Chapter 2: Basic Chemistry for Anatomy & Physiology

Introduction to Basic Chemistry in Anatomy & Physiology

This chapter provides foundational chemical concepts essential for understanding the structure and function of the human body. It covers elements, atoms, molecules, chemical bonds, reactions, and the biological importance of water, salts, acids, bases, and macromolecules.

Chemical Elements and Atoms

Chemical Elements

• Chemical element: A pure substance that cannot be broken down into simpler substances by ordinary chemical means.

• The four elements that form the bulk of body matter are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).

• These elements make up about 96% of the human body’s mass.

Atoms and Subatomic Particles

• Atom: The smallest unit of an element that retains the properties of that element.

• Subatomic particles:

  • Protons: Positive charge (+1), mass ≈ 1 atomic mass unit (amu), located in the nucleus.

  • Neutrons: No charge (0), mass ≈ 1 amu, located in the nucleus.

  • Electrons: Negative charge (–1), mass ≈ 1/1836 amu (very small), located in electron shells around the nucleus.

Atomic Structure and Isotopes

• Atomic number: Number of protons in the nucleus of an atom.

• Atomic mass: Total number of protons and neutrons in an atom’s nucleus.

• Atomic weight: Average mass of all isotopes of an element as found in nature.

• Isotope: Atoms of the same element with different numbers of neutrons.

• Radioisotope: An unstable isotope that emits radiation as it decays to a more stable form.

Molecules, Compounds, and Mixtures

• Molecule: Two or more atoms chemically bonded together (e.g., O2).

• Compound: A molecule containing atoms of two or more different elements (e.g., H2O).

• Mixture: A physical combination of two or more substances where each retains its own properties (e.g., air, salt water).

Comparison of Solutions, Colloids, and Suspensions

Type	Particle Size	Appearance	Stability	Example
Solution	Small (ions, molecules)	Clear	Stable, does not settle	Salt water
Colloid	Intermediate	Cloudy	Stable, does not settle	Milk
Suspension	Large	Cloudy	Unstable, particles settle	Blood cells in plasma

Chemical Bonding and the Octet Rule

• Electrons in the outermost shell (valence shell) are involved in chemical bonding.

• Octet rule: Atoms tend to gain, lose, or share electrons to achieve eight electrons in their valence shell, achieving stability.

Types of Chemical Bonds

• Ionic bonds: Formed when electrons are transferred from one atom to another, creating charged ions (e.g., NaCl).

• Covalent bonds: Formed when atoms share electron pairs (e.g., H2O).

• Hydrogen bonds: Weak attractions between a hydrogen atom (already covalently bonded to another atom) and an electronegative atom (e.g., between water molecules).

Polar vs. Nonpolar Compounds

• Nonpolar compounds: Electrons are shared equally; no charge separation (e.g., O2).

• Polar compounds: Electrons are shared unequally, resulting in partial charges (e.g., H2O).

Chemical Reactions

Types of Chemical Reactions

• Synthesis (Anabolic) reactions: Two or more substances combine to form a more complex substance. General form: $A + B \rightarrow AB$

• Decomposition (Catabolic) reactions: A complex substance breaks down into simpler substances. General form: $AB \rightarrow A + B$

• Exchange reactions: Involves both synthesis and decomposition; parts of molecules are exchanged. General form: $AB + CD \rightarrow AD + CB$

• Oxidation-reduction (redox) reactions: Involve the transfer of electrons between atoms or molecules. Oxidation is the loss of electrons; reduction is the gain of electrons. These reactions are vital for cellular respiration and energy production.

Irreversibility of Chemical Reactions in the Body

• Many reactions in the body are irreversible due to the removal of products, energy changes, or physiological needs.

Factors Affecting Reaction Rates

• Temperature (higher temperature increases rate)

• Concentration of reactants (higher concentration increases rate)

• Particle size (smaller particles react faster)

• Catalysts (e.g., enzymes speed up reactions)

Water, Salts, Acids, and Bases

Importance of Water and Salts

• Water: Most abundant inorganic compound in the body; excellent solvent, involved in temperature regulation, and provides cushioning.

• Salts: Ionic compounds that dissociate in water to form electrolytes, essential for nerve impulse transmission and muscle contraction.

Acids, Bases, and pH

• Acid: Substance that releases hydrogen ions (H+) in solution; proton donor.

• Base: Substance that accepts hydrogen ions or releases hydroxide ions (OH–); proton acceptor.

• pH: A measure of hydrogen ion concentration; scale ranges from 0 (most acidic) to 14 (most basic), with 7 being neutral. pH formula: $\text{pH} = -\log_{10}[\text{H}^+]$

Organic Molecules and Macromolecules

Dehydration Synthesis and Hydrolysis

• Dehydration synthesis: Chemical reaction that joins monomers to form polymers by removing a water molecule.

• Hydrolysis: Chemical reaction that breaks polymers into monomers by adding a water molecule.

Carbohydrates, Lipids, and Proteins

• Carbohydrates:

  • Monomers: Monosaccharides (e.g., glucose)

  • Polymers: Polysaccharides (e.g., glycogen, starch)

  • Function: Main source of energy for cells

• Lipids:

  • Monomers: Glycerol and fatty acids

  • Polymers: Triglycerides, phospholipids, steroids

  • Function: Energy storage, cell membrane structure, hormones

• Proteins:

  • Monomers: Amino acids

  • Polymers: Polypeptides, proteins

  • Function: Enzymes, structural support, transport, signaling

Protein Structure and Enzyme Action

Levels of Protein Structure

• Primary structure: Sequence of amino acids in a polypeptide chain.

• Secondary structure: Local folding into alpha-helices or beta-pleated sheets, stabilized by hydrogen bonds.

• Tertiary structure: Three-dimensional folding due to interactions among R groups.

• Quaternary structure: Association of two or more polypeptide chains to form a functional protein.

Enzyme Action

• Enzymes: Biological catalysts that speed up chemical reactions by lowering activation energy.

• Enzymes are specific for their substrates and are not consumed in the reaction.

• Enzyme action can be summarized as: $\text{E} + \text{S} \rightarrow \text{ES} \rightarrow \text{E} + \text{P}$ where E = enzyme, S = substrate, ES = enzyme-substrate complex, P = product.

Nucleic Acids: DNA and RNA

• DNA (Deoxyribonucleic acid): Double-stranded, stores genetic information, uses deoxyribose sugar, bases are adenine, thymine, cytosine, guanine.

• RNA (Ribonucleic acid): Single-stranded, involved in protein synthesis, uses ribose sugar, bases are adenine, uracil, cytosine, guanine.

• Comparison: DNA is the genetic blueprint; RNA translates the blueprint into proteins.