Chapter 2: Chemistry Comes Alive – Study Notes for Anatomy & Physiology

Chapter 2: Chemistry Comes Alive

2.1 The Properties of an Element Depend on the Structure of Its Atoms

This section explores the fundamental building blocks of matter, focusing on atomic structure and its relevance to biological systems.

• Element: A substance that cannot be broken down into simpler substances by ordinary chemical means. Each element is defined by its number of protons.

• Major Elements in the Body: The four elements that form the bulk of body matter are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).

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

• Subatomic Particles: Atoms are composed of protons, neutrons, and electrons.

Particle	Charge	Mass (amu = Atomic mass unit)	Located in Nucleus?
Proton	+1	1	Yes
Neutron	0	1	Yes
Electron	-1	~0 (1/1836 of a proton)	No (orbitals/shells)

• Atomic Number: Number of protons in the nucleus.

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

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

Example: Carbon-12 and Carbon-14 are isotopes of carbon.

2.2 Atoms Bond Together to Form Molecules; Different Molecules Can Make Mixtures

Atoms interact to form molecules and mixtures, which are essential for biological structure and function.

• Molecule: Two or more atoms chemically bonded together (e.g., H2O).

• Mixture: Physical combination of two or more substances (e.g., air, blood plasma).

2.4 The Types of Chemical Bonds Are Ionic, Covalent, and Hydrogen

Chemical bonds hold atoms together in molecules and compounds. The main types are:

• Ionic Bonds: Formed when electrons are transferred from one atom to another, creating ions (e.g., NaCl).

• Covalent Bonds: Formed when atoms share electrons (e.g., O2, H2O).

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., between water molecules).

Electron Shells and the Octet Rule: Electrons occupy energy levels (shells) around the nucleus. Atoms are most stable when their outer shell is full (usually 8 electrons).

2.5 Chemical Reactions Occur When Electrons Are Shared, Gained, or Lost

Chemical reactions involve the making or breaking of bonds between atoms.

• Synthesis Reaction: Atoms or molecules combine to form a larger, more complex molecule. $A + B \rightarrow AB$

• Decomposition Reaction: A molecule is broken down into smaller molecules or atoms. $AB \rightarrow A + B$

• Exchange Reaction: Bonds are both made and broken. $AB + CD \rightarrow AD + CB$

Example: The formation of water from hydrogen and oxygen is a synthesis reaction.

2.6 Inorganic Compounds Include Water, Salts, and Many Acids and Bases

Inorganic compounds are essential for life and include water, salts, acids, and bases.

• Water: Most abundant inorganic compound in the body; excellent solvent.

• Salts: Ionic compounds that dissociate in water to form electrolytes.

• Acids and Bases: Acids release H+ ions; bases accept H+ ions.

• pH: A measure of hydrogen ion concentration; scale ranges from 0 (acidic) to 14 (basic), with 7 being neutral.

2.7 Organic Compounds Are Made by Dehydration Synthesis and Broken Down by Hydrolysis

Organic compounds contain carbon and are synthesized or broken down by specific reactions.

• Dehydration Synthesis: Joins monomers by removing water. $Monomer_1 + Monomer_2 \rightarrow Polymer + H_2O$

• Hydrolysis: Breaks polymers into monomers by adding water. $Polymer + H_2O \rightarrow Monomer_1 + Monomer_2$

2.8 Carbohydrates Provide an Easily Used Energy Source for the Body

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They are the body's primary energy source.

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

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

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

Example: Glycogen is the storage form of glucose in animals.

2.9 Lipids Insulate Body Organs, Build Cell Membranes, and Provide Stored Energy

Lipids are hydrophobic molecules that include fats, oils, and steroids.

• Triglycerides: Composed of glycerol and three fatty acids; main energy storage molecules.

• Phospholipids: Major component of cell membranes; contain a phosphate group.

• Steroids: Four fused carbon rings; include cholesterol and hormones.

2.10 Proteins Are the Body’s Basic Structural Material and Have Many Vital Functions

Proteins are polymers of amino acids and perform a wide variety of functions in the body.

• Amino Acids: Building blocks of proteins; 20 different types.

• Levels of Protein Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helices and beta sheets.

  • Tertiary: 3D folding of a single polypeptide.

  • Quaternary: Arrangement of multiple polypeptides.

• Enzymes: Proteins that catalyze biochemical reactions.

2.11 DNA and RNA Store, Transmit, and Help Express Genetic Information

Nucleic acids are polymers of nucleotides and include DNA and RNA.

• DNA: Stores genetic information; double helix structure.

• RNA: Involved in protein synthesis; single-stranded.

• Nucleotide: Composed of a sugar, phosphate group, and nitrogenous base.

Example: DNA replication and transcription are essential for cell division and protein synthesis.

2.12 ATP Transfers Energy to Other Compounds

ATP (adenosine triphosphate) is the primary energy carrier in cells.

• ATP Structure: Adenine base, ribose sugar, and three phosphate groups.

• ATP Function: Releases energy when its high-energy phosphate bonds are broken. $ATP \rightarrow ADP + P_i + \text{energy}$

Example: Muscle contraction and active transport use ATP as an energy source.