Biological Molecules

Introduction to Biological Molecules

Biological molecules are essential compounds that form the structure and function of all living organisms. Most biological molecules are polymers, which are long chains made from repeating smaller units called monomers. Cells synthesize a vast array of large molecules from a relatively small set of simple building blocks.

• Polymers: Large molecules composed of repeating monomer units.

• Monomers: The basic building blocks of polymers.

• Major classes: Carbohydrates, lipids, proteins, and nucleic acids.

Classes of Large Biological Molecules

Overview of the Four Major Classes

There are four main classes of large biological molecules, each with distinct structures and functions:

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids

Carbohydrates, proteins, and nucleic acids are typically polymers, while lipids are not true polymers but are large and complex molecules.

Carbohydrates

Structure and Types

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, usually in a ratio of 1:2:1. They serve as energy sources and structural materials in cells.

• Monosaccharides: Simple sugars (e.g., glucose, fructose) that are the monomers of carbohydrates.

• Disaccharides: Two monosaccharides joined together (e.g., sucrose, maltose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose).

Monosaccharides can be classified by the number of carbon atoms (trioses, pentoses, hexoses) and by the type of carbonyl group (aldoses or ketoses).

• Aldoses: Monosaccharides with an aldehyde group (e.g., glucose).

• Ketoses: Monosaccharides with a ketone group (e.g., fructose).

Polysaccharides serve as energy storage (starch in plants, glycogen in animals) or structural components (cellulose in plants, chitin in fungi and arthropods).

Lipids

Structure and Types

Lipids are a diverse group of hydrophobic molecules that are not true polymers. They include fats, phospholipids, and steroids.

• Fats: Composed of glycerol and fatty acids; function as energy storage molecules.

• Phospholipids: Major components of cell membranes, consisting of a glycerol backbone, two fatty acids, and a phosphate group.

• Steroids: Lipids with a characteristic four-ring structure (e.g., cholesterol, hormones).

Fatty acids can be saturated (no double bonds) or unsaturated (one or more double bonds), affecting the physical properties of fats.

Proteins

Structure and Function

Proteins are polymers made from 20 different amino acids. The sequence of amino acids determines a protein's structure and function. Proteins perform a wide variety of roles in cells, including catalysis (enzymes), defense (antibodies), transport (hemoglobin), signaling (hormones), and structural support (collagen).

• Primary structure: The linear sequence of amino acids in a polypeptide chain.

• Secondary structure: Local folding patterns such as alpha helices and beta sheets, stabilized by hydrogen bonds.

• Tertiary structure: The overall three-dimensional shape of a polypeptide, determined by interactions among side chains.

• Quaternary structure: The association of multiple polypeptide chains to form a functional protein.

Protein structure can be disrupted by changes in temperature, pH, or other environmental factors, leading to denaturation and loss of function. Proper folding is often assisted by chaperone proteins (chaperonins).

Nucleic Acids

Structure and Function

Nucleic acids store and transmit genetic information. The two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Nucleic acids are polymers of nucleotides, each consisting of a five-carbon sugar, a phosphate group, and a nitrogenous base.

• DNA: Stores genetic information; composed of adenine (A), thymine (T), cytosine (C), and guanine (G).

• RNA: Involved in protein synthesis; contains uracil (U) instead of thymine.

The sequence of nitrogenous bases encodes genetic information. In DNA, A pairs with T and C pairs with G via hydrogen bonds. In RNA, A pairs with U and C pairs with G.

Genomics and Proteomics

Emerging Fields in Biology

Genomics and proteomics are fields that study the complete set of DNA (genome) and proteins (proteome) in an organism, respectively.

• Genomics: Involves sequencing, analyzing, and comparing genomes to understand genetic relationships, evolution, and disease.

• Proteomics: Studies the full set of proteins expressed by a genome, including their structures, functions, and interactions.

Applications include identifying genetic risk factors for disease, tracing evolutionary relationships, and discovering new species.

Summary Table: Major Classes of Biological Molecules

Key Equations and Concepts

• Dehydration synthesis: The process by which monomers are joined to form polymers, releasing water.

• Hydrolysis: The process by which polymers are broken down into monomers by the addition of water.

Additional info: Some context and explanations have been inferred and expanded for clarity and completeness, based on standard General Biology curriculum.