Chapter 2: Chemistry Comes Alive

2-1 Matter and Energy

Understanding matter and energy is essential for grasping the chemical basis of life processes in Anatomy & Physiology. Matter is anything that occupies space and has mass, while energy is the capacity to do work.

• States of Matter:

  • Solid: Definite shape and volume.

  • Liquid: Definite volume; shape of container.

  • Gas: Neither definite shape nor volume.

• Physical vs. Chemical Changes:

  • Physical changes: Do not alter the basic nature of a substance (e.g., melting ice).

  • Chemical changes: Alter the chemical composition of a substance (e.g., burning wood).

• Energy:

  • Kinetic energy: Energy in motion, performing work.

  • Potential energy: Stored energy, not currently doing work.

• Forms of Energy:

  • Chemical energy: Stored in chemical bonds (e.g., ATP).

  • Electrical energy: Movement of charged particles (e.g., nerve impulses).

  • Mechanical energy: Directly involved in moving matter (e.g., muscle contraction).

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

• Energy Conversion:

  • Chemical energy from food is stored in ATP and can be converted to mechanical or electrical energy in the body.

2-2 Body Composition

The human body is composed of elements, which are the fundamental units of all matter. Elements cannot be broken down into smaller units by chemical means and may exist as single atoms or as molecules made of identical atoms.

• Elements:

  • Examples: Oxygen (O2) is essential for cellular respiration.

  • The periodic table lists all known elements, each with a unique chemical symbol.

• Major Elements in the Body:

  • Oxygen (O): Essential for cellular respiration and ATP production.

  • Carbon (C): Primary element in organic molecules (carbohydrates, lipids, proteins, nucleic acids).

  • Hydrogen (H): Major component in most organic molecules; influences pH as an ion.

  • Nitrogen (N): Major component of proteins and nucleic acids.

• Trace Elements:

  • Required in small amounts for specific physiological functions (e.g., calcium for muscle contraction, iron for oxygen transport).

Periodic Table: Classification and Identification

The periodic table organizes elements by atomic number and chemical properties. Each element is represented by a chemical symbol, often derived from its name (e.g., C for carbon, Na for sodium).

2-3 Composition of Matter

Atoms are the building blocks of elements. Each atom is unique and consists of subatomic particles.

• Subatomic Particles:

  • Protons (p+): Positively charged, located in the nucleus.

  • Neutrons (n0): Uncharged, located in the nucleus.

  • Electrons (e-): Negatively charged, orbit the nucleus.

• Atomic Number: Number of protons in the nucleus; identifies the element.

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

• Atoms are electrically neutral: Number of protons equals number of electrons.

• Ions: Atoms that have lost (cation, positive) or gained (anion, negative) electrons.

2-4 Isotopes and Atomic Weight

Isotopes are natural variations of elements with the same number of protons but different numbers of neutrons.

• Isotopes:

  • Examples: Hydrogen has three isotopes—protium, deuterium, and tritium.

• Atomic Weight:

  • Average mass of all isotopes of an element.

• Radioisotopes:

  • Unstable isotopes that decay, emitting particles and energy (radioactivity).

  • Used in medical imaging (e.g., PET scans).

2-5 Molecules, Compounds, and Mixtures

Molecules and compounds are formed by chemical bonding, while mixtures are physical combinations of substances.

• Molecule: Two or more atoms of the same element bonded together (e.g., O2).

• Compound: Two or more atoms of different elements bonded together (e.g., H2O).

• Mixture: Physical combination of substances without chemical bonding.

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

  • Colloids: Particles do not settle out, form gels (e.g., cytoplasm).

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

• Comparison Table:

2-6 Chemical Reactions

Chemical reactions involve the making or breaking of chemical bonds, resulting in new substances.

• Synthesis Reaction: Smaller particles are bonded to form larger, more complex molecules. Example: Amino acids join to form proteins.

• Decomposition Reaction: Bonds in larger molecules are broken to form smaller, less complex molecules. Example: Glycogen breaks down to release glucose.

• Exchange Reaction: Bonds are both made and broken; parts of molecules are exchanged. Example: ATP transfers a phosphate group to glucose.

• Factors Affecting Reaction Rate:

  • Temperature: Higher temperature increases reaction rate.

  • Concentration: Higher concentration increases reaction rate.

  • Particle Size: Smaller particles increase reaction rate.

  • Catalysts: Lower activation energy, increasing reaction rate.

2-7 Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules and compounds.

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

• Covalent Bonds: Formed by sharing electrons between atoms.

  • Nonpolar covalent: Electrons shared equally (e.g., O2).

  • Polar covalent: Electrons shared unequally, creating poles (e.g., H2O).

• Hydrogen Bonds: Weak bonds between polar molecules, important for water properties and biological molecules (e.g., DNA, proteins).

2-8 Organic and Inorganic Compounds

Compounds in the body are classified as organic (contain carbon) or inorganic (do not contain carbon).

• Inorganic Compounds:

  • Water: Most abundant; high heat capacity, solvent, reactivity, cushioning.

  • Salts: Dissociate into ions; essential for nerve impulses and muscle contraction.

  • Acids and Bases: Release H+ or OH-; important for pH balance.

• Organic Compounds:

  • Carbohydrates: Energy source; monomers are simple sugars.

  • Lipids: Energy storage, cell membranes; includes triglycerides, phospholipids, steroids, eicosanoids.

  • Proteins: Structure and function; made of amino acids, have four structural levels.

  • Nucleic Acids: DNA and RNA; genetic information and protein synthesis.

2-9 pH and Buffer Systems

pH measures the concentration of hydrogen ions in a solution, indicating its acidity or basicity.

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

• Buffers: Chemicals that resist changes in pH, maintaining homeostasis.

2-10 Synthesis and Hydrolysis Reactions

Organic molecules are built and broken down by dehydration synthesis and hydrolysis reactions.

• Dehydration Synthesis: Monomers join to form polymers by removing water.

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

2-11 Carbohydrates

Carbohydrates are organic molecules containing carbon, hydrogen, and oxygen. They are classified by size and function.

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

• Disaccharides: Two monosaccharides joined (e.g., sucrose, lactose).

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

2-12 Lipids

Lipids are diverse organic molecules, insoluble in water, and serve as energy storage and structural components.

• Triglycerides: Three fatty acids + glycerol; energy storage.

• Saturated Fats: Single bonds; solid at room temperature.

• Unsaturated Fats: Double bonds; liquid at room temperature.

• Phospholipids: Form cell membranes; polar head and nonpolar tails.

• Steroids: Four-ring structure; includes cholesterol, hormones.

• Eicosanoids: Derived from fatty acids; involved in inflammation and other functions.

2-13 Proteins

Proteins are polymers of amino acids and perform structural and functional roles in the body.

• Structural Proteins: Provide support (e.g., collagen, keratin).

• Functional Proteins: Act as enzymes, antibodies, hormones.

• Levels of Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Coils and folds (alpha-helix, beta-sheet).

  • Tertiary: 3D shape due to R group interactions.

  • Quaternary: Multiple polypeptide chains (e.g., hemoglobin).

• Denaturation: Loss of structure and function due to chemicals, temperature, or pH changes.

2-14 Enzymes

Enzymes are proteins that act as biological catalysts, speeding up chemical reactions by lowering activation energy.

• Substrate: The molecule upon which an enzyme acts.

• Active Site: Region where substrate binds and reaction occurs.

• Enzyme-Substrate Complex: Temporary association during reaction.

2-15 Nucleic Acids and ATP

Nucleic acids store and transmit genetic information, while ATP is the primary energy carrier in cells.

• DNA: Double-stranded helix; contains genetic instructions.

• RNA: Single-stranded; involved in protein synthesis.

• ATP (Adenosine Triphosphate):

  • Composed of adenine, ribose, and three phosphate groups.

  • Energy is released by breaking high-energy phosphate bonds:

  • ATP is replenished by oxidation of food fuels (e.g., glucose).

Summary Table: Major Organic Molecules

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