General Biology I: Key Concepts and Review Guide

Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells lack a nucleus and membrane-bound organelles; examples include Bacteria and Archaea.

• Eukaryotic cells have a true nucleus and various organelles; examples include Plants, Animals, Fungi, and Protists.

• Key differences: DNA location, organelle presence, cell size, and complexity.

Cell Organelles

• Nucleus: Contains genetic material (DNA).

• Mitochondria: Site of cellular respiration and ATP production.

• Chloroplasts: Site of photosynthesis in plant cells.

• Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; Smooth ER synthesizes lipids.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes for waste breakdown.

Chemical Basis of Life

Bonds, Water, and Macromolecules

• Covalent bonds: Atoms share electrons; strong and stable.

• Hydrogen bonds: Weak attractions between polar molecules, important in water and biological molecules.

• Ionic bonds: Transfer of electrons from one atom to another, forming charged ions.

• Water: Polar molecule, excellent solvent, high specific heat, cohesion, and adhesion properties.

• pH: Measures hydrogen ion concentration; acidic (pH < 7), basic (pH > 7), neutral (pH = 7).

Macromolecules

Carbohydrates

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

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

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

• Functions: Energy storage, structural support.

Lipids

• Fats (triglycerides): Glycerol + 3 fatty acids; energy storage.

• Phospholipids: Glycerol + 2 fatty acids + phosphate; major component of cell membranes.

• Steroids: Four fused rings; hormones and membrane components.

• Amphipathic: Molecules with both hydrophilic and hydrophobic regions (e.g., phospholipids).

Proteins

• Amino acids: Building blocks of proteins; 20 standard types.

• Levels of structure: Primary (sequence), secondary (α-helix, β-sheet), tertiary (3D folding), quaternary (multiple polypeptides).

• Functions: Enzymes, structure, transport, signaling, defense.

Nucleic Acids

• DNA: Stores genetic information; double helix structure.

• RNA: Involved in protein synthesis; single-stranded.

• Nucleotides: Monomers of nucleic acids; consist of a sugar, phosphate, and nitrogenous base.

Cell Membranes and Transport

Membrane Structure

• Phospholipid bilayer: Hydrophilic heads face outward, hydrophobic tails inward.

• Fluid mosaic model: Membrane is flexible with proteins embedded or attached.

Transport Mechanisms

• Passive transport: Diffusion, facilitated diffusion (no energy required).

• Active transport: Requires energy (ATP) to move substances against concentration gradients.

• Osmosis: Diffusion of water across a selectively permeable membrane.

Energy, Enzymes, and Metabolism

Thermodynamics

• First Law: Energy cannot be created or destroyed, only transformed.

• Second Law: Entropy (disorder) increases in spontaneous processes.

Enzymes

• Catalysts: Speed up reactions by lowering activation energy.

• Active site: Region where substrate binds.

• Induced fit: Enzyme changes shape to fit substrate.

• Factors affecting activity: Temperature, pH, inhibitors, and activators.

Cellular Respiration and Fermentation

Overview

• Purpose: Convert glucose to ATP, the cell's energy currency.

• Equation: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP)}$

Stages

• Glycolysis: Occurs in cytoplasm; splits glucose into 2 pyruvate, produces 2 ATP and 2 NADH.

• Krebs Cycle (Citric Acid Cycle): In mitochondria; completes glucose breakdown, produces NADH, FADH2, ATP, CO2.

• Electron Transport Chain (ETC): Uses NADH and FADH2 to generate ATP via oxidative phosphorylation.

• Fermentation: Anaerobic process; regenerates NAD+, produces lactic acid or ethanol.

Photosynthesis

Overview

• Purpose: Convert light energy to chemical energy (glucose).

• Equation: $6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$

Stages

• Light-dependent reactions: Occur in thylakoid membranes; produce ATP and NADPH.

• Calvin Cycle (light-independent reactions): Occur in stroma; use ATP and NADPH to fix CO2 into glucose.

Cell Communication and Signaling

Endocytosis and Exocytosis

• Endocytosis: Uptake of materials into the cell via vesicles.

• Exocytosis: Export of materials out of the cell via vesicles.

Cell Signaling

• Signal transduction: Process by which a cell responds to external signals via receptors and secondary messengers.

• Receptors: Proteins that bind signaling molecules (ligands) and initiate cellular responses.

Genetics

Mendelian Genetics

• Gene: Unit of heredity; codes for a protein.

• Allele: Different forms of a gene.

• Genotype: Genetic makeup; Phenotype: Observable traits.

• Dominant vs. Recessive: Dominant alleles mask recessive ones in heterozygotes.

• Monohybrid cross: Involves one gene; Dihybrid cross: Involves two genes.

Non-Mendelian Genetics

• Incomplete dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles expressed equally.

• Sex-linked traits: Genes located on sex chromosomes (e.g., X-linked traits).

DNA Structure, Replication, and Expression

DNA Replication

• Semi-conservative: Each new DNA molecule has one old and one new strand.

• Key enzymes: DNA polymerase, helicase, primase, ligase.

Transcription and Translation

• Transcription: DNA is copied into mRNA.

• Translation: mRNA is decoded to build a protein at the ribosome.

• tRNA: Brings amino acids to ribosome; rRNA: Structural and catalytic component of ribosome.

Gene Regulation

• Prokaryotes: Operons (e.g., lac operon) regulate gene expression.

• Eukaryotes: Regulation at transcriptional, post-transcriptional, translational, and post-translational levels.

Mutation and DNA Repair

• Mutation: Change in DNA sequence; can be spontaneous or induced.

• DNA repair mechanisms: Proofreading, mismatch repair, excision repair.

• Gene therapy: Techniques to correct defective genes.

Summary Table: Key Macromolecules

Macromolecule	Monomer	Bond Type	Main Functions
Carbohydrates	Monosaccharides	Glycosidic linkage	Energy, structure
Lipids	Fatty acids, glycerol	Ester bond	Energy storage, membranes
Proteins	Amino acids	Peptide bond	Catalysis, structure, transport
Nucleic Acids	Nucleotides	Phosphodiester bond	Genetic information

Additional info:

• Some explanations and definitions were expanded for clarity and completeness.

• Table summarizes main macromolecules for quick review.