glucose is also present in red blood cells, testis, phagocytes, liver, adipose tissue and memory glands where oxidation glucose is procured by pentose phosphate pathway.

Fructose Metabolism

Fructose is a carbohydrate which needed to be metabolized as well. In fructose metabolism, fructose is phosphorylated by the enzymes present in kidney, adipose tissues and muscles and Later it get hydrolyzed.

Galactose metabolism

Milk sugar is known as lactose is made up of glucose and galactose. When we drink milk, lactose present in it get breakdown into galactose. In liver galactose is phosphorylated into glucose-1-phosphate by enzyme galactokinase using one ATP. Later on, glucose-1-phosphate get converted by glucose-6-phosphate by the process known as glycolysis.

Importance of Carbohydrate Metabolism

Metabolism of carbohydrate is very important to produce energy and that energy will get stored in the form of ATP to perform various biological process. Here are some importance of Carbohydrate Metabolism.

1. Production of energy: Carbohydrate metabolism work as a fuel production by breaking down of glucose molecule to perform certain functions.
2. Level up of blood glucose: Metabolism of carbohydrate helps in regulation of blood glucose level by directing cells to take up extra glucose thus resulting in decreasing of glucose level in blood.
3. Glycogen storage: Extra glucose in our body is get stored in liver in the form of glycogen and get utilized whenever there is low glucose level.
4. Maintaining of ketone bodies: Regular glucose breakdown lead to decrease in fat break down thus leading to decrease production of ketone bodies.
5. Metabolic maintainence: Carbohydrate metabolism lead to the maintainence of insulin level to prevent insulin resistance syndrome.

Disorders of Carbohydrate Metabolism

Disorder of carbohydrate metabolism are result of malfunction is the metabolism of carbohydrates. Here is the list of disorders

1. Diabetes mellitus
   1. Type 1 and 2 diabetes
2. Hypoglycemia
   1. Reactive Hypoglycemia
   2. Fasting Hypoglycemia
3. Glycogen storage disease
4. Glacatosemia
5. Fructose indigestion
6. Lactose indigestion
7. Metabolic syndrome: Insulin resistance syndrome

Also read:

• Biomolecules – Definition, Structure, Classification, Examples
• Carbohydrates – Definition, Classification, Sources, Importance

FAQ’s – Carbohydrate Metabolism

1. What are the Stages of Carbohydrate Metabolism?

Carbohydrate metabolism initiates with glycolysis, converting glucose to pyruvate. Pyruvate undergoes decarboxylation, forming acetyl-CoA. In the citric acid cycle, acetyl-CoA oxidizes, yielding NADH and FADH2, which donate electrons to the ETC, generating an electrochemical gradient driving ATP production.

2. How does the Body Metabolize Carbohydrates?

The breakdown of carbohydrates in our body results in the absorption of monosaccharides into the bloodstream. As blood sugar levels increase, the pancreas releases insulin, a hormone that facilitates the movement of sugar from the blood into cells.

3. What are the 4 Processes of Metabolism?

Carbohydrate metabolism encompasses glycolysis forming pyruvate, gluconeogenesis converting G6P to glucose, glycogenesis storing glucose as glycogen, and the pentose phosphate pathway generating NADPH for fatty acid synthesis.

4. What is Carbohydrate Metabolism and Classification?

Carbohydrates are classified into four types: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Monosaccharides, with the chemical formula C₆H₁₂O₆, represent simple sugars. Disaccharides, on the other hand, are composed of two monosaccharide units.

5. What are the 4 Main Functions of Carbohydrates?

Carbohydrates serve as an energy source, regulate blood glucose and insulin, contribute to cholesterol and triglyceride metabolism, and play a role in fermentation. Upon consumption, the digestive tract breaks down carbohydrates into glucose, providing a vital energy substrate.