Chapter 2: The Chemical Basis of Life – Structured Study Notes

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Basic Chemistry

Elements

Elements are the fundamental substances that make up all matter. There are 92 naturally occurring elements, with six (CHNOPS: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur) comprising 90–99% of living organisms.

Element: A pure substance consisting of only one type of atom.
CHNOPS: Essential elements for life.

Atoms

An atom is the smallest unit of an element, composed of three subatomic particles:

Proton: Mass = 1, Charge = +1 (located in nucleus)
Neutron: Mass = 1, Charge = 0 (located in nucleus)
Electron: Mass ≈ 0, Charge = -1 (orbits nucleus)

Atomic Number: Number of protons (equals number of electrons in a neutral atom)
Atomic Mass: Number of protons + neutrons
Isotopes: Atoms of the same element with different numbers of neutrons
Energy Levels/Shells: Electrons occupy specific energy levels or orbitals

Examples: Hydrogen (1H1), Helium (4He2), Lithium (7Li3), Carbon (12C6)

Bonds

Atoms combine via chemical bonds to form molecules. The main types of bonds are:

Ionic Bonds: Electrons are transferred; strong in solids, weak in liquids. Example: Sodium (Na+) and Chlorine (Cl-) form NaCl (salt). Electrolytes are ions in solution.
Covalent Bonds: Electrons are shared; strongest and most common. Nonpolar (equal sharing, e.g., CH4), Polar (unequal sharing, e.g., H2O).
Hydrogen Bonds: Weak bonds between atoms of polar covalent molecules (e.g., between water molecules).

Chemical Reactions

Overview

Chemical reactions involve the rearrangement of bonds between atoms, requiring proper orientation and energy. Reactants are transformed into products.

Synthesis: A + B → AB (e.g., Na+ + Cl- → NaCl). Anabolism refers to all synthesis reactions in the body. Dehydration/Condensation produces water.
Degradation/Decomposition: AB → A + B (e.g., H2O → H+ + OH-). Catabolism refers to all degradation reactions. Hydrolysis splits water.
Exchange: AB + CD → AD + BC (e.g., NaOH + HCl → H2O + NaCl)
Reversible: Reactions can proceed in both directions (e.g., )
Redox Reactions: Involve electron transfer ("LEO says GER": Lose Electrons = Oxidation, Gain Electrons = Reduction)

Factors Affecting Reaction Rate

Enzymes: Biological catalysts that speed up reactions
Temperature: Higher temperature increases rate
pH: Optimal pH required for maximum rate
Amount of Reactants: More reactants increase rate

Energy

Types of Energy

Energy is the capacity to do work. It exists as:

Potential Energy: Stored energy
Kinetic Energy: Energy of motion

Forms of Energy

Electrical: Movement of ions/electrons (important in nerves and muscles)
Electromagnetic: Energy in waves (gamma, UV, visible, IR, micro, radio)
Chemical: Energy stored in bonds between molecules
Heat: Produced by random movement; exergonic reactions/catabolism generate body heat
Mechanical/Kinetic: Movement

Energy Transfer

Not efficient; some energy lost as heat or light
Activation Energy: Minimum energy required to start a reaction; lowered by enzymes

Endergonic vs. Exergonic Reactions

Type	Bond Formation	Energy	Metabolic Process
Endergonic	Makes bonds	Stores/requires energy	Anabolism
Exergonic	Breaks bonds	Releases energy	Catabolism

Metabolism = Anabolism + Catabolism

Inorganic Molecules

Water

Water is essential for life and has several functions:

Temperature Buffer: Maintains stable internal temperature
Protection: Lubricates and removes toxins
Chemical Reactions: Most reactions occur in or with water
Mixing Medium: Forms solutions, suspensions, colloids
Solvent: Water dissolves solutes to form solutions
Osmolality: Number of particles dissolved in solution (measured in mOsm)

Acids & Bases

Acid: Donates H+; pH 1–6
Base: Accepts H+ (donates OH-); pH 8–14
Neutral: pH 7; equal H+ and OH-
pH Scale: Each unit represents a tenfold change in H+ concentration
Salts: Cation other than H+, anion other than OH-
Buffers: Resist changes in pH by donating or accepting H+

Example:

Oxygen and Carbon Dioxide

Oxygen: Required for aerobic respiration and energy production
Carbon Dioxide: Released during aerobic respiration

Organic Molecules

Organic molecules contain carbon held together by covalent bonds. Four major macromolecules are found in living organisms.

Carbohydrates

Function: Energy, structure, bulk in feces
Monomers: Monosaccharides (single sugars; e.g., glucose, fructose)
Disaccharides: Double sugars (e.g., sucrose)
Polysaccharides: Many sugars (e.g., starch, cellulose, chitin in plants; glycogen in animals)

Lipids

Types: Fats, oils, waxes; nonpolar, insoluble in water
Triglycerides: Glycerol + 3 fatty acids
Saturated: No C=C bonds; found in animals and palm oil
Unsaturated: C=C bonds present; found in plants and fish
Phospholipids: Major component of cell membranes
Cholesterol: Structural and regulatory roles

Function	Example
Vitamins (A, D, E, K)	Regulation
Energy	Triglycerides
Insulation	Fat tissue
Protection	Waxes
Structure	Phospholipids

Proteins

Amino Acids: 20 types; joined by peptide bonds
Structure: Primary (chain), secondary (helix/sheet), tertiary (globular), quaternary (multiple chains, e.g., hemoglobin)
Functions: Contraction (muscle), regulation (enzymes, hormones), energy, protection (antibodies), transport, structure (collagen, keratin)
Denaturation: Loss of function due to change in shape (caused by temperature, pH, chemicals)

Nucleic Acids

Nucleotide: Building block; consists of 5-carbon sugar, phosphate, nitrogenous base
Purines: Double rings (Adenine, Guanine)
Pyrimidines: Single rings (Cytosine, Thymine/Uracil)
DNA: Double helix; hereditary information; A=T, C=G
RNA: Single strand; found in nucleus and cytoplasm; A=U, C=G
ATP: Adenosine triphosphate; energy currency of cells; produced and used rapidly ( ATP/sec/cell at rest)

Example: ATP is used by 75 trillion cells in the body, totaling ATP used per second.