Basic Chemistry for Anatomy & Physiology: Atoms, Ions, Bonds, and Biomolecules

Introduction to Chemistry in Anatomy & Physiology

Understanding basic chemistry is essential for studying anatomy and physiology, as it underpins the structure and function of the human body and the distinction between healthy and diseased states.

Structure of an Atom

Atomic Structure

• All matter, including the human body, is composed of particles called atoms.

• Atoms are made up of three subatomic particles:

  • Protons: Positively charged particles located in the nucleus.

  • Neutrons: Neutral particles also found in the nucleus.

  • Electrons: Negatively charged particles orbiting the nucleus.

• Atoms are electrically neutral when the number of protons equals the number of electrons.

• Isotopes are atoms of the same element with different numbers of neutrons.

Ions

Formation and Importance of Ions

• An ion is formed when an atom gains or loses electrons, becoming electrically charged.

• Cation: Atom loses electrons (positively charged ion). Anion: Atom gains electrons (negatively charged ion).

• Common physiological ions (electrolytes):

  • Calcium: Ca2+

  • Sodium: Na+

  • Potassium: K+

  • Hydrogen: H+

  • Chloride: Cl-

Chemical Bonds

Types of Chemical Bonds

• Bonds hold atoms together to form molecules.

• Ionic Bonds:

  • Formed by the transfer of electrons from one atom to another.

  • Result in the formation of salts (e.g., NaCl).

  • Salts consist of cations and anions held together by electrostatic attraction.

• Covalent Bonds:

  • Formed by the sharing of electrons between atoms.

  • Can be single, double, or triple bonds depending on the number of shared electron pairs.

  • Found in organic molecules (e.g., carbohydrates, proteins, lipids, nucleic acids).

Water (Inorganic)

Properties and Biological Importance

• Most abundant substance in cells.

• Composed of hydrogen and oxygen (H2O).

• Polar molecule: Unequal sharing of electrons leads to a slight charge difference.

• Universal solvent: Dissolves many substances, facilitating chemical reactions.

• Transports chemicals (e.g., O2, CO2, nutrients).

• Maintains body temperature due to high heat capacity.

Acids and Bases

Definitions and Biological Roles

• Acids: Substances that dissociate in water to release H+ ions.

  • Example: HCl → H+ + Cl-

• Bases: Substances that accept H+ ions or release OH- ions.

  • Example: NaOH → Na+ + OH-

• pH Scale: Measures the concentration of H+ ions in a solution.

  • Acidic: pH < 7

  • Neutral: pH = 7

  • Basic/Alkaline: pH > 7

  • Normal blood pH: 7.35 – 7.45

• Buffer systems help maintain pH balance in the body.

Important Organic Substances

1. Carbohydrates

• Composed of carbon, hydrogen, and oxygen (C, H, O).

• General formula: (CH2O)n

• Functions:

  • Primary source of energy for cells (e.g., glucose).

  • Structural components (e.g., DNA, RNA backbone).

• Classification:

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

  • Disaccharides: Two monosaccharides covalently bonded (e.g., sucrose, lactose).

  • Polysaccharides: Many monosaccharides bonded together (e.g., glycogen in animals, starch in plants).

2. Lipids

• Composed mainly of C, H, O (less O than carbohydrates).

• Types include fats, oils, waxes, and steroids.

• Functions:

  • Energy storage.

  • Insulation and protection (padding).

  • Component of cell membranes.

• Types of Lipids:

  • Triglycerides: Most common lipid in body and diet; composed of glycerol and three fatty acids.

  • Phospholipids: Major component of cell membranes; contain a phosphate "head" (polar, water-soluble) and two fatty acid "tails" (non-polar, water-insoluble).

  • Cholesterol: Found in cell membranes and used to synthesize steroids.

  • Steroids: Derived from cholesterol (e.g., bile salts, vitamin D, hormones like testosterone and estrogen).

3. Proteins

• Composed of C, H, O, N (sometimes S).

• Functions:

  • Structural materials (e.g., collagen).

  • Enzymes, hormones, transporters.

  • Source of energy (especially when carbohydrates and lipids are in low supply).

• Structure:

  • Made of amino acids (20 different types).

  • Amino acids are linked by peptide bonds to form polypeptides.

  • Proteins are polypeptides folded into a specific three-dimensional shape.

4. Nucleic Acids

• Composed of C, H, O, N, P.

• Types:

  • DNA (deoxyribonucleic acid): Double-stranded helix; stores genetic information.

  • RNA (ribonucleic acid): Single-stranded; involved in protein synthesis.

• Nucleotides are the building blocks, each consisting of a phosphate group, a sugar (deoxyribose or ribose), and a nitrogenous base (A, T, C, G for DNA; A, U, C, G for RNA).

• Functions:

  • DNA: Cellular reproduction, genetic information storage.

  • RNA: Protein synthesis.

5. Adenosine Triphosphate (ATP)

• Modified RNA nucleotide; primary energy carrier in cells.

• Structure: Adenosine (adenine + ribose) + 3 phosphate groups.

• Energy is stored in covalent bonds between phosphate groups.

• Hydrolysis of ATP releases energy for cellular activities: $ATP \rightarrow ADP + P_i + \text{energy}$

Summary Table: Key Inorganic and Organic Substances

Substance	Type	Main Function	Example
Water	Inorganic	Solvent, temperature regulation	H2O
Carbohydrates	Organic	Energy source, structure	Glucose, glycogen
Lipids	Organic	Energy storage, membranes	Triglycerides, phospholipids
Proteins	Organic	Structure, enzymes, transport	Collagen, hemoglobin
Nucleic Acids	Organic	Genetic information, protein synthesis	DNA, RNA
ATP	Organic	Energy transfer	ATP molecule