Biomolecules: Carbohydrates and Lipids – Structure and Function

Carbohydrates

Overview of Carbohydrates

Carbohydrates are essential organic molecules that include sugars and starches. They serve as a primary energy source for most living organisms and play structural roles in cells and tissues.

• Composition: Contain carbon (C), hydrogen (H), and oxygen (O), typically in a 2:1 ratio of hydrogen to oxygen.

• Classification: Carbohydrates are classified into three main groups based on the number of sugar units:

  • Monosaccharides: Single sugar units (monomers).

  • Disaccharides: Composed of two monosaccharide units.

  • Polysaccharides: Polymers made up of many monosaccharide units.

Monosaccharides

Monosaccharides are the simplest carbohydrates, consisting of three to seven carbon atoms. They are the building blocks (monomers) of more complex carbohydrates.

• General Formula: $(CH_2O)_n$ where n is the number of carbon atoms.

• Types:

  • Pentose sugars (5 carbons): Ribose and deoxyribose (important in nucleic acids).

  • Hexose sugars (6 carbons): Glucose (blood sugar), fructose, and galactose.

• Function: Serve as a quick source of energy and as structural components in cells.

• Example: Glucose is the primary energy source for cellular respiration.

Disaccharides

Disaccharides are formed by the chemical joining of two monosaccharides through a dehydration synthesis reaction (removal of water).

• Examples: Sucrose (glucose + fructose), maltose (glucose + glucose), lactose (glucose + galactose).

• Properties: Too large to pass through cell membranes without being broken down.

• Formation Reaction:

  • $\text{glucose} + \text{fructose} \rightarrow \text{sucrose} + \text{water}$

Polysaccharides

Polysaccharides are large, complex carbohydrates composed of long chains of monosaccharide units linked by glycosidic bonds. They are formed by repeated dehydration synthesis reactions.

• Examples:

  • Starch: Storage form of carbohydrates in plants.

  • Glycogen: Storage form of carbohydrates in animals (mainly in liver and muscle cells).

• Properties: Not very soluble in water; serve as energy reserves.

• Function: Provide long-term energy storage and structural support.

Table: Examples of Carbohydrate Molecules Important to the Body

Type	Example	Function
Monosaccharide	Glucose, Fructose, Galactose, Ribose, Deoxyribose	Energy source, building blocks for nucleic acids
Disaccharide	Sucrose, Maltose, Lactose	Transported sugars, must be digested to monosaccharides
Polysaccharide	Starch, Glycogen	Energy storage in plants and animals

Lipids

Overview of Lipids

Lipids are a diverse group of hydrophobic organic molecules that include fats, oils, and related compounds. They are insoluble in water and serve as important energy reserves, structural components, and signaling molecules.

• Composition: Contain C, H, O (less O than carbohydrates), and sometimes phosphorus (P).

• Main Types: Triglycerides, phospholipids, steroids, eicosanoids.

Triglycerides

Triglycerides, also known as fats (solid) or oils (liquid), are the most common type of lipid in the body. They are composed of three fatty acids attached to a glycerol molecule via dehydration synthesis.

• Structure: 1 glycerol + 3 fatty acids.

• Main Functions:

  • Energy storage

  • Insulation

  • Protection of organs

• Example: Adipose tissue stores triglycerides for energy and insulation.

Additional info:

• Triglycerides are formed by the process of esterification, where each fatty acid forms an ester bond with the glycerol backbone.