Biomolecules: Structure, Types, and Functions

Biomolecules

Introduction to Biomolecules

Biomolecules are essential organic molecules found in all living organisms. The food we eat contains these important biological molecules, which are broken down and reassembled by our bodies to perform vital functions. The four main classes of biomolecules are carbohydrates, lipids, nucleic acids, and proteins.

• Carbohydrates: Provide energy and structural support.

• Lipids: Store energy, form membranes, and act as signaling molecules.

• Nucleic acids: Store and transmit genetic information.

• Proteins: Perform a wide range of functions including catalysis, structure, and regulation.

Carbohydrates

Overview and Functions

Carbohydrates are organic molecules commonly found in foods such as bread, dairy, and vegetables. They are a primary source of energy for the body and also provide dietary fiber, which aids in digestive health.

• Monosaccharides (simple sugars) are the building blocks of carbohydrates.

• Common examples include glucose (the most common monosaccharide), lactose (milk sugar), fructose (fruit sugar), and sucrose (table sugar).

• Carbohydrates can be classified based on the number of sugar units: monosaccharides, disaccharides, and polysaccharides.

Monosaccharides

Monosaccharides are the simplest form of carbohydrates, consisting of single sugar units. They follow a 1:2:1 ratio of carbon, hydrogen, and oxygen (C:H:O), typically represented as $C_nH_{2n}O_n$ (e.g., glucose: $C_6H_{12}O_6$).

• Monosaccharides are named with the suffix -ose (e.g., glucose, fructose).

• Based on their carbonyl group, they are classified as aldoses (aldehyde group) or ketoses (ketone group).

Disaccharides

Disaccharides are formed when two monosaccharides join together via a glycosidic bond. While monosaccharides can exist in linear or ring forms, they typically adopt a ring structure in aqueous solutions.

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

• Glycosidic bonds are covalent bonds formed by a dehydration reaction.

Polysaccharides

Polysaccharides are long chains of monosaccharide units linked by glycosidic bonds. They serve as energy storage or structural components in organisms.

• Starch: Energy storage in plants; composed of branched glucose polymers.

• Cellulose: Structural component of plant cell walls; indigestible by humans.

• Glycogen: Energy storage in animals; highly branched glucose polymer.

• Chitin: Structural component in fungi and arthropod exoskeletons.

Note: Most animals cannot break down cellulose due to the lack of appropriate enzymes.

Lipids

Overview and Functions

Lipids are nonpolar hydrocarbons that are hydrophobic (water-fearing) and do not dissolve in water. They are found in various forms such as fats, phospholipids, and steroids, and serve multiple functions in living organisms.

• Form biological membranes (e.g., cell membranes).

• Store energy efficiently.

• Provide insulation and waterproofing.

• Serve as signaling molecules (e.g., hormones).

Structure of Lipids

Most lipids are composed of two main parts: a hydrophilic glycerol backbone and one or more hydrophobic fatty acids. These components are joined by an ester linkage.

• Triglycerides: Consist of glycerol and three fatty acids; main form of fat storage in animals.

• On food labels, fats are classified as saturated, unsaturated, or trans fats.

Types of Lipids

• Saturated fats: No double bonds; typically solid at room temperature; found in animal products; considered less healthy.

• Unsaturated fats: One or more double bonds; usually liquid at room temperature; found in plants and fish; considered healthier.

• Trans fats: Unsaturated fats with trans double bonds; behave like saturated fats; associated with negative health effects.

Phospholipids and Steroids

• Phospholipids: Major component of cell membranes; consist of two fatty acids, a glycerol, and a phosphate group; amphipathic (hydrophilic head and hydrophobic tails).

• Steroids: Characterized by four fused rings; include hormones (e.g., estradiol, testosterone) and cholesterol.

• Cholesterol: Essential for membrane structure but excess can lead to heart disease.

Type of Lipid	Main Structure	Function	Example
Triglyceride	Glycerol + 3 fatty acids	Energy storage	Animal fat, vegetable oil
Phospholipid	Glycerol + 2 fatty acids + phosphate	Cell membrane structure	Phosphatidylcholine
Steroid	Four fused rings	Hormones, membrane component	Cholesterol, testosterone

Additional info: The notes continue with nucleic acids and proteins, but these slides focus on carbohydrates and lipids. For a complete study guide, include nucleic acids and proteins as well.