The Chemistry of Life: Foundations for Anatomy & Physiology

Chapter Overview: The Chemistry of Life

Introduction

Chemistry is fundamental to understanding anatomy and physiology because all living organisms are composed of chemical substances. This chapter explores the atomic and molecular basis of life, focusing on elements, atoms, chemical bonds, mixtures, and chemical reactions as they relate to the human body.

Atoms and Elements

Definition of Matter and Elements

• Matter: Anything that has mass and occupies space.

• Element: A pure substance consisting of only one type of atom; cannot be broken down into simpler substances by chemical means.

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

Atomic Structure

• Atoms are composed of three subatomic particles:

  • Protons: Positively charged, found in the nucleus.

  • Neutrons: No charge, found in the nucleus.

  • Electrons: Negatively charged, orbit the nucleus.

• Atomic number: Number of protons in the nucleus.

• Mass number: Sum of protons and neutrons.

• Atoms are electrically neutral when the number of protons equals the number of electrons.

Electron Shells

• Electrons occupy energy levels called shells.

• First shell holds up to 2 electrons; second shell up to 8; third shell up to 18 (but is stable with 8).

Elements in the Periodic Table and the Human Body

Major Elements in the Human Body

• Four major elements make up 96% of the body’s mass:

  • Oxygen (O)

  • Carbon (C)

  • Hydrogen (H)

  • Nitrogen (N)

• Other important elements: Calcium (Ca), Phosphorus (P), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), Magnesium (Mg), Iron (Fe).

Periodic Table

• Organizes elements by atomic number and properties.

• Groups elements with similar chemical behaviors.

Isotopes and Radioactivity

Isotopes

• Atoms of the same element with different numbers of neutrons.

• Some isotopes are radioactive and decay over time, emitting radiation.

Applications

• Nuclear Medicine: Uses radioactive isotopes for diagnosis and treatment (e.g., cancer radiation therapy).

Matter Combined: Mixtures and Chemical Bonds

Mixtures

• Combinations of two or more substances physically blended but not chemically bonded.

• Three types:

  • Suspensions: Large particles settle out (e.g., blood cells in plasma).

  • Colloids: Small particles remain dispersed (e.g., cytoplasm).

  • Solutions: Homogeneous mixtures (e.g., salt water).

Chemical Bonds

• Forces that hold atoms together in molecules and compounds.

• Three main types:

  • Ionic Bonds: Electrons are transferred from one atom to another, forming ions (charged atoms).

  • Covalent Bonds: Electrons are shared between atoms.

  • Hydrogen Bonds: Weak attractions between polar molecules, important in water and biological molecules.

Ions and Ionic Bonds

Formation of Ions

• Atoms gain or lose electrons to achieve stability, forming ions.

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

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

Ionic Bonding

• Occurs between metals and nonmetals.

• Example: Sodium (Na) transfers an electron to Chlorine (Cl), forming Na+ and Cl- ions, which attract each other to form NaCl (table salt).

Covalent Bonds

Types of Covalent Bonds

• Nonpolar Covalent Bonds: Electrons are shared equally (e.g., O2 molecule).

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

Electron Sharing Table

Electron sharing in covalent bonds can be summarized as follows:

Bond Type	Electron Sharing	Example
Single	1 pair	H-H
Double	2 pairs	O=O
Triple	3 pairs	N≡N

Hydrogen Bonds

Properties and Importance

• Weak attractions between partially charged regions of polar molecules.

• Responsible for surface tension in water and stabilization of biological molecules (e.g., DNA).

Chemical Notation and Reactions

Chemical Notation

• Symbols represent elements and compounds.

• Formulas show the number and types of atoms in molecules.

• Reactions are written as: $\text{Reactants} \rightarrow \text{Products}$

Types of Chemical Reactions

• Synthesis (Anabolic) Reactions: Build larger molecules from smaller ones. $A + B \rightarrow AB$

• Decomposition (Catabolic) Reactions: Break down molecules into smaller components. $AB \rightarrow A + B$

• Exchange Reactions: Rearrangement of parts between molecules. $AB + CD \rightarrow AD + CB$

Energy and Chemical Reactions

Forms of Energy

• Chemical Energy: Stored in chemical bonds.

• Electrical Energy: Movement of charged particles.

• Mechanical Energy: Directly moves matter.

• Radiant Energy: Travels in waves (e.g., light).

Activation Energy

• Energy required to start a chemical reaction.

• Enzymes lower activation energy, speeding up reactions in the body.

Homeostasis and Chemical Reactions

Role of Chemical Reactions in Homeostasis

• Metabolic reactions maintain the internal environment of the body.

• Catabolic reactions release energy; anabolic reactions use energy to build complex molecules.

Summary Table: Types of Chemical Bonds

Bond Type	Description	Example
Ionic	Transfer of electrons	NaCl
Covalent	Sharing of electrons	H2O, O2
Hydrogen	Weak attraction between polar molecules	Between water molecules

Additional info:

• Enzymes are biological catalysts that are crucial for maintaining homeostasis by regulating the speed of chemical reactions.

• Radioactive isotopes are used in medical imaging and cancer therapy.