LECTURE Chapter 2 – Better Living Through Chemistry - Part 1

Introduction to Chemistry in Anatomy & Physiology

Why Chemistry Matters in Physiology

Chemistry and biochemistry are essential for understanding physiological processes and for determining effective treatments for conditions such as dehydration and fluid loss. All bodily functions, from movement to digestion, rely on chemical reactions.

• Chemistry underlies all physiological reactions: Movement, digestion, heart function, and nervous system activity are all driven by chemical processes.

• Branches of Chemistry in Physiology:

  • Basic chemistry: Focuses on the fundamental principles of matter and energy.

  • Biochemistry: Examines the chemical processes within and related to living organisms.

Matter and Energy

Properties of Matter

Matter is the substance of the universe and is defined by its mass and the space it occupies.

• Matter: Anything that has mass and occupies space; can be seen, smelled, or felt.

• Weight: Mass plus the effects of gravity.

• States of Matter:

  • Solid: Definite shape and volume.

  • Liquid: Changeable shape, definite volume.

  • Gas: Changeable shape and volume.

Energy Concepts

Energy is the capacity to do work or move matter. The more work performed, the more energy is consumed.

• Energy: The ability to do work or put matter into motion.

• Forms of Energy:

  • Chemical energy: Stored in chemical bonds.

  • Electrical energy: Movement of charged particles.

  • Mechanical energy: Directly involved in moving matter.

  • Radiant/Electromagnetic energy: Travels in waves (e.g., heat, visible light, ultraviolet light, X-rays).

Atoms and Elements

Elements

Elements are pure substances that cannot be broken down by ordinary chemical means. They are the building blocks of matter.

• Major elements in the body: Carbon, oxygen, hydrogen, and nitrogen (make up 96% of body mass).

• 20 other elements are present in trace amounts.

• Periodic Table: Lists all known elements; 118 elements are recognized, most occur in nature.

Atoms

Atoms are the smallest units of an element that retain its properties. They are the fundamental building blocks of matter.

• Atomic symbol: One- or two-letter shorthand for each element (e.g., "O" for oxygen, "C" for carbon, "Na" for sodium).

Structure of Atoms

Subatomic Particles

Atoms are composed of three types of subatomic particles:

• Protons: Positive charge (+), 1 atomic mass unit (1 amu).

• Neutrons: No charge (0), 1 amu.

• Electrons: Negative charge (−), virtually no mass (0 amu).

Example: Hydrogen atom has 1 proton, 0 neutrons, and 1 electron.

Chemical Bonds and Reactions

Types of Chemical Bonds

Chemical bonds are energy relationships between electrons of reacting atoms. They determine the structure and function of molecules in the body.

• Ionic bonds: Formed by transfer of electrons from one atom to another, resulting in charged ions (cations and anions).

• Covalent bonds: Formed by sharing electrons between atoms; can be single, double, or triple bonds.

• Hydrogen bonds: Weak attractions between a hydrogen atom carrying a partial positive charge and another atom carrying a partial negative charge.

Electron Shells and Bonding

Electrons occupy energy levels called shells around the nucleus. The arrangement of electrons determines chemical reactivity.

• Shell 1: Holds up to 2 electrons.

• Shell 2: Holds up to 8 electrons.

• Shell 3: Holds up to 18 electrons.

• Valence shell: Outermost shell; electrons here are involved in chemical reactions.

• Octet rule: Atoms tend to have 8 electrons in their valence shell (except H and He, which have 2).

Chemically Inert and Reactive Elements

Elements with full valence shells are chemically inert (e.g., noble gases). Elements with incomplete valence shells are chemically reactive and tend to form bonds to achieve stability.

Summary Table: Major Chemical Bond Types

Bond Type	Strength	Key Features
Ionic	Intermediate	Transfer of electrons; forms ions; attraction between opposite charges
Covalent	Strongest	Sharing of electrons; may be polar (unequal sharing) or nonpolar (equal sharing)
Hydrogen	Weakest	Attraction between partial charges; important in water and biological molecules

Chemical Reactions

Chemical Equations

Chemical reactions involve the formation, rearrangement, or breaking of chemical bonds. They are represented by chemical equations.

• Reactants: Substances entering the reaction.

• Products: Substances produced by the reaction.

• Molecular formulas: Indicate the number and type of atoms (e.g., $H_2O$, $C_6H_{12}O_6$).

Types of Chemical Reactions

• Synthesis (Combination) Reactions: Atoms or molecules combine to form a larger, more complex molecule. Used in anabolic (building) processes. General equation: $A + B \rightarrow AB$

• Decomposition Reactions: Breakdown of a molecule into smaller molecules or atoms. Involve catabolic (bond-breaking) processes. General equation: $AB \rightarrow A + B$

• Exchange (Displacement) Reactions: Involve both synthesis and decomposition; bonds are made and broken. General equations: $AB + C \rightarrow AC + B$ or $AB + CD \rightarrow AD + CB$

• Redox (Oxidation-Reduction) Reactions: Involve transfer of electrons; atoms are reduced when they gain electrons and oxidized when they lose electrons. Example: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$

Energy Flow in Chemical Reactions

• Exergonic reactions: Release energy; products have less potential energy than reactants (e.g., catabolic and oxidative reactions).

• Endergonic reactions: Absorb energy; products have more potential energy than reactants (e.g., anabolic reactions).

Reversibility and Rate of Chemical Reactions

• Reversible reactions: Can proceed in both directions; equilibrium occurs when forward and reverse rates are equal.

• Factors affecting reaction rate:

  • Temperature: Higher temperature increases rate.

  • Concentration: Higher concentration increases rate.

  • Particle size: Smaller particles increase rate.

  • Catalysts: Increase reaction rate without being consumed; enzymes are biological catalysts.

Additional info: These foundational chemistry concepts are essential for understanding the molecular basis of physiological processes, including metabolism, cellular communication, and homeostasis.