Biological Molecules: Structure, Function, and Importance in Anatomy & Physiology

Biological Molecules

Overview

Biological molecules, also known as biomolecules, are essential compounds that form the structure and carry out the functions of living organisms. The four major classes are carbohydrates, lipids (fats), proteins, and nucleic acids. Each class has unique properties, structures, and roles in the body.

Characteristics of Biological Molecules

Key Features

• Principal Elements: Most biomolecules are composed primarily of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sometimes phosphorus (P) and sulfur (S).

• Ratio of Elements: The ratio of these elements varies by molecule type (e.g., carbohydrates typically have a 1:2:1 ratio of C:H:O).

• Special Functional Groups: Specific groups of atoms (functional groups) confer unique chemical properties and reactivity to biomolecules.

Functional Groups

Common Functional Groups in Biomolecules

• Hydroxyl (-OH): Found in alcohols; increases solubility in water.

• Carbonyl (C=O): Found in aldehydes and ketones; important in sugars.

• Carboxyl (-COOH): Characteristic of carboxylic acids; acts as an acid.

• Amino (-NH2): Found in amines and amino acids; acts as a base.

• Phosphate (-H2PO4): Found in organic phosphates; important in energy transfer (e.g., ATP).

• Sulfhydryl (-SH): Found in thiols; important for protein structure (disulfide bonds).

Monomers and Polymers

Building Blocks of Biomolecules

• Monomer: A small subunit that serves as a building block for larger molecules.

• Polymer: A large molecule made by joining many monomers together via covalent bonds.

• Condensation (Dehydration) Reactions: Monomers are joined to form polymers by removing a molecule of water.

• Hydrolysis: Polymers are broken down into monomers by adding water.

• Solubility: Many biological molecules are water-soluble, which is important for their function in cells.

Polymerization and Depolymerization

Dehydration Synthesis

Dehydration synthesis (condensation) is the process by which two monomers are covalently bonded together with the removal of a water molecule.

• Example Equation:

$C_6H_{12}O_6 + C_6H_{12}O_6 \rightarrow C_{12}H_{22}O_{11} + H_2O$

• Example: Formation of sucrose from glucose and fructose.

Hydrolysis

Hydrolysis is the reverse process, where water is added to break the covalent bond between monomers in a polymer.

• Example Equation:

$C_{12}H_{22}O_{11} + H_2O \rightarrow C_6H_{12}O_6 + C_6H_{12}O_6$

• Example: Breakdown of sucrose into glucose and fructose.

Summary Table: Major Classes of Biological Molecules

Class	Monomer	Polymer	Principal Elements	Key Functions
Carbohydrates	Monosaccharide	Polysaccharide	C, H, O	Energy storage, structure, cell recognition
Lipids	Fatty acids, glycerol	Triglycerides, phospholipids, sterols	C, H, O (sometimes P, N)	Energy storage, membranes, hormones
Proteins	Amino acid	Polypeptide	C, H, O, N (sometimes S)	Enzymes, structure, transport, signaling
Nucleic Acids	Nucleotide	DNA, RNA	C, H, O, N, P	Genetic information, protein synthesis

Additional info:

• Functional groups determine the chemical reactivity and interactions of biomolecules, which is crucial for their biological roles.

• Dehydration synthesis and hydrolysis are fundamental to the metabolism and turnover of biological macromolecules in living systems.