Biochemistry: Water, Salts, Acids, Bases, and Organic Molecules in Anatomy & Physiology

Biochemistry in Anatomy & Physiology

Introduction

Biochemistry is the study of the chemical composition and reactions of living matter. Understanding the properties of water, salts, acids, bases, and organic molecules is essential for comprehending physiological processes and maintaining homeostasis in the human body.

Water and Its Biological Importance

Properties and Functions of Water

• High Heat Capacity: Water can absorb and release large amounts of heat with little temperature change, helping to stabilize body temperature.

• High Heat of Vaporization: Evaporation of water requires significant energy, providing an effective cooling mechanism (e.g., sweating).

• Reactivity: Water is involved in hydrolysis and dehydration synthesis reactions, essential for breaking down and forming biological molecules.

• Cushioning: Water protects organs from physical trauma (e.g., cerebrospinal fluid cushions the brain).

• Polar Solvent Properties: Water dissolves and dissociates ionic substances, forming hydration layers around large molecules, making it the body's major transport medium.

Salts

Role and Properties

• Definition: Salts are ionic compounds that dissociate into separate ions in water.

• Electrolytes: All salts are electrolytes because they conduct electrical currents in solution.

• Physiological Importance:

  • Sodium and potassium ions are essential for nerve impulses and muscle contractions.

  • Iron is necessary for hemoglobin in blood.

  • Zinc and copper are important for enzyme activity.

• Homeostasis: Maintaining proper ion balance is vital for physiological homeostasis.

Acids and Bases

Definitions and Properties

• Acids: Proton donors that release hydrogen ions (H+) in solution. The concentration of H+ determines acidity.

• Bases: Proton acceptors that take up H+ or release hydroxide ions (OH-).

• Electrolytes: Both acids and bases dissociate in water to form electrolytes.

• pH Scale: Measures the concentration of H+ ions in a solution.

  • pH is the negative logarithm of H+ concentration: $pH = -\log[H^+]$

  • pH scale ranges from 0 (most acidic) to 14 (most alkaline/basic), with 7 being neutral.

  • Each pH unit represents a tenfold difference in H+ concentration.

• Buffers: Systems that resist abrupt changes in pH by converting strong acids/bases into weak ones. The carbonic acid-bicarbonate system is a major buffer in blood.

Organic Compounds: Synthesis and Hydrolysis

General Characteristics

• Organic molecules contain carbon and are usually large and covalently bonded.

• Major organic compounds include carbohydrates, lipids, proteins, and nucleic acids.

• Polymers: Large molecules made up of repeating subunits called monomers.

• Dehydration Synthesis: Joins monomers by removing a water molecule (removal of H from one monomer and OH from another).

• Hydrolysis: Breaks polymers into monomers by adding water to split covalent bonds.

Carbohydrates

Classification and Functions

• Include sugars and starches; contain C, H, and O in a 1:2:1 ratio.

• Functions: Primary source of energy for cells.

• Classes:

  • Monosaccharides: Single sugar units (e.g., glucose, fructose, galactose).

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

  • Polysaccharides: Long chains of monosaccharides (e.g., starch in plants, glycogen in animals).

• Isomers: Molecules with the same molecular formula but different structures and properties.

Monosaccharides

• Simple sugars containing three to seven carbon atoms.

• General formula: $(CH_2O)_n$ where n = number of carbon atoms.

• Examples: Glucose, fructose, galactose.

Disaccharides

• Formed by dehydration synthesis of two monosaccharides.

• Examples: Sucrose (glucose + fructose), maltose (glucose + glucose), lactose (glucose + galactose).

Polysaccharides

• Polymers of monosaccharides formed by dehydration synthesis.

• Starch: Storage form in plants.

• Glycogen: Storage form in animals (liver for blood glucose maintenance, muscles for activity).

• If glycogen stores are full, excess glucose is converted to fat.

Lipids

Types and Functions

• Contain C, H, O (less O than carbohydrates); sometimes contain phosphorus.

• Main types: Triglycerides, phospholipids, steroids, eicosanoids.

Triglycerides

• Composed of three fatty acids bonded to a glycerol molecule by dehydration synthesis.

• Main functions: Energy storage, insulation, protection.

• Fatty acids can be:

  • Saturated: No double bonds; solid at room temperature (e.g., animal fats).

  • Unsaturated: One or more double bonds; liquid at room temperature (e.g., plant oils, omega-3 fatty acids).

Phospholipids

• Modified triglycerides with two fatty acids and a phosphorus-containing group.

• Have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.

• Main component of cell membranes.

Steroids

• Four interlocking hydrocarbon rings.

• Cholesterol is the most important steroid, used in cell membranes and as a precursor for steroid hormones and bile salts.

Eicosanoids

• Derived from arachidonic acid (a fatty acid) in cell membranes.

• Prostaglandins are the most important eicosanoids, involved in inflammation, blood clotting, and labor contractions.

Proteins

Structure and Function

• Contain C, H, O, N (sometimes S and P).

• Made from 20 types of amino acids, each with an amine group and an acid group.

• Peptide bonds link amino acids to form polypeptides and proteins.

• Structure levels:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helices and beta sheets formed by hydrogen bonding.

  • Tertiary: 3D folding due to side chain interactions.

  • Quaternary: Multiple polypeptide chains forming a functional protein.

• Fibrous proteins: Provide mechanical support and strength (e.g., collagen).

• Globular proteins: Functional proteins (e.g., enzymes, antibodies).

Enzymes

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

• Highly specific for their substrates.

• Names often end in -ase (e.g., lactase, protease).

• Enzyme action involves substrate binding, transition state formation, and product release.

ATP (Adenosine Triphosphate)

Role in Cellular Energy

• ATP is the primary energy carrier in cells.

• Energy is released when ATP is hydrolyzed to ADP and inorganic phosphate:

$ATP \rightarrow ADP + P_i + \text{energy}$

• ATP is regenerated from ADP by cellular respiration.

Summary Table: Major Classes of Biological Molecules

Class	Monomer	Main Functions	Examples
Carbohydrates	Monosaccharides	Energy source, structural support	Glucose, starch, glycogen
Lipids	Glycerol & Fatty acids	Energy storage, insulation, membranes	Triglycerides, phospholipids, steroids
Proteins	Amino acids	Structure, enzymes, transport, defense	Collagen, hemoglobin, enzymes
Nucleic Acids	Nucleotides	Genetic information, protein synthesis	DNA, RNA

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.