Chapter 2: Chemical Basis of Life

2.1 The Importance of Chemistry in Anatomy and Physiology

Chemistry is fundamental to understanding the structure and function of the human body. All anatomical structures and physiological processes are based on chemical composition and reactions.

• Biochemistry is the study of the chemical processes within living organisms.

• Body components such as carbohydrates, proteins, lipids, nucleic acids, salts, and water are all chemicals.

• Physiological processes (e.g., digestion, muscle contraction) depend on chemical reactions.

• Understanding chemistry aids in diagnosing and treating diseases.

2.2 Fundamentals of Chemistry

Structure of Matter

Matter is anything that occupies space and has mass. It exists as solids, liquids, or gases and is composed of elements.

• Elements: Simplest types of matter with specific chemical properties. There are 98 naturally occurring elements.

• Atoms: Smallest particles of an element that retain its properties.

Types of Elements in the Human Body

• Bulk elements: Required in large amounts (e.g., C, O, H, N, P, S). These make up 95% of body weight.

• Trace elements: Needed in small amounts (e.g., Fe, I). Often components of enzymes.

• Ultratrace elements: Needed in minute amounts (e.g., arsenic for metabolism).

Atomic Structure

• Atoms are composed of subatomic particles:

  • Proton: Large, positive charge

  • Neutron: Large, no charge

  • Electron: Small, negative charge

• Nucleus: Central part of atom, contains protons and neutrons

• Electrons move around the nucleus in energy shells

Atomic Number and Mass Number

• Atomic number: Number of protons in the nucleus (unique for each element)

• Mass number: Number of protons plus neutrons

• Atoms are electrically neutral when protons = electrons

Isotopes

• Isotopes: Atoms of the same element with different numbers of neutrons (different mass numbers)

• Radioactive isotopes: Unstable, emit radiation; used in medical imaging and treatment (e.g., Iodine-131 for thyroid, Cobalt-60 for cancer)

Ionizing Radiation

• High-energy radiation (alpha, beta, gamma) can remove electrons from atoms, forming ions

• Sources: X-rays, radioactive elements, nuclear reactions

• Can damage tissues and interfere with normal growth

2.3 Bonding of Atoms

Atoms bond to achieve stable electron configurations, usually by filling their outermost energy shells.

• Ionic bonds: Formed when electrons are transferred from one atom to another, creating oppositely charged ions (e.g., Na+ and Cl- form NaCl)

• Covalent bonds: Formed when atoms share electrons (e.g., H2, O2, H2O)

• Polar covalent bonds: Electrons are shared unequally, resulting in molecules with partial charges (e.g., water)

• Hydrogen bonds: Weak attractions between the slightly positive hydrogen of one molecule and the slightly negative atom of another (important in water, proteins, DNA)

Types of Chemical Reactions

• Synthesis: Two or more substances combine to form a more complex substance ()

• Decomposition: A complex substance breaks down into simpler substances ()

• Exchange: Parts of two molecules trade places ()

• Reversible: Products can revert to reactants ()

2.4 Electrolytes, Acids, Bases, and Salts

• Electrolytes: Substances that release ions in water, conducting electricity (e.g., NaCl)

• Acids: Release hydrogen ions (H+) in water (e.g., HCl)

• Bases: Release ions that combine with H+ (e.g., NaOH releases OH-)

• Salts: Formed by the reaction of an acid and a base (e.g., NaCl)

pH Scale

• Measures hydrogen ion concentration in solution

• Scale ranges from 0 (most acidic) to 14 (most basic); 7 is neutral

• Each unit represents a tenfold difference in H+ concentration

• Normal blood pH: 7.35–7.45

• Acidosis: Blood pH below 7.35; can cause disorientation, fatigue

• Alkalosis: Blood pH above 7.45; can cause dizziness, nervousness

• Buffers: Chemical systems that resist pH changes (e.g., bicarbonate buffer system)

2.5 Chemical Constituents of Cells

Organic vs. Inorganic Molecules

• Organic molecules: Contain carbon and hydrogen; include carbohydrates, lipids, proteins, nucleic acids

• Inorganic molecules: Usually do not contain both carbon and hydrogen; include water, oxygen, carbon dioxide, salts

Inorganic Substances

• Water: Most abundant compound in the body; solvent, transport medium, temperature regulator

• Oxygen: Used in cellular respiration to release energy

• Carbon dioxide: Waste product of metabolism, exhaled from the body

• Inorganic salts: Provide essential ions (Na+, Cl-, K+, Ca2+); important for nerve function, muscle contraction, water balance

Organic Substances

• Carbohydrates: Main energy source; composed of C, H, O (ratio ~2:1 H:O)

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

  • Disaccharides: Double sugars (e.g., sucrose, lactose)

  • Polysaccharides: Complex carbohydrates (e.g., starch, glycogen, cellulose)

• Lipids: Energy storage, cell membrane structure; include fats (triglycerides), phospholipids, steroids

  • Triglycerides: 1 glycerol + 3 fatty acids; saturated (solid, animal origin) or unsaturated (liquid, plant origin)

  • Phospholipids: 1 glycerol + 2 fatty acids + 1 phosphate; major component of cell membranes

  • Steroids: Four connected carbon rings; cholesterol, hormones

• Proteins: Structural materials, enzymes, hormones, antibodies; made of amino acids joined by peptide bonds

  • Primary structure: Amino acid sequence

  • Secondary structure: Pleated or coiled by hydrogen bonding

  • Tertiary structure: Further folding into 3D shape

  • Quaternary structure: Multiple polypeptide chains joined

• Nucleic acids: Store genetic information (DNA) or aid in protein synthesis (RNA); made of nucleotides (sugar, phosphate, base)

  • DNA: Double helix, deoxyribose sugar, stores genetic code

  • RNA: Single strand, ribose sugar, involved in protein synthesis

2.6 Applications in Medicine and Technology

• Radioactive isotopes: Used in diagnosis (e.g., PET scans, thyroid imaging) and treatment (e.g., cancer therapy)

• CT Scanning: X-ray technique for 3D imaging of internal structures

• PET Imaging: Uses positron-emitting isotopes to study biochemical activity

Additional info: This summary includes expanded explanations and context for clarity and completeness, as expected in a mini-textbook study guide.