General Biology Study Guide: Chemical Context and Molecular Diversity of Life

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Chapter 2: The Chemical Context of Life

Chemical Elements and Compounds

Understanding the basic chemical principles is essential for studying biological systems. Elements and compounds form the foundation of all matter.

Element: A substance that cannot be broken down into simpler substances by chemical means.
Compound: A substance composed of two or more different elements chemically combined in fixed ratios.
Example: Water (H2O) is a compound made of hydrogen and oxygen.

Exploring Life on Its Many Levels

Life is composed primarily of a few key elements. These elements make up the majority of living matter.

Major elements in living organisms:
- Carbon
- Nitrogen
- Oxygen
- Phosphorus
- Sulfur
- Hydrogen
Example: These six elements account for about 96% of the mass of living matter.

Atoms and Molecules

Atoms are the basic units of matter, and molecules are combinations of atoms held together by chemical bonds.

Atomic number: Number of protons in an atom.
Mass number: Sum of protons and neutrons in an atom.
Isotopes: Atoms of the same element with different numbers of neutrons.
Valence: The number of electrons an atom needs to gain, lose, or share to fill its outer shell.
Radioactive isotopes: Unstable isotopes that decay over time, useful in biological research and dating fossils.
Electron shells: Electrons are arranged in shells around the nucleus; the outermost shell determines chemical reactivity.
Covalent bond: A chemical bond formed when two atoms share one or more pairs of electrons.
Ionic bond: A bond formed when one atom donates an electron to another, resulting in oppositely charged ions.
Hydrogen bond: A weak bond between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom.
Van der Waals interaction: Weak attractions between molecules due to temporary partial charges.
Example: Water molecules are held together by hydrogen bonds, which give water its unique properties.

Effects of Water's Polarity

Water's molecular structure and polarity give it unique properties essential for life.

Polarity: Water is a polar molecule with a partial negative charge near the oxygen atom and a partial positive charge near the hydrogen atoms.
Cohesion: Water molecules stick together due to hydrogen bonding.
Adhesion: Water molecules can stick to other substances.
High specific heat: Water can absorb or release large amounts of heat with little change in temperature.
Ability to moderate temperature: Water stabilizes temperatures in organisms and environments.
Expansion upon freezing: Water expands as it freezes, making ice less dense than liquid water.
Versatility as a solvent: Water can dissolve many substances due to its polarity.
Example: Water dissolves salts and sugars, facilitating chemical reactions in cells.

Dissociation of Water Molecules

Water can dissociate into ions, which is important for many biological processes.

Dissociation equation:

Acids: Substances that increase the hydrogen ion concentration in a solution.
Bases: Substances that decrease the hydrogen ion concentration in a solution.
pH scale: Measures the concentration of hydrogen ions; pH below 7 is acidic, above 7 is basic.
Example: Lemon juice is acidic (low pH), while soap is basic (high pH).

Chapter 3: Carbon and the Molecular Diversity of Life

The Importance of Carbon

Carbon is the backbone of organic molecules, allowing for diversity and complexity in biological systems.

Carbon skeletons: Can vary in length, branching, and double bond position, contributing to molecular diversity.
Example: Glucose and fructose have different carbon skeleton arrangements.

Functional Groups

Functional groups are specific groups of atoms within molecules that confer particular chemical properties.

Phosphate group
Carbonyl group
Hydroxyl group
Sulfhydryl group
Methyl group
Example: The hydroxyl group (-OH) makes molecules more soluble in water.

Polymer Principles

Polymers are large molecules made by joining smaller units called monomers. They are essential for building biological macromolecules.

Condensation (dehydration) synthesis: Joins monomers by removing water.
Hydrolysis: Breaks polymers into monomers by adding water.
Example: Proteins are polymers made of amino acid monomers.

Carbohydrates: Fuel and Building Material

Carbohydrates are sugars and polymers of sugars, serving as energy sources and structural components.

Monosaccharide: Simple sugar (e.g., glucose).
Disaccharide: Two monosaccharides joined together (e.g., sucrose).
Polysaccharide: Many monosaccharides joined together (e.g., starch, cellulose).
Example: Starch is a storage polysaccharide in plants.

Lipids: Diverse Hydrophobic Molecules

Lipids are a diverse group of hydrophobic molecules that include fats, phospholipids, and steroids.

Fats: Composed of glycerol and fatty acids; used for energy storage.
Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails.
Steroids: Lipids with a four-fused ring structure; include cholesterol and hormones.
Example: Phospholipids form the bilayer of cell membranes.

Proteins: Many Structures, Many Functions

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

Amino acids: Building blocks of proteins; 20 different types.
Peptide bond: Covalent bond between amino acids formed by dehydration synthesis.
Primary structure: Sequence of amino acids in a polypeptide.
Secondary structure: Local folding patterns (e.g., alpha helix, beta sheet) stabilized by hydrogen bonds.
Tertiary structure: Overall 3D shape of a polypeptide.
Quaternary structure: Association of multiple polypeptide chains.
Example: Hemoglobin is a protein with quaternary structure, composed of four polypeptide chains.

Table: Comparison of Macromolecules

Macromolecule	Monomer	Bond Type	Function
Carbohydrate	Monosaccharide	Glycosidic bond	Energy storage, structure
Lipid	Fatty acid, glycerol	Ester bond	Energy storage, membranes
Protein	Amino acid	Peptide bond	Catalysis, structure, transport
Nucleic Acid	Nucleotide	Phosphodiester bond	Genetic information

Additional info: Academic context and definitions have been expanded for clarity and completeness. All major topics from the study guide are covered, with examples and explanations suitable for college-level General Biology students.