Introduction to Chemistry in Anatomy & Physiology

The Importance of Chemistry in Human Physiology

Understanding the chemical level of organization is essential for grasping how the human body functions. Chemistry is the physical science that studies the properties of matter, which is anything that takes up space and has mass. Matter exists in three states: solids, liquids, and gases.

Principle Elements of the Body

Atoms and Subatomic Particles

• Atom: The smallest unit of matter, composed of subatomic particles.

• Protons (p+): Positively charged particles found in the nucleus.

• Neutrons (n): Electrically neutral particles also found in the nucleus.

• Electrons (e-): Negatively charged particles orbiting the nucleus in electron shells.

Atomic Structure

• Nucleus: Central part of the atom containing protons and neutrons.

• Electron Cloud: Region where electrons orbit the nucleus.

Atomic Number and Atomic Mass

• Atomic Number: Number of protons in the nucleus (also equals the number of electrons in a neutral atom).

• Atomic Mass: Total number of protons and neutrons in the nucleus.

Electron Shells

• Electrons are arranged in shells around the nucleus:

  • 1st shell: Maximum 2 electrons

  • 2nd shell: Maximum 8 electrons

  • 3rd shell: Maximum 8 electrons

Valence Electrons and Chemical Behavior

• Valence Electrons: Electrons in the outermost shell determine an atom’s chemical properties and reactivity.

Elements and Ions

Inert and Reactive Elements

• Inert Elements: Have filled outer electron shells and do not react (e.g., noble gases).

• Reactive Elements: Have unfilled valence shells and tend to gain, lose, or share electrons to achieve stability.

Ions: Cations and Anions

• Cation: Atom that has lost electrons, resulting in a positive charge (e.g., Na+).

• Anion: Atom that has gained electrons, resulting in a negative charge (e.g., Cl-).

Chemical Bonds

Types of Chemical Bonds

• Covalent Bonds: Atoms share electrons.

  • Non-Polar Covalent Bonds: Electrons are shared equally (e.g., O2, H2).

  • Polar Covalent Bonds: Electrons are shared unequally, creating partial charges (e.g., H2O).

• Ionic Bonds: Formed by electrical attraction between cations and anions (e.g., NaCl).

• Hydrogen Bonds: Weak attractions between the positive charge on hydrogen (in a polar molecule) and a negative charge on another atom (e.g., between water molecules).

Water and Its Properties

Importance of Water

• Water is essential for all bodily functions and exists in all three states of matter.

Hydrogen Bonds in Water

• Hydrogen bonds are responsible for water’s unique properties, such as cohesion, surface tension, and its role as a solvent.

Surface Tension

• Water’s surface tension allows small objects to float and acts as a barrier at the water’s surface.

Water as the Universal Solvent

• Solution: A mixture of solute (dissolved substance) and solvent (dissolving agent; water is the universal solvent).

• Solubility: The degree to which a molecule dissolves in water.

• Ionization/Dissociation: Water can break apart chemical bonds, allowing ions to disperse.

Electrolytes and pH

Electrolytes

• Inorganic substances whose ions conduct electrical currents in water, essential for muscle and neuron function.

pH Scale

• The pH scale is logarithmic; a change of 1 unit equals a tenfold change in [H+].

• Normal blood plasma pH: 7.35–7.45.

• Acidosis: pH below 7.35 (can cause CNS depression and coma).

• Alkalosis: pH above 7.45 (can cause uncontrollable muscle contractions).

Macromolecules

Organic and Inorganic Compounds

• Organic Compounds: Contain large amounts of carbon and hydrogen (e.g., sugars, fats, proteins).

• Inorganic Compounds: Generally lack large amounts of carbon and hydrogen (e.g., water, salts, CO2).

Macromolecules and Monomers

• Macromolecules: Large molecules made of repeating subunits (monomers).

• Dehydration Synthesis: Forms polymers by removing water to create bonds.

• Hydrolysis: Breaks polymers into monomers by adding water.

Lipids

Triglycerides

• Composed of one glycerol and three fatty acids.

• Functions: Energy storage, insulation, and protection of organs.

Fatty Acid Structure

• Hydrophilic Head: Carboxyl group, water-attracting.

• Hydrophobic Tail: Hydrocarbon chain, water-repelling.

Saturated vs. Unsaturated Fatty Acids

• Saturated: No double bonds, solid at room temperature.

• Unsaturated: One or more double bonds, liquid at room temperature.

Other Lipids

• Eicosanoids: Signaling molecules (e.g., inflammation, pain).

• Steroids: Involved in hormone synthesis.

• Phospholipids: Main component of cell membranes.

Carbohydrates

Types of Carbohydrates

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

• Disaccharides: Two monosaccharides joined together.

• Polysaccharides: Long chains of monosaccharides (e.g., glycogen).

Glycogen

• Storage form of glucose in the liver and skeletal muscle; broken down via hydrolysis to release glucose for energy.

Nucleic Acids

Structure and Function

• Nucleic Acids: Long chains of nucleotides; DNA stores genetic information, RNA is involved in protein synthesis.

• Nucleotide Structure: Nitrogenous base (purines: A, G; pyrimidines: C, T, U), 5-carbon sugar, phosphate group.

Proteins

Structure and Function

• Proteins are polymers of amino acids and account for ~20% of body weight.

• The structure of a protein determines its function.

Levels of Protein Structure

• Primary: Sequence of amino acids.

• Secondary: Local folding (e.g., alpha helices, beta sheets).

• Tertiary: Overall 3D shape.

• Quaternary: Arrangement of multiple polypeptide chains.

Protein-Ligand Binding

• Specificity: Ability of a protein to bind a particular ligand.

• Affinity: Strength of the binding between protein and ligand.

• Saturation: Fraction of binding sites occupied by ligand.

• Competition: Ligands compete for binding; antagonists inhibit binding.

Law of Mass Action

• In a chemical reaction, if the concentration of reactants or products changes, the reaction shifts to restore equilibrium.

Protein Activation and Modulation

• Some proteins require activation (e.g., by cofactors or proteolytic cleavage).

• Protein function can be modulated by chemical (allosteric modulators) or physical factors (pH, temperature).

• Up-regulation: Increases protein synthesis.

• Down-regulation: Decreases protein synthesis.

Allosteric Modulation

• Allosteric modulators bind to regulatory sites, altering protein activity.

• Activators increase activity; inhibitors decrease activity.

Physical Modulators

• Extreme temperature, pH, or salt concentration can denature proteins, causing loss of function.

Table: Comparison of Macromolecules

Example: Molecular Structure and Function

Chemical compounds such as propane (fuel), acetic acid (vinegar), and acetylsalicylic acid (aspirin) illustrate the diversity of molecular structures and their roles in daily life and medicine.