Chemistry of Life: Study Guide for General Biology

Unit 1: Chemistry of Life

Overview

This unit introduces the chemical principles essential for understanding biological processes. It covers the structure and properties of atoms and molecules, types of chemical bonds, water's unique characteristics, and the major classes of biological macromolecules.

2.3–2.5: The Chemical Content of Life

2.3: Chemical Bonds

Chemical bonds are the forces that hold atoms together in molecules. Understanding these bonds is fundamental to grasping how biological molecules form and interact.

• Types of Chemical Bonds:

  • Covalent Bonds: Atoms share electron pairs. Can be nonpolar (equal sharing) or polar (unequal sharing).

  • Ionic Bonds: Electrons are transferred from one atom to another, creating charged ions that attract each other.

  • Hydrogen Bonds: Weak attractions between a hydrogen atom (covalently bonded to an electronegative atom) and another electronegative atom.

• Importance: The type of bond affects molecule stability, shape, and function in biological systems.

• Example: Water molecules are held together by polar covalent bonds, and interact via hydrogen bonds.

2.4: Chemical Reactions

Chemical reactions involve the making and breaking of chemical bonds, transforming reactants into products.

• Reactants and Products: Reactants are substances that start a reaction; products are formed as a result.

• Types of Reactions: Synthesis (building molecules), decomposition (breaking down molecules), and exchange reactions.

• Enzymes: Biological catalysts that speed up chemical reactions without being consumed.

• Example: The formation of water from hydrogen and oxygen: $2H_2 + O_2 \rightarrow 2H_2O$

2.5: Water and Life

Water's unique properties are essential for life, largely due to its ability to form hydrogen bonds.

• Cohesion and Adhesion: Cohesion is the attraction between water molecules; adhesion is the attraction between water and other substances.

• High Specific Heat: Water can absorb or release large amounts of heat with little temperature change.

• Solvent Properties: Water dissolves many substances, making it the "universal solvent" for biological reactions.

• Density of Ice: Ice is less dense than liquid water, allowing it to float and insulate aquatic environments.

• Example: Water's high heat capacity helps regulate temperature in organisms and environments.

3.1–3.6: Macromolecules and Their Functions

3.1: Carbon Compounds

Carbon's ability to form four covalent bonds makes it the backbone of organic molecules.

• Organic Molecules: Contain carbon and hydrogen; examples include carbohydrates, lipids, proteins, and nucleic acids.

• Isomers: Molecules with the same chemical formula but different structures.

• Functional Groups: Specific groups of atoms that confer particular properties (e.g., hydroxyl, carboxyl, amino, phosphate).

3.2: Macromolecules

Macromolecules are large molecules formed by joining smaller organic molecules (monomers) into polymers.

• Dehydration Synthesis: Monomers are joined by removing water.

• Hydrolysis: Polymers are broken down by adding water.

• Four Major Classes: Carbohydrates, lipids, proteins, nucleic acids.

3.3: Carbohydrates

Carbohydrates serve as fuel and building material in living organisms.

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

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

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

• Functions: Energy storage (starch, glycogen), structural support (cellulose, chitin).

• Example: Cellulose provides structural support in plant cell walls.

3.4: Lipids

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

• Fats (Triglycerides): Composed of glycerol and three fatty acids; used for energy storage.

• Saturated vs. Unsaturated Fatty Acids: Saturated have no double bonds; unsaturated have one or more double bonds.

• Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails.

• Steroids: Lipids with a carbon skeleton of four fused rings (e.g., cholesterol).

• Example: Phospholipids form the bilayer of cell membranes.

3.5: Proteins

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

• Amino Acids: 20 different types, each with a central carbon, amino group, carboxyl group, and side chain (R group).

• Peptide Bonds: Link amino acids together to form polypeptides.

• Protein Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (alpha helices, beta sheets).

  • Tertiary: Overall 3D shape.

  • Quaternary: Association of multiple polypeptides.

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

• Example: Hemoglobin transports oxygen in blood.

3.6: Nucleic Acids

Nucleic acids store and transmit hereditary information.

• DNA (Deoxyribonucleic Acid): Stores genetic information; double helix structure.

• RNA (Ribonucleic Acid): Involved in protein synthesis; usually single-stranded.

• Nucleotides: Building blocks of nucleic acids, each consisting of a sugar, phosphate group, and nitrogenous base.

• Base Pairing: In DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C).

• Example: mRNA carries genetic instructions from DNA to ribosomes for protein synthesis.

Key Vocabulary

• Matter: Anything that takes up space and has mass.

• Element: A substance that cannot be broken down by chemical means.

• Compound: A substance consisting of two or more elements in a fixed ratio.

• Atom: The smallest unit of an element, retaining its properties.

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

• Chemical Bond: Interaction between valence electrons of different atoms, holding them together in molecules.

Sample Comparison Table: Types of Chemical Bonds

Bond Type	Description	Strength	Example
Covalent	Atoms share electron pairs	Strong	H2O, O2
Ionic	Electrons transferred, forming ions	Moderate	NaCl
Hydrogen	Attraction between H and electronegative atom	Weak	Between water molecules

Additional Info

• Polarity: Molecules with uneven distribution of charge (e.g., water) are polar, affecting solubility and interactions.

• Hydrophilic vs. Hydrophobic: Hydrophilic substances interact well with water; hydrophobic substances do not.

• Biological Relevance: The structure and function of macromolecules are determined by their chemical properties and interactions.