General Biology: Core Concepts and Processes

Biological Molecules and Chemical Foundations

Water and Carbon: The Chemical Basis of Life

Life depends on the unique properties of water and carbon-based molecules. These molecules form the foundation for biological structure and function.

• Water is a polar molecule, allowing for hydrogen bonding, high specific heat, and solvent properties.

• Carbon forms four covalent bonds, enabling the diversity of organic molecules.

• Functional groups (e.g., hydroxyl, carboxyl, amino, phosphate) confer specific chemical properties to organic molecules.

Macromolecules: Structure and Function

• Carbohydrates: Built from monosaccharides (simple sugars) via condensation reactions (dehydration synthesis). Serve as energy storage (e.g., starch, glycogen) and structural components (e.g., cellulose, chitin).

• Proteins: Polymers of amino acids linked by peptide bonds. Structure determines function (primary, secondary, tertiary, quaternary levels). Functions include catalysis (enzymes), structure, transport, and signaling.

• Nucleic Acids: Polymers of nucleotides (DNA and RNA). Store and transmit genetic information. DNA is double-stranded; RNA is usually single-stranded.

• Lipids: Hydrophobic molecules including fats, phospholipids, and steroids. Important for energy storage, membrane structure, and signaling.

Cell Structure and Function

Cell Theory and Types of Cells

All living organisms are composed of cells, which are the basic units of life. Cells can be classified as prokaryotic or eukaryotic.

• Prokaryotes: Lack a nucleus; DNA is in the nucleoid region. Examples: Bacteria and Archaea.

• Eukaryotes: Have a nucleus and membrane-bound organelles. Examples: Plants, animals, fungi, protists.

Cell Membranes and Transport

• Phospholipid bilayer forms the basic structure of cell membranes.

• Membranes are selectively permeable, allowing some substances to cross more easily than others.

• Transport mechanisms include passive transport (diffusion, osmosis, facilitated diffusion) and active transport (requires energy, e.g., pumps).

Energy, Enzymes, and Metabolism

Thermodynamics and Metabolic Pathways

Cells transform energy through metabolic pathways, governed by the laws of thermodynamics.

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

• Second Law of Thermodynamics: Entropy (disorder) increases in spontaneous reactions.

• Enzymes: Biological catalysts that lower activation energy and increase reaction rates.

Equation:

$\Delta G = \Delta H - T\Delta S$

Where $\Delta G$ is the change in free energy, $\Delta H$ is the change in enthalpy, $T$ is temperature, and $\Delta S$ is the change in entropy.

Cellular Respiration and Fermentation

Overview of Cellular Respiration

Cellular respiration is the process by which cells extract energy from glucose and other organic molecules.

• Glycolysis: Occurs in the cytoplasm; glucose is split into two pyruvate molecules, producing ATP and NADH.

• Pyruvate Processing: Pyruvate is converted to acetyl-CoA, releasing CO2 and generating NADH.

• Citric Acid Cycle (Krebs Cycle): Acetyl-CoA is oxidized to CO2; produces ATP, NADH, and FADH2.

• Electron Transport Chain (ETC): Electrons from NADH and FADH2 are transferred through protein complexes, driving ATP synthesis via oxidative phosphorylation.

Equation:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{energy (ATP)}$

Fermentation

• Occurs when oxygen is not available.

• Regenerates NAD+ by reducing pyruvate to lactate or ethanol.

Photosynthesis

Light-Dependent and Light-Independent Reactions

Photosynthesis converts light energy into chemical energy in plants, algae, and some bacteria.

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

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

Equation:

$6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

Cell Cycle, Mitosis, and Meiosis

Cell Cycle and Regulation

• The cell cycle consists of interphase (G1, S, G2) and mitotic phase (mitosis and cytokinesis).

• Regulated by cyclins and cyclin-dependent kinases (CDKs).

Mitosis

• Produces two genetically identical diploid daughter cells.

• Stages: prophase, metaphase, anaphase, telophase, cytokinesis.

Meiosis

• Produces four genetically unique haploid gametes.

• Involves two divisions: meiosis I and meiosis II.

• Promotes genetic diversity through crossing over and independent assortment.

Mendelian Genetics and Inheritance

Mendel's Laws

• Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.

• Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

Patterns of Inheritance

• Dominant and recessive alleles: Dominant alleles mask recessive ones in heterozygotes.

• Incomplete dominance: Heterozygotes show intermediate phenotype.

• Codominance: Both alleles are expressed equally.

• Sex-linked inheritance: Genes located on sex chromosomes show unique inheritance patterns.

DNA, Genes, and Gene Expression

DNA Structure and Replication

• DNA is a double helix composed of nucleotides (A, T, C, G).

• Replication is semi-conservative; each new DNA molecule has one old and one new strand.

Transcription and Translation

• Transcription: DNA is transcribed into messenger RNA (mRNA).

• RNA processing: In eukaryotes, includes splicing, 5' capping, and 3' polyadenylation.

• Translation: mRNA is translated into protein at the ribosome.

Gene Regulation

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

• Eukaryotes: Regulation occurs at multiple levels (chromatin structure, transcription, RNA processing, translation).

Evolution and Phylogeny

Principles of Evolution

• Evolution is the change in allele frequencies in a population over time.

• Mechanisms include natural selection, genetic drift, gene flow, and mutation.

Phylogenetic Trees

• Phylogenies depict evolutionary relationships among species.

• Constructed using morphological and molecular data.

Additional Topics

• Epigenetics: Heritable changes in gene expression not due to changes in DNA sequence (e.g., DNA methylation, histone modification).

• Viruses: Non-cellular infectious agents; replicate only inside host cells.

Sample Table: Comparison of Cell Types

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	No	Yes
Membrane-bound organelles	No	Yes
Size	Small (1-10 μm)	Larger (10-100 μm)
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Additional info: Some details and diagrams were inferred or expanded for clarity and completeness based on standard General Biology curriculum.