Unit 1: Chemistry of Life

This unit introduces foundational chemical principles essential for understanding biological systems. It covers the structure and properties of water, the elements vital for life, and the major classes of biological macromolecules.

1.1 Structure of Water and Hydrogen Bonding

Water is a polar molecule, meaning it has partial positive and negative charges due to the unequal sharing of electrons between hydrogen and oxygen atoms. This polarity allows water molecules to form hydrogen bonds with each other, which are weak attractions between the slightly positive hydrogen atom of one water molecule and the slightly negative oxygen atom of another.

• Polarity: Water's bent shape and electronegative oxygen atom create a dipole moment.

• Hydrogen Bonding: Responsible for water's high cohesion, adhesion, surface tension, and its ability to moderate temperature.

• Biological Importance: Hydrogen bonds are crucial for the structure of DNA and proteins.

• Example: Water's high specific heat helps organisms maintain stable internal temperatures.

1.2 Elements of Life

Living organisms are primarily composed of a small subset of elements. The most abundant elements in biological systems are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), often referred to as CHON.

• Major Elements: C, H, O, N, phosphorus (P), and sulfur (S).

• Trace Elements: Required in smaller amounts (e.g., iron, iodine, zinc).

• Role: These elements form the backbone of biomolecules and are involved in metabolic processes.

• Example: Phosphorus is a key component of nucleic acids and ATP.

1.3 Introduction to Macromolecules

Macromolecules are large, complex molecules essential for life. They are typically formed by the polymerization of smaller subunits called monomers.

• Four Major Classes: Carbohydrates, lipids, proteins, and nucleic acids.

• Polymerization: Most macromolecules (except lipids) are polymers built from monomers via dehydration synthesis reactions.

• Hydrolysis: Polymers are broken down into monomers by hydrolysis reactions.

• Example: Starch is a carbohydrate polymer made of glucose monomers.

1.4 Carbohydrates

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

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

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

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

• Function: Energy storage (starch, glycogen) and structural support (cellulose in plants, chitin in fungi).

1.5 Lipids

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

• Fats (Triglycerides): Composed of glycerol and three fatty acids; used for long-term energy storage.

• Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails.

• Steroids: Lipids with a carbon skeleton of four fused rings (e.g., cholesterol, hormones).

• Function: Energy storage, membrane structure, signaling molecules.

1.6 Nucleic Acids

Nucleic acids store and transmit genetic information. The two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

• Monomers: Nucleotides, each consisting of a sugar, phosphate group, and nitrogenous base.

• DNA: Double-stranded helix; stores genetic information.

• RNA: Single-stranded; involved in protein synthesis and gene regulation.

• Example: ATP (adenosine triphosphate) is a nucleotide that stores cellular energy.

1.7 Proteins

Proteins are polymers of amino acids and perform a vast array of functions in cells, including catalysis, structure, transport, and signaling.

• Amino Acids: Building blocks of proteins; 20 different types in living organisms.

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

• Enzymes: Proteins that catalyze biochemical reactions.

• Example: Hemoglobin transports oxygen in the blood.