Topic 2 Notes Study Guide

Basic Principles of Chemistry

Forms of Energy

Energy is essential for all biological processes, and it exists in several forms relevant to anatomy and physiology.

• Potential energy: Stored energy due to position or structure (e.g., a battery before use, water behind a dam).

• Kinetic energy: Energy of motion (e.g., a battery discharging, water falling).

• Chemical energy: Energy stored in chemical bonds and released when bonds are broken. Example: ATP hydrolysis in cells. $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

• Electrical energy: Energy from movement of electrons or ions, important in muscle and nerve function.

Chemical Bonds

Types of Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules and compounds. They are crucial for the structure and function of biological molecules.

• Ionic bonds: Formed by the complete transfer of one or more electrons from one atom to another, resulting in oppositely charged ions that attract each other. Example: Formation of sodium chloride (NaCl): Sodium atom (Na) loses an electron to become Na+, chlorine atom (Cl) gains an electron to become Cl-. Equation: $\text{Na} + \text{Cl} \rightarrow \text{Na}^+ + \text{Cl}^- \rightarrow \text{NaCl}$

• Covalent bonds: Formed when atoms share electrons. These are the most common bonds in organic molecules.

  • Non-polar covalent bonds: Electrons are shared equally (e.g., O2, H2).

  • Polar covalent bonds: Electrons are shared unequally, resulting in partial charges (e.g., H2O).

• Hydrogen bonds: Weak attractions between the slightly positive hydrogen atom of one molecule and the slightly negative atom (often oxygen or nitrogen) of another molecule. Example: Water molecules form hydrogen bonds, leading to high cohesion and surface tension.

Chemical Reactions

Types of Chemical Reactions in the Body

Chemical reactions involve the making or breaking of chemical bonds, resulting in the formation of new substances. They are fundamental to metabolism.

• Synthesis reactions (anabolism): Building larger molecules from smaller ones. Requires energy (endergonic). $\text{A} + \text{B} + \text{energy} \rightarrow \text{AB}$

• Dehydration synthesis: A type of synthesis reaction that releases water. $\text{A-OH} + \text{HB} + \text{energy} \rightarrow \text{AB} + \text{H}_2\text{O}$

• Decomposition reactions (catabolism): Breaking down larger molecules into smaller units. Releases energy (exergonic). $\text{CD} \rightarrow \text{C} + \text{D} + \text{energy}$

• Hydrolysis reactions: Decomposition reactions that require water. $\text{CD} + \text{H}_2\text{O} \rightarrow \text{COH} + \text{HD} + \text{energy}$

• Exchange reactions: Involve both synthesis and decomposition; parts of molecules are exchanged. $\text{AB} + \text{CD} \rightarrow \text{AC} + \text{BD}$

Metabolism is the sum of all chemical reactions in the body, including both anabolic (building up) and catabolic (breaking down) processes.

Energy Flow in Chemical Reactions

Chemical reactions involve energy changes, either absorbing (endergonic) or releasing (exergonic) energy. Coupled reactions in metabolism allow energy released from one reaction to drive another.

Important Inorganic Compounds

Inorganic vs. Organic Compounds

Compounds in the body are classified as inorganic or organic based on their composition and structure.

• Inorganic compounds: Usually do not contain carbon; include water, salts, acids, bases.

• Organic compounds: Contain carbon and usually hydrogen; include carbohydrates, lipids, proteins, nucleic acids.

Water: Properties and Importance

Water is the most abundant inorganic compound in the body and is vital for life.

• Solvent properties: Water dissolves many substances due to its polarity, facilitating chemical reactions and transport.

• Transport: Water helps move substances throughout the body and between cells and tissues.

• High heat capacity: Water absorbs and releases heat slowly, helping maintain body temperature.

• High heat of vaporization: Water requires significant energy to change from liquid to gas, aiding in cooling mechanisms like sweating.

• Protection: Water provides cushioning and lubrication for organs and tissues.

Acids, Bases, and Salts

These compounds are important for maintaining pH balance and electrolyte levels in the body.

• Acids: Dissociate in water to release hydrogen ions (H+). $\text{HCl} \rightarrow \text{H}^+ + \text{Cl}^-$ $\text{H}_2\text{SO}_4 \rightarrow 2\text{H}^+ + \text{SO}_4^{2-}$

• Bases: Dissociate in water to release hydroxide ions (OH-). $\text{NaOH} \rightarrow \text{Na}^+ + \text{OH}^-$

• Salts: Formed when acids and bases react together; dissociate into ions other than H+ or OH-. $\text{NaCl} \rightarrow \text{Na}^+ + \text{Cl}^-$

Many salts in the body are formed by neutralization reactions: $\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}$

Summary Table: Types of Chemical Bonds

Bond Type	Description	Example	Biological Importance
Ionic	Transfer of electrons, forms ions	NaCl (table salt)	Electrolyte balance, nerve impulses
Covalent	Sharing of electrons	H2O, O2, CH4	Structure of organic molecules
Hydrogen	Weak attraction between polar molecules	Between water molecules	Cohesion, surface tension, DNA structure

Summary Table: Types of Chemical Reactions

Reaction Type	Description	General Equation	Example
Synthesis (Anabolism)	Builds larger molecules from smaller units	$A + B + \text{energy} \rightarrow AB$	Protein synthesis
Decomposition (Catabolism)	Breaks down larger molecules into smaller units	$CD \rightarrow C + D + \text{energy}$	Digestion of food
Exchange	Parts of molecules are exchanged	$AB + CD \rightarrow AC + BD$	Phosphate transfer in ATP

Key Terms and Definitions

• Atom: The smallest unit of an element, consisting of protons, neutrons, and electrons.

• Element: A pure substance made of only one kind of atom.

• Molecule: Two or more atoms bonded together.

• Compound: A substance formed from two or more different elements bonded together.

• Electrolyte: A substance that dissociates into ions in solution and conducts electricity.

• Solvent: The substance in which solutes are dissolved (water is the universal solvent in biology).

• Solute: The substance dissolved in a solvent.

• Metabolism: The sum of all chemical reactions in the body.

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