Macromolecules and Their Biological Importance: Study Notes for General Biology

Macromolecules in Biology

Introduction to Macromolecules

Macromolecules are large, complex molecules essential for life, found in all living organisms. They are typically polymers, formed by joining smaller units called monomers. The four main categories of biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids.

• Carbohydrates: Energy storage and structural support

• Lipids: Energy storage, insulation, and cell membrane structure

• Proteins: Enzymatic activity, structure, transport, and more

• Nucleic acids: Storage and transmission of genetic information

Organic Compounds and Functional Groups

Organic Compounds

Organic compounds are molecules primarily composed of carbon atoms bonded with hydrogen, oxygen, nitrogen, and other elements. Carbon's ability to form four covalent bonds makes it uniquely suited to form diverse and complex molecules.

• Example: Methane ($CH_4$) is a simple organic molecule with one carbon atom bonded to four hydrogens.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. They behave similarly in different molecules and are key to the diversity of organic chemistry.

• Examples: Hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), phosphate (-PO4)

Formation and Breakdown of Macromolecules

Polymerization and Monomers

Macromolecules are formed by linking monomers through chemical reactions:

• Dehydration Reaction (Condensation): Joins two monomers by removing a molecule of water.

• Hydrolysis: Breaks polymers into monomers by adding water, essentially the reverse of dehydration.

Carbohydrates

Overview

Carbohydrates are organic molecules made of carbon, hydrogen, and oxygen, typically with a hydrogen:oxygen ratio of 2:1. They serve as a primary energy source and as structural components in cells.

• General formula: $C_n(H_2O)_n$

Monosaccharides (Simple Sugars)

Monosaccharides are the simplest carbohydrates and cannot be broken down into smaller sugars. They are the monomers of carbohydrates.

• Examples: Glucose, fructose (both $C_6H_{12}O_6$)

• Isomers: Molecules with the same molecular formula but different structures (e.g., glucose and fructose)

Disaccharides

Disaccharides are formed by joining two monosaccharides via a dehydration reaction.

• Examples: Lactose (milk sugar), maltose (beer, malted milk), sucrose (table sugar)

• General formula: $C_{12}H_{22}O_{11}$

Polysaccharides

Polysaccharides are complex carbohydrates made of long chains of monosaccharide units. They serve as energy storage or structural materials.

• Starch: Energy storage in plants (polymer of glucose)

• Glycogen: Energy storage in animals (polymer of glucose)

• Cellulose: Structural component in plant cell walls; most abundant organic compound on Earth; indigestible by animals

Lipids

Overview

Lipids are a diverse group of hydrophobic molecules, including fats, oils, phospholipids, and steroids. They are not true polymers but are assembled from smaller molecules.

• Hydrophobic: Lipids do not mix well with water.

• Functions: Energy storage, insulation, cell membrane structure, signaling

Fats (Triglycerides)

Fats are composed of glycerol and three fatty acids, joined by dehydration reactions.

• Saturated fats: No double bonds in fatty acid chains; solid at room temperature; mostly animal fats

• Unsaturated fats: One or more double bonds; liquid at room temperature; mostly plant oils

• Hydrogenation: Process of converting unsaturated fats to saturated fats by adding hydrogen

Steroids

Steroids are lipids with a structure of four fused carbon rings. They function as hormones and structural components.

• Cholesterol: Key component of cell membranes; precursor for steroid hormones (e.g., estrogen, testosterone)

• Synthetic anabolic steroids: Variants of testosterone; can mimic its effects

Proteins

Overview

Proteins are polymers made of amino acid monomers. They perform a vast array of functions, including catalysis (enzymes), structure, transport, and signaling.

• Account for more than 50% of the dry weight of most cells

Amino Acids

Amino acids are the building blocks of proteins. There are 20 different amino acids, each with a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a unique side chain (R group).

• General structure: $NH_2-CHR-COOH$

• The sequence of amino acids determines protein shape and function

Peptide Bonds and Protein Structure

Proteins are formed by linking amino acids via peptide bonds (dehydration reaction). Long chains of amino acids are called polypeptides.

• Protein shape: Determined by amino acid sequence; crucial for function

• Example: Sickle-cell disease is caused by a single amino acid change in hemoglobin

Nucleic Acids

Overview

Nucleic acids are macromolecules that store and transmit genetic information. The two main types are DNA and RNA.

• DNA (deoxyribonucleic acid): Stores genetic information

• RNA (ribonucleic acid): Involved in protein synthesis; uses uracil instead of thymine

Nucleotides

Nucleic acids are polymers made from nucleotide monomers. Each nucleotide consists of three parts:

• A five-carbon sugar (deoxyribose in DNA, ribose in RNA)

• A phosphate group

• A nitrogenous base (A, T, G, C in DNA; A, U, G, C in RNA)

Nucleotides are linked together to form a sugar-phosphate backbone.

Summary Table: Macromolecules and Their Monomers

Macromolecule	Monomer	Main Function	Example
Carbohydrates	Monosaccharides	Energy storage, structure	Glucose, starch, cellulose
Lipids	Glycerol & Fatty acids	Energy storage, membranes, hormones	Fats, oils, cholesterol
Proteins	Amino acids	Enzymes, structure, transport	Hemoglobin, enzymes
Nucleic acids	Nucleotides	Genetic information	DNA, RNA