General Biology I: Study Guide 1 – Foundations of Life, Chemistry, and Biological Molecules

Introduction to Scientific Inquiry and Evolution

Scientific Method and Hypothesis Testing

The scientific method is a systematic approach used in scientific investigation. It involves making observations, forming hypotheses, conducting experiments, and drawing conclusions.

• Hypothesis: A testable statement that explains an observation or answers a scientific question.

• Theory: A well-substantiated explanation of some aspect of the natural world, based on a body of evidence.

• Observation: The act of noting and recording an event, characteristic, behavior, or anything else detected with an instrument or with the senses.

Example: Testing whether fertilizer increases plant growth by setting up controlled experiments with and without fertilizer.

Evolution and Natural Selection

Evolution is the process by which populations of organisms change over generations. Natural selection is a mechanism of evolution where individuals with advantageous traits survive and reproduce more successfully.

• Variation exists within populations.

• Some variations are heritable.

• More offspring are produced than can survive.

• Individuals with favorable traits are more likely to survive and reproduce.

Example: The development of antibiotic resistance in bacteria.

The Chemical Context of Life

Atoms, Elements, and Chemical Bonds

All matter is composed of atoms, which are the smallest units of elements. Atoms consist of protons, neutrons, and electrons. Elements are substances that cannot be broken down into simpler substances by chemical means.

• Atomic number: Number of protons in an atom.

• Mass number: Sum of protons and neutrons.

• Electron shells: Electrons are arranged in shells around the nucleus. The outermost shell determines chemical reactivity.

Types of chemical bonds:

• Covalent bonds: Atoms share electrons.

• Ionic bonds: Electrons are transferred from one atom to another, creating charged ions.

• Hydrogen bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

Example: Water molecules are held together by hydrogen bonds.

Electron Configuration and Chemical Properties

The arrangement of electrons in an atom's electron shells determines its chemical properties and reactivity. Atoms tend to fill their outermost electron shell (the octet rule).

• Valence electrons: Electrons in the outermost shell, involved in chemical bonding.

• Periodic table: Elements are organized by increasing atomic number and similar chemical properties.

Water and Life

Properties of Water

Water is essential for life due to its unique properties, which arise from its polarity and ability to form hydrogen bonds.

• High specific heat: Water can absorb a lot of heat before changing temperature.

• Cohesion and adhesion: Water molecules stick to each other (cohesion) and to other surfaces (adhesion).

• Surface tension: The surface of water is difficult to break due to hydrogen bonding.

• Ice floats: Solid water (ice) is less dense than liquid water.

• Solvent properties: Water dissolves many substances, making it a universal solvent.

Example: Water's high specific heat helps regulate Earth's climate.

Hydrogen Bonding and Molecular Interactions

Hydrogen bonds form between the slightly positive hydrogen atom of one water molecule and the slightly negative oxygen atom of another. These interactions are crucial for the structure and function of biological molecules.

Carbon and the Molecular Diversity of Life

Carbon's Versatility

Carbon atoms can form four covalent bonds, allowing for a diversity of stable organic molecules, including chains, rings, and branches.

• Functional groups: Specific groups of atoms within molecules that have characteristic properties (e.g., hydroxyl, carboxyl, amino, phosphate).

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

Example: Glucose and fructose are structural isomers.

The Structure and Function of Large Biological Molecules

Macromolecules: Carbohydrates, Lipids, Proteins, and Nucleic Acids

Living organisms are composed of four major classes of macromolecules:

• Carbohydrates: Sugars and polymers of sugars. Main functions: energy storage and structural support.

• Lipids: Fats, phospholipids, and steroids. Main functions: energy storage, membrane structure, and signaling.

• Proteins: Polymers of amino acids. Main functions: catalysis (enzymes), structure, transport, and signaling.

• Nucleic acids: DNA and RNA. Main functions: storage and transmission of genetic information.

Polymerization: Macromolecules are formed by dehydration synthesis (removal of water) and broken down by hydrolysis (addition of water).

Protein Structure and Function

Proteins have four levels of structure:

• Primary: Sequence of amino acids.

• Secondary: Local folding (alpha helices and beta sheets) stabilized by hydrogen bonds.

• Tertiary: Overall 3D shape of a polypeptide.

• Quaternary: Association of multiple polypeptide chains.

Enzymes are proteins that catalyze biochemical reactions by lowering activation energy.

Nucleic Acids: DNA and RNA

DNA (deoxyribonucleic acid) stores genetic information. RNA (ribonucleic acid) is involved in protein synthesis. DNA is double-stranded; RNA is usually single-stranded.

• Base pairing: In DNA, adenine pairs with thymine, and cytosine pairs with guanine.

• Central dogma: DNA → RNA → Protein

Acids, Bases, and pH

pH Scale and Buffers

The pH scale measures the concentration of hydrogen ions in a solution. Buffers help maintain stable pH in biological systems.

• Acid: Substance that increases H+ concentration.

• Base: Substance that decreases H+ concentration.

• Buffer: Substance that minimizes changes in pH.

Equation:

$\text{pH} = -\log_{10}[\text{H}^+]$

Summary Table: Major Classes of Biological Molecules

Class	Monomer	Function	Example
Carbohydrates	Monosaccharides	Energy, structure	Glucose, cellulose
Lipids	Fatty acids, glycerol	Energy storage, membranes	Triglycerides, phospholipids
Proteins	Amino acids	Catalysis, structure, transport	Enzymes, hemoglobin
Nucleic acids	Nucleotides	Genetic information	DNA, RNA

Additional info: Some explanations and examples were expanded for clarity and completeness, based on standard General Biology I curriculum.