General Biology Exam I Study Guide: Foundations, Chemistry, and Macromolecules

Week 1: Introduction to Biology – The Science of Life

Cell Theory

The cell theory is a fundamental concept in biology that describes the properties of cells, the basic unit of life.

• All living organisms are composed of one or more cells.

• All cells arise from pre-existing cells.

Example: Humans, plants, and bacteria are all made of cells; new skin cells form from existing skin cells.

Spontaneous Generation vs. All-Cells-from-Cells Hypothesis

Historically, spontaneous generation was the belief that living organisms could arise from nonliving matter. This was disproved by scientific experimentation.

• Spontaneous generation: The idea that life can emerge from nonliving material.

• All-cells-from-cells hypothesis: States that cells only arise from other cells.

Pasteur’s Experiment: Louis Pasteur used straight-necked and swan-necked flasks to show that cells do not spontaneously appear in sterile broth unless exposed to pre-existing cells from the air.

• Straight-necked flask: Cells appeared after exposure to air.

• Swan-necked flask: No cells appeared, as airborne cells could not reach the broth.

Conclusion: Life does not spontaneously arise; cells come from other cells.

The Central Dogma of Molecular Biology

The central dogma describes the flow of genetic information within a cell.

• DNA is transcribed into RNA.

• RNA is translated into protein.

Formula:

$\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

Example: The gene for hemoglobin is encoded in DNA, transcribed to RNA, and translated to the hemoglobin protein.

Theory vs. Hypothesis

Scientific inquiry distinguishes between theories and hypotheses.

• Theory: A broad, well-supported explanation for a wide range of phenomena (e.g., cell theory).

• Hypothesis: A specific, testable prediction about what will happen under certain conditions.

Example: "All cells come from other cells" is a theory; "If broth is sterilized and isolated, no cells will appear" is a hypothesis.

Week 2: Basic Chemistry, Water, and Macromolecules

Basic Chemistry Concepts

Understanding chemical principles is essential for studying biological molecules.

• Element: Pure substance consisting of one type of atom (e.g., Oxygen).

• Compound: Substance formed from two or more elements (e.g., Water, H2O).

• Molecule: Two or more atoms bonded together (e.g., O2).

• Molecular formula: Shows the number and type of atoms (e.g., C6H12O6).

• Ionic compound: Formed by transfer of electrons (e.g., NaCl).

Atomic Structure: Atoms consist of protons, neutrons, and electrons. The atomic number equals the number of protons and identifies the element.

Chemical Bonds

Chemical bonds hold atoms together in molecules and influence molecular properties.

• Covalent bond: Atoms share electrons; can be polar (unequal sharing) or nonpolar (equal sharing).

• Hydrogen bond: Weak attraction between a hydrogen atom and an electronegative atom (e.g., O or N).

• Ionic bond: Attraction between oppositely charged ions.

• Van der Waals interactions: Weak attractions between nonpolar molecules.

• Hydrophobic interactions: Nonpolar molecules cluster together in water.

Electronegativity: Determines how electrons are shared in covalent bonds. Oxygen is more electronegative than hydrogen or carbon.

Properties of Water

Water’s unique properties are essential for life.

• Polarity: Water is a polar molecule due to electronegativity differences between O and H.

• Hydrogen bonding: Water molecules form hydrogen bonds, leading to cohesion, adhesion, high specific heat, and surface tension.

• Specific heat: Water requires a large amount of energy to change temperature.

• Ice floats: Hydrogen bonds stabilize ice, making it less dense than liquid water.

• Solvent properties: Water dissolves hydrophilic (ionic and polar) substances but not hydrophobic (nonpolar) substances.

Example: Salt (NaCl) dissolves in water; oil does not.

Week 3: Macromolecules – Carbohydrates

Monomers and Polymers

Macromolecules are large molecules made of smaller subunits.

• Monomer: Single building block (e.g., glucose).

• Polymer: Chain of monomers (e.g., starch).

• Dehydration reaction: Joins monomers by removing water.

• Hydrolysis reaction: Breaks polymers by adding water.

Formula:

$\text{Monomer}_1 + \text{Monomer}_2 \xrightarrow{\text{dehydration}} \text{Polymer} + \text{H}_2\text{O}$

$\text{Polymer} + \text{H}_2\text{O} \xrightarrow{\text{hydrolysis}} \text{Monomer}_1 + \text{Monomer}_2$

Carbohydrate Structure and Function

Carbohydrates are composed of monosaccharides and serve as energy sources and structural materials.

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

• Polysaccharides: Complex carbohydrates (e.g., starch, glycogen, cellulose, peptidoglycan).

• Glycosidic linkage: Covalent bond joining monosaccharides.

• Alpha vs. beta linkages: Determine digestibility and function (e.g., starch is digestible, cellulose is not).

Example: Starch and glycogen are storage polysaccharides; cellulose and peptidoglycan are structural.

Week 4: Macromolecules – Proteins & Nucleic Acids

Proteins: Structure and Function

Proteins are polymers of amino acids and perform diverse cellular functions.

• Amino acid: Contains an amino group, carboxyl group, and variable R group.

• Primary structure: Sequence of amino acids linked by peptide bonds.

• Secondary structure: Hydrogen bonding forms alpha helices and beta sheets.

• Tertiary structure: R-group interactions (hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic interactions).

• Quaternary structure: Association of multiple polypeptide chains.

Example: Hemoglobin has quaternary structure; sickle cell anemia results from a single amino acid change.

Nucleic Acids: DNA and RNA

Nucleic acids store and transmit genetic information.

• Nucleotide: Composed of a phosphate group, sugar (ribose or deoxyribose), and nitrogenous base.

• DNA: Double-stranded, bases are A, T, G, C; sugar is deoxyribose.

• RNA: Single-stranded, bases are A, U, G, C; sugar is ribose.

• Phosphodiester bond: Links nucleotides in a strand; forms between 3' hydroxyl and 5' phosphate.

• Base pairing: A pairs with T (DNA) or U (RNA); C pairs with G.

• Antiparallel strands: DNA strands run in opposite directions.

Formula:

$\text{DNA strand elongation: 5' \rightarrow 3'}$

Example: If one DNA strand is 5'-AATTTGGCC-3', the complementary strand is 3'-TTAAACCGG-5'.

Week 5: Macromolecules – Lipids & Membranes

Lipids and Membrane Structure

Lipids are hydrophobic molecules that form cell membranes.

• Phospholipids: Amphipathic molecules with hydrophilic heads and hydrophobic tails; form bilayers in water.

• Saturated vs. unsaturated fatty acids: Saturated tails pack tightly (less fluid); unsaturated tails have kinks (more fluid).

• Fluid mosaic model: Membrane is a dynamic structure of lipids and proteins.

Example: Cell membranes are selectively permeable; small nonpolar molecules diffuse quickly, ions and large polar molecules do not.

Membrane Transport and Osmosis

Cells regulate movement of substances across membranes.

• Passive transport: Movement down concentration gradient; includes simple diffusion and facilitated diffusion (via proteins).

• Active transport: Movement against gradient; requires energy (often ATP).

• Osmosis: Diffusion of water across a membrane; depends on solute concentration.

• Hypotonic solution: Lower solute concentration outside; water enters cell (cell swells).

• Hypertonic solution: Higher solute concentration outside; water leaves cell (cell shrinks).

• Isotonic solution: Equal solute concentration; no net water movement.

Example: Red blood cells swell in pure water (hypotonic), shrink in salty water (hypertonic).

Endocytosis and Exocytosis

Cells use vesicles to transport large particles.

• Phagocytosis: "Cell eating"; uptake of large particles (e.g., bacteria).

• Pinocytosis: "Cell drinking"; uptake of fluids.

• Receptor-mediated endocytosis: Specific uptake via receptors.

• Exocytosis: Release of substances from cell.

Appendix: Key Comparison Table

Types of Chemical Bonds

Bond Type	Strength	Example	Hydrophilic/Hydrophobic
Covalent (nonpolar)	Strong	O2, CH4	Hydrophobic
Covalent (polar)	Strong	H2O	Hydrophilic
Ionic	Strong (in dry)	NaCl	Hydrophilic
Hydrogen	Weak	Between water molecules	Hydrophilic
Van der Waals	Very weak	Between hydrocarbons	Hydrophobic

Additional info: Table inferred and expanded for clarity.