Module 1: Chemistry of Life – Foundations for Anatomy & Physiology

Module 1: Chemistry of Life

Introduction

The chemistry of life forms the foundation for understanding biological processes in Anatomy & Physiology. This module covers the structure of atoms, types of chemical bonds, properties of mixtures and solutions, the role of water, acids, bases, pH, and the importance of biological molecules such as ATP.

Atoms and Elements

Definition and Structure of Atoms

• Atom: The smallest unit of matter that retains the properties of an element.

• Atoms are the fundamental building blocks of all substances, including elements like carbon and sodium.

• Breaking down an atom further results in loss of the element's characteristic properties.

Example: A lump of carbon is composed entirely of carbon atoms; a block of sodium is composed of sodium atoms.

Subatomic Particles

• Protons: Positively charged particles found in the nucleus.

• Neutrons: Neutral particles also found in the nucleus.

• Electrons: Negatively charged particles orbiting the nucleus in electron shells.

• The number of protons defines the element; the number of electrons in a neutral atom equals the number of protons.

Electron Shells

• Electrons occupy energy levels called shells around the nucleus.

• The first shell holds up to 2 electrons; the second shell holds up to 8 electrons.

• Atoms are most stable when their outermost (valence) shell is full.

Mixtures and Solutions

Types of Mixtures

• Suspensions: Mixtures where solid particles are large enough to settle out (e.g., red blood cells in plasma).

• Colloids: Mixtures with particles too small to settle out (e.g., milk proteins in water).

• Solutions: Homogeneous mixtures where solutes are dissolved in a solvent (e.g., glucose in water).

Chemical Bonds

Valence Shells and Reactivity

• The valence shell is the outermost electron shell of an atom.

• Atoms with full valence shells are stable and unreactive (noble gases).

• Atoms with incomplete valence shells tend to form chemical bonds to achieve stability.

Ions, Cations, and Anions

• Ion: An atom or molecule with a net electric charge due to loss or gain of electrons.

• Cation: Positively charged ion (loss of electrons).

• Anion: Negatively charged ion (gain of electrons).

Ionic Bonds

• Formed by the transfer of electrons from one atom to another, resulting in attraction between oppositely charged ions.

• Example: Sodium (Na) donates an electron to chlorine (Cl), forming Na+ and Cl-, which attract to form NaCl (table salt).

Covalent Bonds

• Formed when two atoms share one or more pairs of electrons.

• Nonpolar covalent bond: Electrons are shared equally (e.g., H2 molecule).

• Polar covalent bond: Electrons are shared unequally due to differences in electronegativity (e.g., H2O molecule).

Hydrogen Bonds

• Weak attractions between the slightly positive hydrogen atom of one polar molecule and the slightly negative atom of another.

• Important in stabilizing the structure of water, proteins, and DNA.

Hydrophilic and Hydrophobic Molecules

• Hydrophilic: "Water-loving" molecules that dissolve easily in water (e.g., ions, polar molecules).

• Hydrophobic: "Water-fearing" molecules that do not dissolve in water (e.g., nonpolar molecules like oils).

Adenosine Triphosphate (ATP)

Structure and Function

• ATP: The primary energy carrier in cells.

• Composed of adenine (a nitrogenous base), ribose (a sugar), and three phosphate groups.

• Energy is stored in the bonds between phosphate groups, especially the third phosphate.

ATP Cycle

• ATP is formed from ADP (adenosine diphosphate) and inorganic phosphate (Pi) using energy from food.

• When ATP is hydrolyzed (broken down), it releases energy, ADP, and Pi:

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

• This process is reversible and central to cellular metabolism.

Acids, Bases, and pH

Hydrogen and Hydroxide Ions

• Water can dissociate into hydrogen ions (H+) and hydroxide ions (OH-).

• In pure water, [H+] = [OH-].

Acids

• Substances that release H+ ions in solution.

• Strong acids (e.g., HCl) completely dissociate in water.

• Weak acids (e.g., acetic acid) partially dissociate.

Bases

• Substances that release OH- ions or accept H+ ions.

• Strong bases (e.g., NaOH) completely dissociate in water.

• Weak bases (e.g., ammonia) partially dissociate or accept H+ ions.

Salts and Electrolytes

• Salt: An ionic compound formed from the reaction of an acid and a base (e.g., NaCl).

• Electrolytes: Compounds that dissociate into ions in solution, conducting electricity (e.g., Na+, K+, Ca2+, Cl-).

pH Scale

• pH measures the concentration of H+ ions in a solution.

• Defined as: $\text{pH} = -\log [\text{H}^+]$

• Scale ranges from 0 (most acidic) to 14 (most basic); pH 7 is neutral.

• Each unit change in pH represents a tenfold change in [H+].

Buffers

• Substances that minimize changes in pH by absorbing or releasing H+ ions.

• Critical for maintaining stable pH in body fluids (e.g., blood buffer system involving bicarbonate and carbonic acid).

• Example buffer reaction in blood:

$\text{H}^+ + \text{HCO}_3^- \leftrightarrow \text{H}_2\text{CO}_3$

• Buffers help prevent significant changes in blood pH, which is vital for normal cellular function.

Summary Table: Types of Chemical Bonds

Bond Type	How Formed	Example	Relative Strength
Ionic	Transfer of electrons between atoms	NaCl (table salt)	Strong (in solid state)
Covalent (Nonpolar)	Equal sharing of electrons	H2, O2	Very strong
Covalent (Polar)	Unequal sharing of electrons	H2O	Very strong
Hydrogen	Attraction between polar molecules	Between water molecules	Weak (individually)

Key Takeaways

• Understanding atomic structure and chemical bonding is essential for studying biological molecules and physiological processes.

• Water's unique properties, acids, bases, and pH regulation are fundamental to life and homeostasis.

• ATP is the universal energy currency in cells, driving nearly all cellular activities.