General Biology: Foundations of Chemistry and Macromolecules Study Guide

Section 2.1: Matter, Elements, and Atoms

What is Matter?

Matter is anything that has mass and occupies space. All physical substances are composed of matter, which exists in three primary states: solid, liquid, and gas.

• Solid: Definite shape and volume.

• Liquid: Definite volume, but no definite shape.

• Gas: No definite shape or volume.

Elements and Compounds

An element is a pure substance consisting of only one type of atom. Examples include oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).

• Compound: A substance formed when two or more elements are chemically bonded together. Examples: water (H2O), carbon dioxide (CO2), glucose (C6H12O6).

Major Elements in the Human Body

Four elements make up about 96% of human body weight:

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

Trace elements such as iron (Fe) and iodine (I) are vital for processes like oxygen transport and thyroid function.

Atoms: Structure and Properties

An atom is the smallest unit of an element that retains its chemical properties. Atoms are composed of subatomic particles:

• Protons: Positively charged, found in the nucleus.

• Neutrons: Neutral charge, found in the nucleus.

• Electrons: Negatively charged, orbit the nucleus.

Atomic number is the number of protons in an atom. Mass number is the sum of protons and neutrons.

Isotopes and Radioactivity

Isotopes are atoms of the same element with different numbers of neutrons. Radioactive isotopes are unstable and decay over time, emitting radiation. Example: Carbon-14 is used in radiometric dating.

Electron Shells and Chemical Properties

Electrons are arranged in shells around the nucleus. The first shell holds up to 2 electrons, the second shell up to 8, and the third shell up to 8 electrons.

• The outermost shell is called the valence shell. If incomplete, atoms tend to react to achieve stability.

Section 2.2: Chemical Bonds and Molecules

Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules. The main types are:

• Covalent bonds: Atoms share electrons.

• Ionic bonds: Atoms transfer electrons, forming ions.

• Hydrogen bonds: Weak attractions between polar molecules.

Covalent and Ionic Bonds

• Covalent bond: A bond formed by sharing electrons between atoms. Example: H2O.

• Ionic bond: A bond formed by the transfer of electrons, resulting in oppositely charged ions. Example: NaCl (table salt).

Molecules and Electronegativity

A molecule is two or more atoms held together by covalent bonds. Electronegativity is an atom's ability to attract electrons in a bond.

• Polar covalent bond: Electrons are shared unequally (e.g., H2O).

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

Ions and Salts

An ion is an atom or molecule with a net electric charge due to loss or gain of electrons. Salts are compounds formed from ionic bonds, such as NaCl.

Section 2.16: Water and Its Properties

Hydrogen Bonds in Water

Hydrogen bonds form between the slightly positive hydrogen atom of one water molecule and the slightly negative oxygen atom of another. Water is a polar molecule due to its unequal sharing of electrons.

Cohesion, Adhesion, and Surface Tension

• Cohesion: Attraction between molecules of the same substance (e.g., water molecules sticking together).

• Adhesion: Attraction between molecules of different substances (e.g., water and glass).

• Surface tension: The measure of how difficult it is to stretch or break the surface of a liquid.

Heat, Temperature, and Evaporative Cooling

• Heat: Total energy of molecular motion.

• Temperature: Average kinetic energy of molecules.

• Evaporative cooling: As water evaporates, it removes heat, cooling the surface.

Ice and Water as Solvents

• Ice floats because it is less dense than liquid water, benefiting aquatic life.

• Solution: Homogeneous mixture of substances.

• Solvent: The dissolving agent (water is the universal solvent).

• Solute: The substance dissolved.

• Aqueous solution: Solution in which water is the solvent.

Chemical Reactions and Acids/Bases

• Chemical reaction: Bonds are broken and formed, converting reactants to products.

• Acid: Substance that increases hydrogen ion concentration.

• Base: Substance that reduces hydrogen ion concentration.

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

• Buffer: Substance that minimizes changes in pH, important in blood.

$2H_2 + O_2 \rightarrow 2H_2O$

Section 3.1: Organic Compounds and Macromolecules

Organic Compounds and Carbon Skeletons

Organic compounds are molecules containing carbon and hydrogen, often with other elements. Carbon can form four covalent bonds, allowing for diverse structures:

• Hydrocarbons: Molecules composed only of carbon and hydrogen. Can be straight, branched, or ring-shaped.

Isomers and Functional Groups

• Isomer: Molecules with the same molecular formula but different structures.

• Functional group: Specific group of atoms that imparts characteristic properties to organic molecules (e.g., hydroxyl, carboxyl).

Macromolecules and Polymers

Macromolecules are large molecules made of smaller subunits called monomers. Polymers are chains of monomers.

• Dehydration reaction: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

Section 3.2: Carbohydrates

Monosaccharides and Disaccharides

• Monosaccharide: Simple sugar, e.g., glucose ($C_6H_{12}O_6$).

• Disaccharide: Two monosaccharides joined together, e.g., sucrose.

Common monosaccharides: glucose, fructose, galactose.

Polysaccharides

• Starch: Storage polysaccharide in plants.

• Glycogen: Storage polysaccharide in animals.

• Cellulose: Structural polysaccharide in plants.

• Chitin: Structural polysaccharide in fungi and arthropods.

Section 3.3: Lipids

Characteristics and Types of Lipids

• Lipids: Hydrophobic molecules, including fats, phospholipids, and steroids.

• Fat molecule: Composed of glycerol and three fatty acids.

Saturated vs. Unsaturated Fats

Type	Structure	Properties
Saturated Fat	No double bonds	Solid at room temperature
Unsaturated Fat	One or more double bonds	Liquid at room temperature

Trans fats are artificially hydrogenated fats linked to cardiovascular disease.

Phospholipids and Steroids

• Phospholipid: Two fatty acids and a phosphate group; forms cell membranes.

• Cholesterol: A steroid important for membrane structure and hormone synthesis.

Section 3.4: Proteins and Nucleic Acids

Proteins: Structure and Function

• Monomer: Amino acid; 20 types.

• Peptide bond: Covalent bond between amino acids.

• Polypeptide: Chain of amino acids.

• Protein structure: Four levels—primary, secondary, tertiary, quaternary.

Protein Denaturation

• Excessive heat or pH changes can denature proteins, altering their shape and function.

Nucleic Acids: DNA and RNA

• DNA: Double-stranded, stores genetic information.

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

• Nucleotide: Monomer of nucleic acids, composed of a phosphate group, sugar, and nitrogenous base.

• Complementary base pairing: A-T (DNA), G-C (DNA and RNA), A-U (RNA).

R group in amino acids is called the side chain, which determines the properties of each amino acid.

Additional info: Some explanations and examples have been expanded for clarity and completeness.