Molecular Physiology Overview

Introduction

This study guide provides an overview of the molecular and chemical foundations essential for understanding human physiology. It covers the hierarchy of biological organization, the basic chemical elements in the human body, types of chemical bonds, and the structure and function of major biomolecules.

Hierarchy of Organization

Levels of Biological Organization

• Chemical Level: Atoms and molecules form the basis of all matter. Example: phospholipid molecules.

• Cellular Level: Molecules combine to form cells, the basic unit of life. Example: squamous epithelial cell.

• Tissue Level: Similar cells group together to form tissues. Example: stratified squamous epithelium.

• Organ Level: Different tissues combine to form organs. Example: esophagus.

• Organ System Level: Organs work together in systems. Example: digestive system.

• Organism Level: All organ systems function together in a living human.

Example: The digestive system includes organs such as the esophagus, stomach, and intestines, each composed of tissues and cells built from molecules and atoms.

The Smallest Unit of Matter: Atoms and Elements

Major Elements in the Human Body

• Atoms: The smallest unit of matter, composed of protons, neutrons, and electrons.

• Major elements: Hydrogen (H), Oxygen (O), Carbon (C), Nitrogen (N)

• Other important elements: Sodium (Na), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S), Iron (Fe), Copper (Cu), Iodine (I)

Periodic Table: Elements are organized by atomic number and properties. The human body primarily uses elements from the first few periods and groups.

Chemical Bonds and Molecules

Types of Chemical Bonds

• Ionic Bonds: Formed when electrons are transferred from a metal atom to a non-metal atom, resulting in oppositely charged ions that attract each other. Example: Sodium chloride (NaCl): Na+ (metal) and Cl- (non-metal).

• Covalent Bonds: Formed when two atoms share electrons.

  • Nonpolar covalent bonds: Electrons are shared equally (e.g., H2 molecule).

  • Polar covalent bonds: Electrons are shared unequally, creating partial charges (e.g., water molecule).

• Hydrogen Bonds: Weak attractions between the partially positive hydrogen atom of one polar molecule and the partially negative atom of another (often oxygen or nitrogen).

Importance: Chemical bonds determine the structure and function of molecules in the body, such as proteins, nucleic acids, and cell membranes.

Water, Acids, Bases, and Buffers

Properties and Functions

• Hydrophilic molecules: Dissolve in water (e.g., salts, sugars).

• Hydrophobic molecules: Do not dissolve in water (e.g., lipids).

• Acids: Substances that donate H+ ions, lowering pH.

• Bases: Substances that accept H+ ions, raising pH.

• Buffers: Compounds that minimize changes in pH by absorbing or releasing H+ ions. Example: Bicarbonate buffer system: helps maintain blood pH.

Organic Compounds in the Human Body

Overview

Organic compounds contain carbon bonded to hydrogen and are essential for life. The four major classes are carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates

• Composition: Carbon, hydrogen, and oxygen.

• Functions: Energy source, structural component of cell membranes, genetic material (DNA/RNA).

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

• Disaccharides: Two monosaccharides joined by dehydration synthesis (e.g., sucrose).

• Polysaccharides: Many monosaccharides linked together (e.g., glycogen in muscle and liver cells).

Lipids

• Composition: Hydrophobic molecules made primarily of carbon and hydrogen.

• Fatty acids: Hydrocarbon chains with a carboxyl group (–COOH); can be saturated (no double bonds) or unsaturated (one or more double bonds).

• Triglycerides: Three fatty acids linked to a glycerol backbone; main energy storage form.

• Phospholipids: Glycerol backbone, two fatty acids, and a phosphate group; amphiphilic (hydrophilic head, hydrophobic tail); major component of cell membranes.

• Steroids: Four-ring structure; includes cholesterol, testosterone, and estrogen.

Proteins

• Monomers: Amino acids (20 different types in the body).

• Functions: Structural support, cell communication, muscle contraction, enzymes, hormones, transporters.

• Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Folding into alpha-helices or beta-sheets via hydrogen bonds.

  • Tertiary: Further folding and coiling stabilized by various interactions.

  • Quaternary: Multiple polypeptide chains forming a functional protein.

Nucleic Acids

• Monomers: Nucleotides (composed of a nitrogenous base, pentose sugar, and phosphate group).

• Types:

  • DNA (Deoxyribonucleic acid): Double helix, stores genetic information; bases: adenine (A), guanine (G), cytosine (C), thymine (T).

  • RNA (Ribonucleic acid): Single-stranded, involved in protein synthesis; bases: adenine (A), guanine (G), cytosine (C), uracil (U).

• ATP (Adenosine triphosphate): Nucleotide with three phosphate groups; primary energy carrier in cells.

Table: Comparison of Major Biomolecules

Summary

• The human body is organized hierarchically from atoms to the whole organism.

• Major elements and chemical bonds form the foundation for biological molecules.

• Organic compounds—carbohydrates, lipids, proteins, and nucleic acids—are essential for structure and function in physiology.