Biochemistry Study Guide: Chemical Context of Life & Macromolecules

Introduction to Biochemistry

Chemical Context of Life

Biochemistry explores the chemical principles underlying biological systems. Understanding atoms, molecules, and their interactions is foundational for studying life at the molecular level.

• Elements: Substances that make up matter, such as carbon, hydrogen, nitrogen, and oxygen.

• Atoms: Basic units of elements, consisting of protons, neutrons, and electrons.

• Molecules: Groups of atoms bonded together, forming the chemical basis of biological structures.

• Electronegativity: The tendency of an atom to attract electrons. Higher electronegativity means stronger attraction (e.g., O > N > C > H).

Bond Types: Covalent bonds (sharing electrons), ionic bonds (transfer of electrons), and hydrogen bonds (weak attractions between molecules).

Electronegativity Table:

Element	Electronegativity
Oxygen (O)	3.5
Nitrogen (N)	3.0
Carbon (C)	2.5
Hydrogen (H)	2.1

Water

Properties of Water

Water is essential for life due to its unique chemical and physical properties. Its polarity and hydrogen bonding enable it to support biological processes.

• Universal Solvent: Water dissolves many substances, facilitating biochemical reactions.

• High Heat Capacity: Water absorbs and retains heat, stabilizing temperature in organisms.

• Density: Ice is less dense than liquid water, allowing ice to float and insulate aquatic life.

• Cohesion & Adhesion: Water molecules stick to each other (cohesion) and to other surfaces (adhesion).

• Surface Tension: Water's surface resists external force due to cohesive hydrogen bonds.

Chemical Bonds

Types of Covalent Bonds

Covalent bonds are fundamental to molecular structure in biochemistry. They can be classified as polar or non-polar based on electron sharing.

• Polar Covalent Bonds: Unequal sharing of electrons, resulting in partial charges (e.g., H2O).

• Non-Polar Covalent Bonds: Equal sharing of electrons, no charge separation (e.g., O2).

Hydrogen Bonds: Weak interactions between a hydrogen atom and an electronegative atom (e.g., O or N).

Van der Waals Interactions: Weak attractions due to transient dipoles in molecules.

Macromolecules

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as energy sources and structural components in cells.

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

• Disaccharides: Two monosaccharides joined by glycosidic bonds (e.g., sucrose).

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

• Alpha and Beta Linkages: Different glycosidic bond orientations affect structure and function.

Example: Glucose (C6H12O6) is a common monosaccharide used in cellular respiration.

Lipids

Lipids are hydrophobic molecules that include fats, oils, phospholipids, and steroids. They are important for energy storage, membrane structure, and signaling.

• Fatty Acids: Long hydrocarbon chains with a carboxyl group.

• Triglycerides: Glycerol backbone with three fatty acids, formed by dehydration synthesis.

• Phospholipids: Major component of cell membranes, with hydrophilic heads and hydrophobic tails.

• Steroids: Four fused carbon rings, including cholesterol and hormones.

Cell Membrane Fluidity: Influenced by the saturation of fatty acids and cholesterol content.

Proteins

Proteins are polymers of amino acids, performing diverse functions such as catalysis, structure, transport, and regulation.

• Structure: Amino acids linked by peptide bonds form polypeptides.

• Functions: Enzymes, structural proteins, transport proteins, signaling molecules.

• Levels of Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.

  • Tertiary: 3D folding due to interactions among side chains.

  • Quaternary: Association of multiple polypeptide chains.

• Denaturation: Loss of protein structure due to environmental changes.

Nucleic Acids

Nucleic acids (DNA and RNA) store and transmit genetic information. They are polymers of nucleotides, each consisting of a sugar, phosphate, and nitrogenous base.

• DNA: Double helix, stores genetic information.

• RNA: Single-stranded, involved in protein synthesis.

• Nucleotide Structure: Sugar (ribose or deoxyribose), phosphate group, nitrogenous base (A, T, G, C, U).

• Base Pairing: A-T (DNA), A-U (RNA), G-C.

• Chargaff's Rule: Amounts of A = T and G = C in DNA.

Example: DNA replication and transcription are central to gene expression.

Additional info:

• These notes cover foundational biochemistry topics, including chemical bonds, water, macromolecules (carbohydrates, lipids, proteins, nucleic acids), and their properties and functions.

• Key equations and concepts are included for exam preparation.