Chemistry of Life and Macromolecules

Introduction

This section explores the foundational chemistry concepts essential for understanding Anatomy & Physiology, focusing on chemical bonds, chemical reactions, and the structure and function of organic macromolecules such as carbohydrates, lipids, proteins, and nucleic acids.

Chemical Bonds and Reactions

Types of Chemical Bonds

• Ionic Bonds: Formed when electrons are transferred from a metal to a non-metal, resulting in oppositely charged ions that attract each other. Example: NaCl (table salt).

• Covalent Bonds: Formed when atoms share electrons. These are stronger than ionic bonds and can be:

  • Non-polar Covalent Bonds: Electrons are shared equally (e.g., O2, CO2).

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

• Hydrogen Bonds: Weak attractions between a partially positive hydrogen atom and a partially negative atom (usually oxygen or nitrogen) in another molecule. These are not true bonds but are crucial for the properties of water and biological molecules.

Chemical Reactions

• Reactants: Substances that enter into a chemical reaction.

• Products: Substances produced by a chemical reaction.

• Synthesis (Anabolic) Reactions: Two or more reactants combine to form a larger product. Example:

• Decomposition (Catabolic) Reactions: A reactant breaks down into smaller products. Example:

Enzymes

• Enzymes: Biological catalysts, mostly proteins, that speed up chemical reactions by lowering activation energy. They are essential for metabolism and cellular function.

Organic Macromolecules

Monomers and Polymers

• Monomers: Small, single subunits that can join together to form larger molecules.

• Polymers: Large molecules made by linking monomers together.

• Dehydration Synthesis: Chemical reaction that joins monomers by removing a water molecule. Products: polymer + H2O

• Hydrolysis: Chemical reaction that breaks polymers into monomers using water as a reactant. Products: monomers

Carbohydrates

Structure and Function

• Main source of energy for cells (glucose is converted to ATP).

• Form glycoproteins and glycolipids in cell membranes.

Types of Carbohydrates

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

• Disaccharides: Two monosaccharides joined by a glycosidic bond (e.g., sucrose, maltose, lactose).

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

Lipids

Structure and Function

• Composed mainly of nonpolar hydrocarbons; hydrophobic (insoluble in water).

• Major types: triglycerides, phospholipids, steroids.

Fatty Acids

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

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

  • Monounsaturated: One double bond.

  • Polyunsaturated: Two or more double bonds (e.g., omega-3 fatty acids).

Triglycerides

• Formed by joining three fatty acids to a glycerol molecule via dehydration synthesis.

• Functions: energy storage, insulation, protection of organs, absorption of fat-soluble vitamins.

Phospholipids

• Composed of a glycerol backbone, two fatty acids (hydrophobic), and a phosphate group (hydrophilic).

• Main component of cell membranes; act as emulsifiers.

Steroids

• Structure: Four fused hydrocarbon rings.

• Functions: Components of cell membranes (cholesterol), hormones, bile acids.

Proteins

Structure and Function

• Functions: Enzymes, structural support, transport, signaling, immune response, acid-base balance.

Amino Acids

• Monomers of proteins; each contains a central carbon, hydrogen, amino group, carboxyl group, and variable R group.

Peptide Bonds and Protein Structure

• Peptide bonds form between amino acids via dehydration synthesis.

• Proteins have four levels of structure:

  • Primary: Sequence of amino acids.

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

  • Tertiary: Overall 3D shape of a single polypeptide.

  • Quaternary: Assembly of multiple polypeptide chains.

Nucleic Acids and Nucleotides

Nucleotides

• Monomers of nucleic acids; each consists of a phosphate group, a pentose sugar (ribose or deoxyribose), and a nitrogenous base (adenine, guanine, cytosine, thymine, or uracil).

DNA and RNA

• DNA: Double-stranded, stores genetic information, uses complementary base pairing, held together by phosphodiester and hydrogen bonds.

• RNA: Single-stranded, involved in protein synthesis and gene regulation, contains uracil instead of thymine.

Adenosine Triphosphate (ATP)

• Structure: Ribose sugar, adenine base, and three phosphate groups.

• Function: Main energy currency of the cell; energy is stored in the high-energy phosphate bonds and released during hydrolysis.

Summary Table: Major Macromolecules