Introduction to Biochemistry

Definition and Scope

Biochemistry is the study of the molecules that compose living organisms, including carbohydrates, fats, proteins, and nucleic acids. Understanding biochemistry is essential for grasping cellular structures, basic physiology, nutrition, and health.

Salts & Electrolytes

Importance and Functions

• Salts (e.g., sodium chloride, NaCl) are crucial for fluid balance, nerve impulse transmission, muscle contraction, metabolism, and acid-base balance in the blood.

• Salts dissociate in water to become electrolytes, which are substances that carry an electrical current in solution.

• Major electrolytes include sodium, potassium, calcium, magnesium, chloride, bicarbonate, and phosphate.

• Electrolytes are vital for heart health and all physiological processes that depend on electrical activity.

Free Radicals & Antioxidants

Definitions and Biological Impact

• Free radicals are unstable, highly reactive particles with unpaired electrons. They are produced by normal metabolism, radiation, and certain chemicals.

• Free radicals can damage molecules, contributing to cancer, tissue death, and aging.

• Examples include superoxide anion, hydrogen peroxide, and nitric oxide.

• Antioxidants neutralize free radicals. Dietary antioxidants include selenium, vitamin E, vitamin C, and carotenoids.

Water

Role in the Human Body

• Water is the universal solvent, making up 50–75% of body weight.

• Functions include forming blood plasma, supporting metabolism, lubricating joints, and stabilizing internal temperature.

• Calorie: The amount of heat required to raise the temperature of 1g of water by 1°C.

Mixtures: Solutions, Colloids, and Suspensions

Types and Properties

• Solution: Solute particles (<1 nm) dissolve in a solvent (usually water), do not scatter light, pass through membranes, and do not separate on standing.

• Colloid: Particles (1–100 nm) scatter light, are cloudy, do not pass through membranes, and remain mixed.

• Suspension: Particles (>100 nm) are too large to pass through membranes, appear cloudy/opaque, and separate on standing (e.g., blood cells in plasma).

• Emulsion: Suspension of one liquid in another (e.g., fat in breast milk).

Acids, Bases, and pH

pH Scale and Physiological Importance

• pH measures acidity or alkalinity: 7.0 is neutral, <7 is acidic, >7 is basic.

• Acids release hydrogen ions (H+), bases accept them.

• Blood pH is tightly regulated between 7.35–7.45 for proper physiological function.

Energy and Work

Forms of Energy in Biology

• Energy is the capacity to do work, such as moving muscles or molecules.

• Potential energy: Stored energy (e.g., ATP).

• Kinetic energy: Energy of motion (e.g., muscle movement, blood flow).

• Heat is a byproduct of kinetic energy.

Metabolism

Definition and Types

• Metabolism encompasses all chemical reactions in the body.

• Anabolism: Building molecules.

• Catabolism: Breaking down molecules.

• Examples: Cellular respiration (glucose to ATP), digestion, DNA replication, fat breakdown.

Monomers and Polymers

Macromolecules in Biology

• Macromolecules are large organic molecules, often polymers made of repeating monomers.

• Examples: Proteins (amino acids), nucleic acids (nucleotides), carbohydrates (monosaccharides), lipids (fatty acids/glycerol).

• Polymerization joins monomers; catabolism breaks polymers, anabolism builds them.

Carbon Compounds and Functional Groups

Major Classes of Biomolecules

• Carbohydrates: Sugars and starches for quick energy (e.g., glucose, fructose, lactose, sucrose, starch).

• Lipids: Fats for long-term energy storage and insulation (e.g., saturated/unsaturated fats, cholesterol).

• Proteins: Structural and functional molecules (e.g., enzymes, hormones, antibodies, hair, nails).

• Nucleic acids: Information storage and transfer (e.g., ATP, DNA, RNA).

Carbohydrates

Structure and Function

• Composed of carbon (C), hydrogen (H), and oxygen (O) in a 2:1 H:O ratio.

• General formula: (n = number of carbon atoms, typically 6 for glucose).

• Hydrophilic (water-soluble) molecules.

• Monosaccharides (e.g., glucose) are the most important monomers in the body.

Polysaccharides

• Glycogen: Energy storage in liver, muscle, brain.

• Starch: Plant energy storage, digestible by humans.

• Cellulose: Plant structural molecule, indigestible dietary fiber for humans.

Lipids (Fats, Oils, Waxes)

Structure and Types

• Composed of C, H, O; hydrophobic with a high H:O ratio.

• Provide more calories per gram than carbohydrates (9 Cal/g).

• Five main types: fatty acids, triglycerides, phospholipids, eicosanoids, steroids.

Fatty Acids

• Saturated fatty acids: Single bonds, "solid" fats (e.g., butter).

• Unsaturated fatty acids: One or more double bonds, "liquid" fats (e.g., oils).

• Polyunsaturated: Multiple double bonds.

• Essential fatty acids must be obtained from the diet.

Triglycerides

• Three fatty acids linked to glycerol via dehydration synthesis; broken down by hydrolysis.

• Primary function: energy storage, insulation, shock absorption.

• Oils (liquid at room temperature) are usually plant-derived; fats (solid) are animal-derived.

Eicosanoids & Steroids

• Cholesterol: Parent steroid, structural component of membranes, precursor for hormones (testosterone, estrogen), and vitamin D synthesis.

• Eicosanoids: Short-range hormone-like signals, important in inflammation and blood clotting. Many drugs (e.g., NSAIDs) block eicosanoid synthesis.

Proteins

Structure and Function

• Polymers of amino acids (C, H, O, N).

• Amino acids have a central carbon, amino group (-NH2), carboxyl group (-COOH), and variable R group.

• 20 amino acids differ by their R group, determining their properties.

• Proteins are the most functionally diverse macromolecules, making up about 42% of the body (excluding water).

Protein Structure

• Proteins have complex 3D shapes (conformations) crucial for function.

• Can reversibly change shape (important for muscle contraction, enzyme function, membrane channels).

• Denaturation: Extreme, permanent conformational change (e.g., by heat or pH) that destroys function.

• Protein structure levels: primary (sequence), secondary (folding), tertiary (3D shape), quaternary (multiple chains).

Enzymes

Biological Catalysts

• Enzymes are proteins that act as catalysts, speeding up reactions by lowering activation energy.

• They act on substrates, are reusable, and permit reactions at body temperature.

• Enzyme names often end in -ase (e.g., amylase, lactase).

Enzyme Structure and Action

• Enzyme activity is affected by temperature and pH; optimal conditions are required for function.

• Denaturation can inactivate enzymes.

Nucleotides and Nucleic Acids

ATP and Genetic Material

• ATP (Adenosine Triphosphate): The cell's energy currency, a nucleotide composed of adenine, ribose, and three phosphate groups.

• Nucleotides are monomers for nucleic acids (DNA, RNA).

• DNA is a polymer of four nucleotides (adenine, thymine, cytosine, guanine).

DNA and RNA

• DNA (deoxyribonucleic acid): Double-stranded, contains genetic instructions for protein synthesis.

• Genes are segments of DNA coding for proteins.

• RNA (ribonucleic acid): Reads DNA code and helps synthesize proteins (mRNA, tRNA, rRNA).