Structure of Carbohydrates

  • Carbohydrates are biologically important macromolecules composed of carbon (C), hydrogen (H), and oxygen (O).
  • They are made from monosaccharides (simple sugars), with most common ones being glucose and fructose.
  • Two monosaccharides can combine to form a disaccharide (a double sugar) like sucrose, lactose, and maltose.
  • Polysaccharides are linked chains of monosaccharides forming complex carbohydrates such as starch, glycogen and cellulose.

Functions of Carbohydrates in Organisms

  • Carbohydrates serve as a key source of energy for living organisms. Glucose, for example, is the primary energy source for cells.
  • Some carbohydrates, like cellulose in plants, provide structural support. In insects and crustaceans, the carbohydrate chitin forms a major part of their exoskeleton.
  • They also play a significant role in cell recognition and signalling due to the presence of carbohydrate chains on the surface of cell membranes, aiding in cell interaction and communication.

Metabolic Pathways of Carbohydrates

  • The process by which glucose is broken down to release energy is known as glycolysis.
  • In oxygen-rich conditions, the products of glycolysis move into the Krebs cycle to produce more energy.
  • Glucose can also be stored for future use in the form of glycogen in animals and starch in plants, in a process known as glycogenesis.
  • When energy is required, these polysaccharides can be broken down into glucose through glycogenolysis in animals and starch degradation in plants.

Role of Carbohydrates in Diet and Health

  • Carbohydrates should be the body’s main source of energy in a healthy, balanced diet.
  • Eating an excess of certain types of carbohydrates, notably simple sugars, can lead to obesity and related health problems such as type 2 diabetes.
  • Fibre, a type of indigestible carbohydrate found in foods such as whole grains and vegetables, is important for maintaining a healthy digestive system.