Chemistry and the Human Body

What is Chemistry?

Chemistry is the physical science that studies the properties of matter, which is anything that takes up space and has mass. Understanding chemistry is essential for grasping the chemical level of organization in the human body.

• Matter exists in three states: solids, liquids, and gases.

• All bodily functions depend on chemical interactions and reactions.

Principle Elements of the Body

The human body is composed of several key elements, including carbon, hydrogen, oxygen, and nitrogen, which are fundamental to biological molecules and processes.

The Atom

Structure of the Atom

An atom is the smallest unit of matter and is 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.

The nucleus contains protons and neutrons, while electrons are found in the electron cloud surrounding the nucleus.

Atomic Number & 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 of 2 electrons.

• 2nd and 3rd shells: Maximum of 8 electrons each.

The chemical behavior of an atom depends on the number of valence electrons in its outermost shell.

Atoms, Ions, and Chemical Bonds

Inert and Reactive Elements

• Inert Elements: Have filled outer electron shells and do not react with other elements (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

• Cations: Atoms that have lost electrons, resulting in a positive charge (e.g., Na+).

• Anions: Atoms that have gained electrons, resulting in a negative charge (e.g., Cl-).

Chemical Bonds

• Covalent Bonds: Atoms share electrons. Can be non-polar (equal sharing) or polar (unequal sharing).

• Ionic Bonds: Formed by the electrical attraction between cations and anions.

• Hydrogen Bonds: Weak interactions between the positive charge on hydrogen (in a polar molecule) and a negative charge on another atom.

Water and Its Properties

Importance of Water

Water is essential for life and is involved in all bodily functions. It is unique in that it exists in all three states of matter at various temperatures.

Hydrogen Bonds in Water

• Hydrogen bonds are responsible for water's high surface tension and its ability to act as a universal solvent.

• These bonds are constantly forming and breaking in liquid water, are locked in place in ice, and are mostly broken in vapor.

Water as a Universal Solvent

• Solution: A mixture of a solute (dissolved substance) and a solvent (dissolving agent, usually water).

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

• Hydrophilic: Molecules that dissolve readily in water.

• Ionization/Dissociation: Water can disrupt chemical bonds, breaking apart molecules into ions.

Electrolytes

• 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 represents a tenfold change in hydrogen ion concentration.

• Normal blood plasma pH is 7.35–7.45.

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

• Alkalosis: pH above 7.45, can cause sustained muscle contractions.

Macromolecules

Organic and Inorganic Compounds

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

• Inorganic Compounds: Generally do not contain large amounts of carbon and hydrogen (e.g., water, salts, carbon dioxide).

Macromolecules and Monomers

• Macromolecules: Large molecules made of repeating subunits called monomers.

• Dehydration Synthesis: Chemical reaction that forms polymers by joining monomers and releasing water.

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

Lipids

• Triglycerides: Composed of glycerol and three fatty acids; main energy storage form in adipose tissue.

• Fatty Acids: Have hydrophilic heads (carboxyl group) and hydrophobic tails (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: Lipid signaling molecules (e.g., involved in inflammation).

• Steroids: Lipids involved in hormone synthesis.

• Phospholipids: Main component of cell membranes.

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, mainly in liver and skeletal muscle.

Nucleic Acids

• 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

• Proteins: Polymers of amino acids; account for ~20% of body weight and have diverse functions.

• Structure: Primary (amino acid sequence), secondary (alpha helices and beta sheets), tertiary (3D folding), quaternary (multiple polypeptides).

• Peptide Bonds: Link amino acids together.

Protein-Ligand Interactions

Specificity, Affinity, and Saturation

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

• Affinity: Degree of attraction between a protein and its ligand.

• Saturation: Fraction of protein binding sites occupied by ligand; maximum when all sites are occupied.

Competition and Modulation

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

• Law of Mass Action: If the concentration of protein, ligand, or complex changes, the reaction shifts to restore equilibrium.

• Protein Activation: Some proteins require cofactors or proteolytic cleavage to become active.

• Protein Modulation: Modulators (chemical or physical) can alter protein binding or activity.

• Allosteric Modulation: Modulators bind at regulatory sites, affecting protein activity (activators increase, inhibitors decrease binding).

• Physical Modulators: Temperature, pH, and salt concentration can denature proteins, affecting their function.

• Up-Regulation: Increases protein synthesis (e.g., insulin production when blood sugar rises).

• Down-Regulation: Decreases protein synthesis (e.g., removal of insulin receptor when blood sugar normalizes).

Additional info: The image above illustrates the molecular structures of common substances (propane, acetic acid, and aspirin), reinforcing the concept that all matter, including biological molecules, is composed of atoms arranged in specific ways. This is directly relevant to the study of chemistry in anatomy and physiology, as understanding molecular structure is foundational to understanding biological function.