Chemistry and Matter in Human Physiology

Introduction to Chemistry

Chemistry forms the basis for understanding the structure and function of the human body at the molecular level. Matter, which is anything that takes up space and has mass, exists in three states: solids, liquids, and gases. The properties and interactions of matter are fundamental to physiological processes.

• Chemistry: The physical science that studies the properties of matter.

• Matter: Defined as anything that takes up space and has mass.

• States of Matter: Solids, liquids, and gases.

Principle Elements and Atomic Structure

The Atom

Atoms are the smallest units of matter and are composed of subatomic particles: protons, neutrons, and electrons. The arrangement and number of these particles determine the chemical properties of each element.

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

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

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

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

Electron Shells and Valence Electrons

Electrons occupy specific shells around the nucleus. The chemical behavior of an atom is largely determined by the number of valence electrons in its outermost shell.

• 1st shell: Maximum of 2 electrons

• 2nd shell: Maximum of 8 electrons

• 3rd shell: Maximum of 8 electrons

• Valence Electrons: Electrons in the outermost shell, crucial for chemical bonding.

Chemical Bonds and Molecular Interactions

Types of Chemical Bonds

Atoms achieve stability by gaining, losing, or sharing electrons, forming chemical bonds. The main types of bonds are:

• Non-Polar Covalent Bonds: Electrons are shared equally; no charge separation (e.g., O2, H2, CO2).

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

• Ionic Bonds: Formed by electrical attraction between cations (positive ions) and anions (negative ions).

• Hydrogen Bonds: Weak interactions between hydrogen atoms of one polar molecule and negative atoms of another.

Inert vs. Reactive Elements

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

• Reactive Elements: Have unfilled valence shells and readily form bonds.

Water and Its Biological Importance

Properties of Water

Water is essential for life and exists in all three states of matter. Its polar nature allows it to form hydrogen bonds, which are critical for many physiological functions.

• Surface Tension: Caused by hydrogen bonds, allows small objects to float.

• Universal Solvent: Water dissolves many substances, facilitating biochemical reactions.

• Ionization/Dissociation: Water can break apart molecules into ions.

Electrolytes and pH Balance

Electrolytes

Electrolytes are inorganic substances whose ions conduct electrical currents in water, essential for muscle and neuron function.

pH Scale and Fluctuations

The pH scale measures hydrogen ion concentration. Normal blood plasma pH is 7.35–7.45. Deviations can cause acidosis (below 7.35) or alkalosis (above 7.45), affecting cellular function.

• Acidosis: CNS depression, risk of coma.

• Alkalosis: Uncontrollable muscle contractions.

pH Equation:

Macromolecules: Structure and Function

Organic vs. 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).

Macromolecules and Their Building Blocks

Macromolecules are large molecules made of repeating subunits called monomers. They are formed by dehydration synthesis and broken down by hydrolysis.

• Dehydration Synthesis: Formation of polymers by removing water.

• Hydrolysis: Breakdown of polymers into monomers by adding water.

Lipids

Lipids are diverse molecules with roles in energy storage, cell signaling, and membrane structure.

• Triglycerides: Glycerol + 3 fatty acids; energy storage and insulation.

• Fatty Acids: Hydrophilic head (carboxyl group) and hydrophobic tail (hydrocarbon chain).

• Saturated Fatty Acids: No double bonds; solid at room temperature.

• Unsaturated Fatty Acids: One or more double bonds; liquid at room temperature.

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

• Steroids: Hormone synthesis.

• Phospholipids: Main component of cell membranes.

Carbohydrates

Carbohydrates are classified as monosaccharides, disaccharides, and polysaccharides. Glycogen is a polysaccharide stored in the liver and muscles for energy.

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

• Disaccharides: Two monosaccharides linked (e.g., sucrose).

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

Nucleic Acids

Nucleic acids (DNA and RNA) are polymers of nucleotides, responsible for genetic information and protein synthesis.

• Nucleotides: Composed of a nitrogenous base (purines: A, G; pyrimidines: C, T, U), a 5-carbon sugar, and a phosphate group.

• DNA: Stores genetic information.

• RNA: Involved in protein synthesis and ribosome structure.

Proteins

Proteins are dynamic macromolecules made of amino acids. Their structure determines their function, and they play diverse roles in physiology.

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Alpha helices and beta sheets.

• Tertiary Structure: Three-dimensional folding.

• Quaternary Structure: Multiple polypeptide chains.

Protein-Ligand Interactions

Binding Properties

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

• Affinity: Strength of binding between protein and ligand.

• Saturation: Fraction of binding sites occupied.

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

• Law of Mass Action: Reaction shifts to restore equilibrium if concentrations change.

Protein Activation and Modulation

• Activation: Some proteins require cofactors or proteolytic cleavage.

• Modulation: Chemical (allosteric modulators) or physical (pH, temperature) factors alter protein function.

• Up-Regulation: Increased protein synthesis (e.g., insulin production).

• Down-Regulation: Decreased protein synthesis (e.g., removal of insulin receptor).

Summary Table: Types of Macromolecules