Biological Macromolecules and Water: Structure, Function, and Importance in Anatomy & Physiology

Biological Macromolecules and Water

Learning Objectives

• Compare and contrast organic and inorganic molecules.

• Explain the importance of water and its properties in biological systems.

• Identify the main chemical elements and macromolecules essential for life.

• Describe dehydration synthesis and hydrolysis reactions in macromolecule metabolism.

• Summarize the structure and function of carbohydrates, lipids, proteins, and nucleic acids.

Compounds in the Body

Inorganic Compounds

• Do not contain carbon (with some exceptions).

• Examples:

  • Water (H2O)

  • Salts

  • Acids and bases

Organic Compounds

• Contain carbon atoms, usually in combination with hydrogen, oxygen, and nitrogen.

• Examples: Biological macromolecules (carbohydrates, lipids, proteins, nucleic acids).

Water

Properties and Importance

• Most abundant inorganic compound in the body (60–80% of cell volume).

• Key properties:

  • High heat capacity: Absorbs and releases large amounts of heat with minimal temperature change.

  • High heat of vaporization: Requires significant energy to change from liquid to gas, aiding in cooling (e.g., sweating).

  • Polar solvent: Dissolves ionic and polar substances, facilitating chemical reactions and transport.

  • Reactivity: Participates in hydrolysis and dehydration synthesis reactions.

  • Cushioning: Protects organs by absorbing shock (e.g., cerebrospinal fluid).

Solubility and Amphipathic Molecules

• Hydrophilic: Substances that dissolve in water (e.g., salts, sugars).

• Hydrophobic: Substances that do not dissolve in water (e.g., fats, oils).

• Amphipathic: Molecules with both hydrophilic and hydrophobic regions (e.g., phospholipids).

Biological Macromolecules

General Features

• Large, complex molecules essential for life.

• Composed of repeating subunits called monomers.

• Four main classes: Carbohydrates, Lipids, Proteins, Nucleic Acids.

Polymerization Reactions

• Dehydration synthesis: Joins monomers by removing water.

  • General equation: $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + \text{H}_2\text{O}$

• Hydrolysis: Breaks polymers into monomers by adding water.

  • General equation: $\text{Polymer} + \text{H}_2\text{O} \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

Carbohydrates

Structure and Types

• Composed of C, H, O (general formula: (CH2O)n).

• Types:

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

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

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

Functions

• Main source of energy for cells (especially glucose).

• Some provide structural support (e.g., cellulose in plants).

• Storage forms: Glycogen (animals), starch (plants).

Lipids

Structure and Types

• Composed mainly of C, H, O (less O than carbohydrates).

• Types:

  • Fatty acids: Saturated (no double bonds), monounsaturated (one double bond), polyunsaturated (multiple double bonds).

  • Triglycerides: Three fatty acids + glycerol.

  • Phospholipids: Glycerol, two fatty acids, phosphate group (amphipathic).

  • Steroids: Four fused carbon rings (e.g., cholesterol, hormones).

Functions

• Energy storage (triglycerides).

• Cell membrane structure (phospholipids, cholesterol).

• Hormone production (steroids).

• Insulation and protection.

Table: Types of Fatty Acids

Type	Structure	State at Room Temp	Health Impact
Saturated	No double bonds	Solid	Excess may increase heart disease risk
Monounsaturated	One double bond	Liquid	Generally considered healthy
Polyunsaturated	Multiple double bonds	Liquid	Essential fatty acids, healthy in moderation

Proteins

Structure

• Composed of C, H, O, N (sometimes S).

• Monomers: Amino acids (20 types).

• Peptide bonds link amino acids into polypeptides.

Levels of Protein Structure

• Primary: Sequence of amino acids.

• Secondary: Alpha helices and beta-pleated sheets (hydrogen bonding).

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

• Quaternary: Multiple polypeptide chains (e.g., hemoglobin).

Functions

• Structural support (collagen, keratin).

• Enzymes (catalyze biochemical reactions).

• Transport (hemoglobin, membrane proteins).

• Movement (actin, myosin in muscles).

• Defense (antibodies).

• Communication (hormones, receptors).

Denaturation

• Loss of protein structure due to heat, pH, or chemicals.

• Usually reversible if normal conditions are restored, unless extreme.

• Denatured proteins lose function (e.g., cooked egg white).

Nucleic Acids

Structure

• Composed of C, H, O, N, P.

• Monomer: Nucleotide (phosphate group, sugar, nitrogenous base).

• Types: DNA (deoxyribonucleic acid), RNA (ribonucleic acid).

Functions

• Store and transmit genetic information.

• Direct protein synthesis.

• ATP (adenosine triphosphate): main energy currency of the cell.

ATP Structure and Function

• Composed of adenine, ribose, and three phosphate groups.

• Energy is stored in phosphate bonds; released by hydrolysis:

$\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

• ATP is produced mainly by cellular respiration (glycolysis, Krebs cycle, oxidative phosphorylation).

Summary Table: Major Biological Macromolecules

Macromolecule	Monomer	Main Elements	Functions	Examples
Carbohydrates	Monosaccharide	C, H, O	Energy, structure	Glucose, glycogen, starch
Lipids	Fatty acid, glycerol	C, H, O	Energy storage, membranes, hormones	Triglycerides, phospholipids, cholesterol
Proteins	Amino acid	C, H, O, N (S)	Structure, enzymes, transport, defense	Collagen, hemoglobin, antibodies
Nucleic Acids	Nucleotide	C, H, O, N, P	Genetic information, energy (ATP)	DNA, RNA, ATP

Key Terms and Concepts

• Monomer: Small building block molecule (e.g., glucose, amino acid).

• Polymer: Large molecule made of repeating monomers (e.g., starch, protein).

• Dehydration synthesis: Reaction joining monomers by removing water.

• Hydrolysis: Reaction breaking polymers by adding water.

• Amphipathic: Molecule with both hydrophilic and hydrophobic parts.

• ATP: Adenosine triphosphate, main energy carrier in cells.

Practice Questions (Selected)

• What type of chemical reaction is breakdown of maltose into glucose? (Hydrolysis)

• Which protein structure is achieved when alpha-helical and beta-pleated regions fold into a compact ball-like molecule? (Tertiary structure)

• Which macromolecule stores genetic information? (Nucleic acids)

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