Lecture 7

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Chemical Reactions in Human Anatomy and Physiology

Introduction to Chemical Reactions

Chemical reactions are fundamental to the structure and function of living cells. In Anatomy & Physiology, understanding how chemical bonds form and break is essential for grasping cellular processes and energy flow.

Chemical reaction: A process in which substances (reactants) are transformed into new substances (products) by breaking and forming chemical bonds.
Chemical notation: The symbolic representation of chemical reactions, typically using chemical formulas and symbols.
Chemical equation: An expression showing the reactants and products of a chemical reaction. Example:
Reactants: Substances present at the start of a reaction (left side of the equation).
Products: Substances formed as a result of the reaction (right side of the equation).

Types of Chemical Reactions

Chemical reactions can be classified based on their reversibility and energy changes.

Reversible reactions: Reactions that can proceed in both directions, forming reactants from products and vice versa. Example:
Irreversible reactions: Reactions that proceed in one direction only, with products not reverting to reactants under normal conditions. Example:

Bonds in Cells

Major Biological Macromolecules

Cells are composed of four major types of biological macromolecules, each with distinct roles in cellular structure and function.

Proteins: Most numerous macromolecules; perform a wide variety of cellular functions including catalysis, structure, transport, and signaling.
Carbohydrates: Sugars and polysaccharides; provide energy and structural support.
Lipids: Fats, oils, and steroids; important for energy storage, membrane structure, and signaling.
Nucleic acids: DNA and RNA; store and transmit genetic information.

Protein Structure and Bonding

Proteins are the most abundant molecules in cells and are crucial for nearly all cellular functions. Their structure and charge are essential for their function, and proper folding is maintained by various types of chemical bonds.

Primary structure: Sequence of amino acids linked by peptide bonds.
Secondary structure: Regular patterns (e.g., alpha helices, beta sheets) stabilized by hydrogen bonds.
Tertiary structure: Three-dimensional folding driven by interactions such as ionic bonds, hydrophobic interactions, and disulfide bridges.
Quaternary structure: Association of multiple polypeptide chains.
Proper folding: Essential for protein function; misfolding can lead to loss of function or disease.

Examples of Chemical Bonds in Cells

Chemical bonds are responsible for the structure and function of macromolecules. The slide shows examples of bond formation:

NaF (Sodium Fluoride): Example of an ionic bond between sodium (Na+) and fluoride (F-).
F2 (Fluorine gas): Example of a covalent bond between two fluorine atoms.
HF (Hydrogen Fluoride): Example of a polar covalent bond between hydrogen and fluorine.

Additional info: Ionic bonds involve the transfer of electrons, covalent bonds involve sharing of electrons, and polar covalent bonds have unequal sharing of electrons.

Energy and Chemical Reactions

Forms of Energy in Biological Systems

Energy is the capacity to do work or put matter into motion. Chemical reactions in cells involve changes in energy, which can be classified as follows:

Potential energy: Stored energy that can be released to do work. Example: Energy stored in chemical bonds.
Kinetic energy: Energy of motion; released potential energy that is used to perform work. All atoms possess kinetic energy due to constant motion.
Chemical energy: Energy stored in chemical bonds; released during chemical reactions.
Electrical energy: Energy from movement of charged particles (ions); important in nerve impulses and muscle contraction.
Mechanical energy: Energy directly involved in moving matter; used by motor proteins like kinesin to move along microtubules.

Example: Kinesin uses mechanical energy to transport cellular cargo along microtubules.

Summary Table: Major Biological Macromolecules

Macromolecule	Main Components	Function	Example
Proteins	Amino acids	Catalysis, structure, transport	Enzymes, hemoglobin
Carbohydrates	Monosaccharides	Energy, structure	Glucose, cellulose
Lipids	Fatty acids, glycerol	Energy storage, membranes	Triglycerides, cholesterol
Nucleic acids	Nucleotides	Genetic information	DNA, RNA

Additional info: This table summarizes the main types of macromolecules found in cells, their building blocks, functions, and examples.