Chemical Reactions: The Foundation of All Life Processes

Overview of Chemical Reactions

Chemical reactions are essential for all biological activities, as they involve the formation and breaking of chemical bonds. Understanding these reactions is crucial for studying Anatomy & Physiology.

• Reactants: The initial substances involved in a chemical reaction.

• Products: The final substances formed after a chemical reaction.

• Metabolism: The sum of all chemical reactions occurring in an organism, including both anabolic (building up) and catabolic (breaking down) processes.

Forms of Energy and Chemical Reactions

• Energy: The capacity to do work.

  • Potential energy: Stored energy (e.g., battery, dam).

  • Kinetic energy: Energy released or associated with matter in motion (e.g., hitting a baseball).

  • Chemical energy: A form of potential energy stored in the bonds of molecules (e.g., ATP, glucose).

• Energy Transfer in Chemical Reactions: Breaking chemical bonds releases energy, while forming new bonds requires energy.

• Exergonic reactions: Release more energy than they consume (e.g., catabolic reactions).

• Endergonic reactions: Consume more energy than they release (e.g., anabolic reactions).

Activation Energy and Catalysts

• Activation energy: The initial energy needed to start a reaction, usually to break chemical bonds in reactants.

• Catalysts: Chemical compounds that speed up reactions by lowering the activation energy required. Enzymes are biological catalysts.

Types of Chemical Reactions

• Synthesis reactions: Two or more atoms, ions, or molecules combine to form new, larger molecules. These are anabolic reactions. Example: Formation of ATP.

• Decomposition reactions: A molecule is broken down into smaller parts. These are catabolic reactions. Example: Breakdown of glucose during cellular respiration.

• Exchange reactions: Atoms are shuffled between molecules to form new products.

• Reversible reactions: Can proceed in either direction, depending on conditions.

Inorganic Compounds and Solutions

Inorganic Compounds

Inorganic compounds are generally simple molecules that do not contain both carbon and hydrogen. Water, salts, acids, and bases are key examples.

Mixtures and Solutions

• Solution: A solute is dissolved in a solvent (e.g., salt water).

• Colloid: Contains larger particles than a solution but does not settle out (e.g., milk).

• Suspension: Contains even larger particles that may settle out over time (e.g., blood).

Water: Properties and Functions

• Solvent: Water is the universal solvent, dissolving many substances necessary for life.

• High heat capacity: Water absorbs and retains heat, helping to regulate body temperature.

• High heat of vaporization: Water requires a lot of energy to change from liquid to gas, aiding in cooling (e.g., sweating).

• Lubricant: Water reduces friction in joints and body cavities.

• Reactivity: Water participates in hydrolysis (breaking bonds with water) and dehydration synthesis (removing water to form bonds).

• Cohesion and adhesion: Water molecules stick to each other (cohesion) and to other substances (adhesion), contributing to surface tension.

Acids, Bases, and pH

Definitions and Properties

• Acid: A substance that dissociates in solution to release H+ ions.

• Base: A substance that dissociates in solution to release OH- ions or accept H+ ions.

• pH: The negative logarithm of the hydrogen ion concentration.

  • pH 7 is neutral; pH < 7 is acidic; pH > 7 is basic.

• Buffers: Compounds that stabilize pH by removing or replacing H+ ions (e.g., HCO3-, NaHCO3).

Organic Compounds

General Characteristics

Organic compounds always contain carbon and hydrogen, usually contain oxygen, and always have covalent bonds. They make up about 40% of body mass and are essential for complex functions.

Carbohydrates (CHO)

Carbohydrates are the primary source of energy for the body. They are classified based on the number of sugar units:

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

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

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

Lipids

Lipids are hydrophobic molecules that provide energy storage, insulation, and protection. Major types include:

• Triglycerides: Composed of a glycerol backbone and three fatty acids. Can be solid (fats) or liquid (oils) at room temperature.

• Phospholipids: Major component of cell membranes, with hydrophilic heads and hydrophobic tails.

• Steroids: Include cholesterol, which is important for membrane structure and as a precursor for steroid hormones.

• Eicosanoids: Lipid-derived signaling molecules (e.g., prostaglandins) involved in inflammation and other physiological responses.

Proteins

Proteins are polymers of amino acids and perform a wide range of functions, including structural support, catalysis (enzymes), transport, and immune defense.

• Amino acids: Building blocks of proteins, containing C, H, O, N, and sometimes S.

• Peptides and polypeptides: Chains of amino acids joined by peptide bonds.

• Enzymes: Biological catalysts that speed up chemical reactions by lowering activation energy. Enzyme names often end in -ase (e.g., protease, lipase, ATPase).

Nucleic Acids

Nucleic acids store and transmit genetic information. Two main types:

• Deoxyribonucleic acid (DNA): Contains genetic instructions for development and function.

• Ribonucleic acid (RNA): Involved in protein synthesis and gene regulation.

Adenosine Triphosphate (ATP)

ATP is the primary energy currency of the cell. It stores energy in high-energy phosphate bonds.

• When ATP is hydrolyzed to ADP and inorganic phosphate (Pi), energy is released for cellular processes.

• Equation:

• ATP is used for muscle contraction, active transport, synthesis reactions, and more.