Structure and Function of Basic Macromolecules in Biological Systems

Biological Macromolecules

Introduction to Macromolecules

Living organisms are composed of carbon and other elements bonded together to form organic macromolecules. These macromolecules are essential for structure, function, and regulation of the body’s tissues and organs. The four major classes of biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids.

• Macromolecules are large polymers made from smaller subunits called monomers.

• Monomers are joined by dehydration synthesis (removal of water) and broken down by hydrolysis (addition of water).

• Each class of macromolecule has a unique structure and function in biological systems.

Carbohydrates

Structure and Types

Carbohydrates, also known as sugars or starches, are found in all living organisms. They serve as a primary energy source and as structural components.

• Monosaccharides: Simple sugars with the general formula (CH2O)n. Example: Glucose (C6H12O6).

• Disaccharides: Two monosaccharides joined by dehydration synthesis. Example: Sucrose (glucose + fructose).

• Polysaccharides: Long chains of monosaccharides. Examples: Starch (plants), glycogen (animals), cellulose (plant cell walls).

Functions

• Energy storage (starch in plants, glycogen in animals).

• Structural support (cellulose in plants, chitin in fungi and arthropods).

Example

Glycogen is stored in the liver and muscles of animals and is broken down to glucose when energy is needed.

Lipids

Structure and Types

Lipids are hydrophobic molecules that include fats, oils, waxes, phospholipids, and steroids. They are not polymers but are grouped together due to their insolubility in water.

• Fats and oils: Composed of glycerol and three fatty acids (triglycerides).

• Phospholipids: Glycerol, two fatty acids, and a phosphate group; major component of cell membranes.

• Waxes: Long-chain fatty acids bonded to long-chain alcohols.

• Steroids: Four fused carbon rings; include cholesterol and hormones.

Functions

• Energy storage (fats and oils).

• Membrane structure (phospholipids).

• Insulation and protection (fats, waxes).

• Hormonal signaling (steroids).

Example

Phospholipids form the bilayer of cell membranes, creating a barrier between the cell and its environment.

Proteins

Structure and Types

Proteins are polymers of amino acids linked by peptide bonds. They have diverse structures and functions.

• Amino acids: 20 different types, each with a central carbon, amino group, carboxyl group, hydrogen atom, and variable R group.

• Peptide bond: Formed by dehydration synthesis between amino acids.

• Levels of structure: Primary (sequence), secondary (alpha helices, beta sheets), tertiary (3D folding), quaternary (multiple polypeptides).

Functions

• Enzymatic catalysis (enzymes).

• Structural support (collagen, keratin).

• Transport (hemoglobin).

• Defense (antibodies).

• Movement (actin, myosin).

• Regulation (hormones).

Example

Enzymes are proteins that speed up chemical reactions by lowering activation energy. For example, pepsin is an enzyme that digests proteins in the stomach.

Nucleic Acids

Structure and Types

Nucleic acids are polymers of nucleotides, which consist of a sugar, phosphate group, and nitrogenous base. The two main types are DNA and RNA.

• DNA (deoxyribonucleic acid): Double-stranded helix; stores genetic information.

• RNA (ribonucleic acid): Single-stranded; involved in protein synthesis and gene regulation.

Functions

• Storage and transmission of genetic information (DNA).

• Protein synthesis (mRNA, tRNA, rRNA).

• Gene regulation (various types of RNA).

Example

Messenger RNA (mRNA) carries genetic information from DNA to ribosomes, where proteins are synthesized.

Summary Table: Major Macromolecules

Macromolecule	Monomer	Main Functions	Examples
Carbohydrates	Monosaccharides	Energy storage, structure	Glucose, starch, cellulose
Lipids	Glycerol & fatty acids	Energy storage, membranes, hormones	Fats, oils, phospholipids, steroids
Proteins	Amino acids	Catalysis, structure, transport, defense	Enzymes, hemoglobin, antibodies
Nucleic Acids	Nucleotides	Genetic information, protein synthesis	DNA, RNA

Key Equations

• Dehydration Synthesis: Monomer + Monomer → Polymer + H2O

• Hydrolysis: Polymer + H2O → Monomer + Monomer

$\text{Monomer}_1 + \text{Monomer}_2 \xrightarrow{\text{Dehydration}} \text{Polymer} + H_2O$

$\text{Polymer} + H_2O \xrightarrow{\text{Hydrolysis}} \text{Monomer}_1 + \text{Monomer}_2$

Additional info:

• Errors in the sequence of nucleotides in nucleic acids are called mutations and can affect protein structure and function.

• Nucleic acids are present in all foods containing cells, though in small amounts.