Comprehensive Study Guide: Key Concepts in College Biology

Patterns of Evolution

Theory of Natural Selection

The theory of natural selection explains how populations evolve over time due to differences in survival and reproduction. Three essential conditions must be met for natural selection to occur:

• Variation: Individuals in a population differ in their traits.

• Heredity: These variations are genetically determined and can be passed to offspring.

• Selective Pressure & Differential Reproductive Success: Environmental factors favor certain traits, leading to higher reproductive success for individuals with those traits.

Examples of Natural Selection

• Florida Beach Mouse: Variation in fur color provides camouflage; genetic inheritance ensures offspring resemble parents; predation acts as selective pressure.

• Lactase Persistence: Genetic variation allows some adults to digest lactose; inherited trait; dietary habits and survival act as selective pressure.

• Sickle Cell Anemia: Variation in hemoglobin gene; inherited; malaria acts as selective pressure, favoring heterozygotes in certain regions.

• Biology of Skin Color: Variation in melanin production; inherited; UV exposure and vitamin D synthesis act as selective pressures.

Structure and Function

Cell Types: Prokaryotes vs. Eukaryotes

Cells are the basic unit of life. Their structure determines their function. Two major cell types:

• Prokaryotes: Lack membrane-bound organelles; DNA in nucleoid; smaller size; e.g., bacteria.

• Eukaryotes: Have membrane-bound organelles (nucleus, mitochondria, etc.); DNA in nucleus; larger size; e.g., plants, animals.

Cell Compartmentalization

• Organelles: Specialized structures (e.g., mitochondria, ER, Golgi) increase efficiency by compartmentalizing functions.

• Missing Organelles: Loss of organelles impairs cell function (e.g., no mitochondria = no ATP production).

Specialized Cell Types

• Pancreatic Cells: Abundant ER and Golgi for protein secretion (insulin).

• White Blood Cells: Lysosomes for digestion of pathogens.

• Sperm Cells: Mitochondria for energy; flagellum for movement.

• Cardiac Cells: Mitochondria for continuous energy; gap junctions for communication.

• Liver Cells: Smooth ER for detoxification; mitochondria for metabolism.

Cytoskeleton

• Actin Filaments: Provide structure, enable movement.

• Microtubules: Organize cell shape, transport vesicles, form spindle during cell division.

Cell Size and Surface Area to Volume Ratio

• As cell size increases, surface area to volume ratio decreases.

• Lower ratio limits efficiency of transport and metabolism.

Membrane Structure and Selective Permeability

• Plasma Membrane: Phospholipid bilayer with embedded proteins.

• Selective Permeability: Allows certain molecules to pass while blocking others.

Mechanisms of Membrane Transport

• Passive Transport: Diffusion, osmosis; no energy required.

• Facilitated Diffusion: Uses channel/carrier proteins.

• Active Transport: Requires energy (ATP); moves substances against gradient.

• Bulk Transport: Endocytosis/exocytosis for large molecules.

Transport Type	Energy Required	Proteins Used	Molecules Transported
Passive	No	None	Small, nonpolar
Facilitated	No	Channel/Carrier	Polar, ions
Active	Yes	Pumps	Ions, large molecules
Bulk	Yes	Vesicles	Macromolecules

Pathways and Transformations of Energy and Matter

ATP: Structure and Function

ATP (adenosine triphosphate) is the primary energy currency of the cell.

• Structure: Adenine, ribose, three phosphate groups.

• Energy released by hydrolysis of terminal phosphate bond.

$\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

Photosynthesis

• Chloroplasts: Site of photosynthesis; contain thylakoids and stroma.

• Photosystems I & II: Located in thylakoid membrane; capture light energy.

• Calvin Cycle: Occurs in stroma; uses ATP and NADPH to fix CO2 into carbohydrates.

• Inputs: Light, water, CO2

• Outputs: Glucose, O2

Herbicide Inhibition

• Blocking steps in photosynthesis reduces ATP and carbohydrate production, affecting plant growth.

Value of Photosynthesis

• Provides oxygen and food for humans.

Chemiosmosis and ATP Generation

• Movement of H+ across membrane creates gradient.

• ATP synthase uses gradient to produce ATP.

$\text{ADP} + \text{P}_i \xrightarrow{\text{ATP synthase}} \text{ATP}$

Cellular Respiration

• Step 1: Glycolysis (cytoplasm): Glucose → pyruvate; produces ATP, NADH.

• Step 2: Pyruvate Oxidation (mitochondria): Pyruvate → Acetyl-CoA; produces NADH, CO2.

• Step 3: Citric Acid Cycle (mitochondria): Acetyl-CoA → CO2; produces ATP, NADH, FADH2.

• Step 4: Electron Transport Chain (mitochondria): NADH/FADH2 → ATP, H2O.

Fermentation

• Occurs without oxygen; converts pyruvate to lactic acid or ethanol; regenerates NAD+.

Alternate Pathways

• Fats and proteins can enter cellular respiration at different steps to produce ATP.

• Weight loss: More substrate used for ATP production; weight gain: excess substrate stored.

Membrane Transport in Energy Acquisition

• Transport proteins acquire molecules for photosynthesis and respiration.

Enzyme Structure and Function

• Three-dimensional structure determined by R group interactions (hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bridges).

• Environmental factors (pH, temperature) can disrupt structure and function.

Hydrophobic vs. Hydrophilic Molecules

• Hydrophobic: Nonpolar, repel water; important in membrane structure.

• Hydrophilic: Polar, attract water; important in protein structure and transport.

Enzyme Inhibition

• Inhibitors block enzyme activity; feedback inhibition regulates pathways.

• If enzyme fails, pathway products are not produced.

Information Flow, Exchange, and Storage

DNA Structure

• Double helix; two strands of nucleotides held by hydrogen bonds.

DNA Replication

• DNA polymerase adds nucleotides to growing strand; semi-conservative process.

Transcription and Translation

• Transcription: DNA → mRNA; RNA polymerase, transcription factors, promoters, TATA box.

• Translation: mRNA → protein; ribosome, start codon, triplet code, anticodon, 5’ to 3’ direction.

Alternative Splicing

• Allows one gene to code for multiple proteins; increases diversity.

Regulation of Gene Expression

• Chromatin Remodeling: Histone acetylation (activates), deacetylation (represses), DNA methylation (represses).

• Transcription: Enhancers, promoters, TATA box, transcription factors.

• Post-transcription: Alternative splicing, poly A tail, 5’ cap, RNA interference.

• Post-translation: Ubiquitin tag marks proteins for degradation.

Mutations

• Silent: No change in protein.

• Nonsense: Premature stop codon; truncated protein.

• Frameshift: Insertion/deletion shifts reading frame; altered protein.

• Missense: Changes one amino acid; may affect function.

Sexual Life Cycle: Meiosis and Mitosis

• Meiosis produces gametes (haploid); mitosis produces somatic cells (diploid).

• Alternation between meiosis and mitosis ensures genetic diversity and growth.

Haploid vs. Diploid

• Haploid: One set of chromosomes (gametes).

• Diploid: Two sets (somatic cells).

Steps in Meiosis

• Meiosis I: Homologous chromosomes separate.

• Meiosis II: Sister chromatids separate.

• Leads to genetic diversity via crossing over and independent assortment.

Steps in Mitosis

• Prophase, metaphase, anaphase, telophase; produces two identical daughter cells.

Homologous Chromosomes vs. Sister Chromatids

• Homologous: Same genes, different alleles.

• Sister chromatids: Identical copies.

Gene Mutations and Cancer

• Mutations in p53 (tumor suppressor) or ras (proto-oncogene) disrupt cell cycle, leading to cancer.

• Tumor suppressors inhibit cell division; proto-oncogenes promote it.

Role of Cytoskeleton in Cell Division

• Actin and microtubules form spindle and contractile ring; targeted in cancer therapy.

• Affect mitosis and cytokinesis steps.

Genetics: Chromosomes and Inheritance

• Allele: Variant of a gene.

• Gene locus: Location on chromosome.

• Dominant/Recessive: Dominant masks recessive.

• Homozygous: Same alleles.

• Heterozygous: Different alleles.

• Punnett Square: Diagram to predict offspring genotypes.

Patterns of Inheritance

• Pleiotropy: One gene affects multiple traits (e.g., sickle cell anemia).

• Polygenic Inheritance: Multiple genes affect one trait (e.g., skin color).

• Sex Linkage: Genes on sex chromosomes (e.g., hemophilia).

• Codominance: Both alleles expressed (e.g., blood type AB).

Scientific Techniques to Explore Molecular and Cellular Processes

DNA Study Techniques

• Polymerase Chain Reaction (PCR): Amplifies DNA.

• Gel Electrophoresis: Separates DNA fragments by size.

• Restriction Enzyme Digest: Cuts DNA at specific sequences.

• DNA Profiles: Compare genetic material for identification.

Graphing and Data Analysis

Variables

• Independent Variable: Manipulated by experimenter.

• Dependent Variable: Measured outcome.

Types of Graphs

• Bar Graph: Compares discrete categories.

• Line Graph: Shows trends over time or continuous data.

Controls and Hypotheses

• Control: Standard for comparison; ensures validity.

• Scientific Hypothesis: Testable statement predicting outcome.

Example: In an experiment testing fertilizer effects, the control group receives no fertilizer, the independent variable is fertilizer amount, and the dependent variable is plant growth.