Key Concepts in Chemistry & Biochemistry for Anatomy & Physiology

Key Concepts in Chemistry & Biochemistry

Introduction

Chemistry and biochemistry are foundational to understanding anatomy and physiology. The chemical properties of matter, especially water, are essential for life and biological processes. Cells are composed primarily of water, and life’s chemistry is closely tied to water’s unique properties.

Defining Matter

States and Properties of Matter

• Matter: Anything that occupies space and has mass.

• Mass: The amount of matter in an object.

• States of Matter relevant to physiology:

  • Solids: Defined shape and volume.

  • Liquids: Defined volume, undefined shape.

  • Gases: Undefined shape and volume.

• Chemistry: The study of matter and how the building blocks of matter are put together.

Matter is Composed of Elements

Elements Essential for Human Life

• There are about 25 elements essential for human life.

• Major Elements (96.1% of body mass):

  • Oxygen (O)

  • Carbon (C)

  • Hydrogen (H)

  • Nitrogen (N)

• Minor Elements (3.9% of body mass):

  • Sodium (Na)

  • Chlorine (Cl)

  • Calcium (Ca)

  • Potassium (K)

  • Phosphorus, Sulfur, Magnesium, Iron, Iodine

• Trace Elements (less than 0.01% of body mass):

  • Copper, Zinc, Manganese, Cobalt, Chromium, Selenium, Molybdenum, Fluorine, Tin, Silicon, Vanadium

Example: Fluoride is added to water to prevent tooth decay; iodine is added to salt to prevent goiter.

Atoms and Subatomic Particles

Structure of the Atom

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

• Composed of three subatomic particles:

  • Protons: Positively charged, located in the nucleus.

  • Neutrons: No charge, located in the nucleus.

  • Electrons: Negatively charged, orbit the nucleus.

• Mass Number: Sum of protons and neutrons in the nucleus.

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

Ions: Cations and Anions

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

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

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

Example: Na+ (sodium ion) is a cation; Cl- (chloride ion) is an anion.

Chemical Bonds and Molecules

Types of Chemical Bonds

• Ionic Bonds: Complete transfer of electrons from one atom to another, resulting in oppositely charged ions that attract each other.

• Covalent Bonds: Atoms share electrons.

  • Non-polar Covalent: Electrons shared equally.

  • Polar Covalent: Electrons shared unequally, creating partial charges (polarity).

• Hydrogen Bonds: Weak attractions between a hydrogen atom in one molecule and an electronegative atom (like oxygen or nitrogen) in another.

Example: Water (H2O) molecules are held together by polar covalent bonds and form hydrogen bonds with each other.

Comparison of Bond Types

Bond Type	Electron Behavior	Strength	Example
Ionic	Transfer	Strong (in solid state)	NaCl (table salt)
Polar Covalent	Unequal sharing	Strong	H2O (water)
Non-polar Covalent	Equal sharing	Strong	O2 (oxygen gas)
Hydrogen	Attraction between polar molecules	Weak	Between water molecules

Chemical Reactions and Metabolism

Chemical Reactions

• Chemical Reaction: Process in which chemical bonds are formed, broken, or rearranged.

• Reactants: Starting substances.

• Products: Substances formed by the reaction.

• General equation: $\text{Reactants} \rightarrow \text{Products}$

Metabolism

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

• Anabolic Reactions: Build larger molecules from smaller ones; require energy.

• Catabolic Reactions: Break down larger molecules into smaller ones; release energy.

Solutions and Concentration

Definitions

• Solution: A homogeneous mixture of two or more substances.

• Solvent: The substance present in the greatest amount (usually water in physiology).

• Solute: Substances dissolved in the solvent (e.g., ions, glucose).

• Concentration: The amount of solute per volume of solution.

Properties of Water

Why Water is Essential for Life

• High Heat Capacity: Absorbs and releases heat slowly, helping maintain body temperature.

• High Heat of Vaporization: Evaporation of water requires significant energy, aiding in cooling (e.g., sweating).

• Polar Solvent Properties: Dissolves ionic and polar substances, facilitating chemical reactions and transport.

• Reactivity: Participates in many chemical reactions (e.g., hydrolysis, dehydration synthesis).

• Cushioning: Protects organs and tissues from physical trauma.

Acids, Bases, and pH

Definitions and Importance

• Acid: Substance that releases hydrogen ions (H+) in solution; proton donor.

• Base: Substance that accepts hydrogen ions or releases hydroxide ions (OH-); proton acceptor.

• pH: A measure of hydrogen ion concentration; scale ranges from 0 (most acidic) to 14 (most basic).

  • pH 7 is neutral (pure water).

  • pH < 7 is acidic; pH > 7 is basic (alkaline).

Equation: $\text{pH} = -\log_{10}[\text{H}^+]$

Organic and Inorganic Molecules

Classification

• Organic Molecules: Contain carbon, usually large, and held together by covalent bonds (e.g., carbohydrates, lipids, proteins, nucleic acids).

• Inorganic Molecules: Do not contain carbon (with some exceptions); include water, salts, acids, and bases.

Macromolecules of Life

Carbohydrates

• Composed of carbon, hydrogen, and oxygen (H:O ratio is 2:1).

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

• Disaccharides: Two monosaccharides joined by dehydration synthesis (e.g., sucrose, maltose, lactose).

• Polysaccharides: Long chains of monosaccharides (e.g., glycogen in animals).

Function: Provide energy and structural support.

Lipids

• Composed mostly of carbon and hydrogen; non-polar and insoluble in water.

• Triglycerides: Glycerol + 3 fatty acids; energy storage, insulation, cushioning.

• Phospholipids: Glycerol + 2 fatty acids + phosphate group; major component of cell membranes.

• Steroids: Four interlocking hydrocarbon rings (e.g., cholesterol, steroid hormones).

Proteins

• Composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.

• Polymers of amino acids (20 types); joined by peptide bonds.

• Structure: Sequence of amino acids determines protein shape and function.

• Functions: Enzymes, structural support, transport, signaling, movement, defense.

Nucleic Acids

• Polymers of nucleotides (sugar, phosphate, nitrogenous base).

• DNA (Deoxyribonucleic Acid): Double helix; stores genetic information.

• RNA (Ribonucleic Acid): Single strand; involved in protein synthesis.

Base Pairing in DNA: Adenine (A) pairs with Thymine (T); Guanine (G) pairs with Cytosine (C).

Polymerization Reactions

Dehydration Synthesis and Hydrolysis

• Dehydration Synthesis: Monomers are joined to form polymers by removing a water molecule.

• Hydrolysis: Polymers are broken down into monomers by adding a water molecule.

Summary Table: Major Classes of Biological Molecules

Class	Monomer	Polymer	Main Functions
Carbohydrates	Monosaccharide	Polysaccharide	Energy, structure
Lipids	Fatty acids, glycerol	Triglycerides, phospholipids, steroids	Energy storage, membranes, hormones
Proteins	Amino acid	Polypeptide	Enzymes, structure, transport
Nucleic Acids	Nucleotide	DNA, RNA	Genetic information, protein synthesis