Comprehensive Study Guide: Key Concepts in College Biology

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Patterns of Evolution

Theory of Natural Selection

Natural selection is a fundamental mechanism of evolution, explaining how populations change over time. For natural selection to occur, three main conditions must be met:

Variation: Individuals in a population must vary in their traits.
Heredity: The variation must have a genetic basis and be heritable.
Selective Pressure & Differential Reproductive Success: Some variants must confer an advantage under specific environmental conditions, leading to greater reproductive success.

Examples:

Florida Beach Mouse: Variation in fur color provides camouflage; heritable genetic changes allow adaptation to sandy environments.
Lactase Persistence: Genetic variation allows some adults to digest lactose; this trait is selected in populations with dairy farming.
Sickle Cell Anemia: Heterozygotes are resistant to malaria, maintaining the allele in certain populations.
Biology of Skin Color: Variation in melanin production is an adaptation to UV exposure.

Structure and Function

Cell Types: Prokaryotes vs. Eukaryotes

Cells are the basic units of life. There are two major cell types:

Prokaryotes: Lack a nucleus and membrane-bound organelles (e.g., Bacteria and Archaea).
Eukaryotes: Have a nucleus and membrane-bound organelles (e.g., plants, animals, fungi, protists).

Similarities: Both have plasma membranes, cytoplasm, ribosomes, and genetic material.

Differences: Eukaryotes are typically larger, more complex, and compartmentalized.

Cell Compartmentalization and Organelle Function

Nucleus: Stores genetic information; site of transcription.
Mitochondria: Site of ATP production via cellular respiration.
Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids.
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
Lysosomes: Digest macromolecules and recycle cellular components.
Chloroplasts (plants): Site of photosynthesis.

If organelles are missing: The cell loses efficiency and may not survive (e.g., no mitochondria means no ATP production).

Specialized Cell Types and Organelle Abundance

Pancreatic cells: Abundant rough ER for protein (enzyme) secretion.
White blood cells: Many lysosomes for digesting pathogens.
Sperm cells: Many mitochondria for motility.
Cardiac cells: Abundant mitochondria for continuous energy.
Liver cells: Extensive smooth ER for detoxification.

Cytoskeleton: Structure and Function

Actin filaments (microfilaments): Support cell shape, enable movement, and are involved in cell division.
Microtubules: Maintain cell shape, facilitate intracellular transport, and form the mitotic spindle.

Cell Size and Surface Area-to-Volume Ratio

As cell size increases, volume grows faster than surface area, reducing efficiency of material exchange.

Formula:

where a is the length of a side of a cube-shaped cell.

Implication: Smaller cells have a higher surface area-to-volume ratio, enhancing efficiency.

Membrane Structure and Selective Permeability

Plasma membrane: Phospholipid bilayer with embedded proteins; selectively permeable.
Selective permeability: Allows some substances to cross more easily than others.

Mechanisms of Membrane Transport

Passive transport: Diffusion and facilitated diffusion (no energy required).
Active transport: Requires energy (ATP) to move substances against their gradient.
Osmosis: Diffusion of water across a membrane.
Bulk transport: Endocytosis and exocytosis for large molecules.

Transport proteins: Channel and carrier proteins facilitate movement of specific molecules.

Pathways and Transformations of Energy and Matter

ATP: Structure and Function

Adenosine triphosphate (ATP): Composed of adenine, ribose, and three phosphate groups.
Function: Main energy currency; hydrolysis of ATP releases energy for cellular work.

Photosynthesis

Location: Chloroplasts (thylakoid membranes and stroma).
Photosystems I & II: Capture light energy to drive electron transport.
Calvin Cycle: Uses ATP and NADPH to fix CO2 into carbohydrates.
Inputs: Light, water, CO2; Outputs: Glucose, O2.

Herbicide inhibition: Blocking steps in photosynthesis halts ATP/NADPH production, stopping carbohydrate synthesis.

Value to humans: Provides oxygen and food (carbohydrates).

Chemiosmosis and ATP Generation

Chemiosmosis: Movement of H+ ions across a membrane drives ATP synthesis via ATP synthase.

Cellular Respiration: Four Major Steps

Glycolysis: In cytoplasm; glucose → pyruvate; produces ATP and NADH.
Pyruvate oxidation: Pyruvate → acetyl-CoA; produces NADH and CO2.
Krebs (Citric Acid) Cycle: Acetyl-CoA → CO2; produces ATP, NADH, FADH2.
Electron Transport Chain & Chemiosmosis: In mitochondria; uses NADH/FADH2 to produce ATP and H2O.

Fermentation

Purpose: Regenerates NAD+ in absence of oxygen.
Inputs: Glucose; Outputs: Lactic acid or ethanol, ATP.

Alternate Pathways in Cellular Respiration

Fats: Broken into glycerol and fatty acids; enter glycolysis and Krebs cycle.
Proteins: Deaminated; carbon skeletons enter respiration pathways.
Weight loss/gain: Related to balance of energy intake and expenditure.

Membrane Transport in Metabolism

Cells use membrane transport to acquire substrates (e.g., CO2, O2, glucose) for photosynthesis and respiration.

Enzyme Structure and Function

Three-dimensional structure: Determined by R group interactions (hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic interactions).
Environmental factors: Temperature, pH, and inhibitors can disrupt enzyme function.

Hydrophobic vs. Hydrophilic Molecules

Hydrophobic: Nonpolar, water-repelling (e.g., lipids).
Hydrophilic: Polar, water-attracting (e.g., sugars, ions).
Relevance: Affects protein folding, membrane structure, and transport.

Enzyme Inhibitors and Feedback Inhibition

Inhibitors: Competitive (bind active site) or noncompetitive (bind elsewhere).
Feedback inhibition: End product inhibits pathway to regulate production.
Nonfunctional enzyme: Pathway is blocked; products are not made.

Information Flow, Exchange, and Storage

DNA Structure

Double helix: Two antiparallel strands of nucleotides held by hydrogen bonds between bases (A-T, G-C).

DNA Replication

Process: DNA polymerase adds nucleotides to the 3' end of a growing strand using a template.

Gene Expression: Transcription and Translation

Transcription: RNA polymerase synthesizes mRNA from DNA template; involves promoters, transcription factors, and the triplet code.
Translation: Ribosomes read mRNA; tRNA brings amino acids matching codons (anticodon interaction); synthesis proceeds 5' to 3'.

Alternative Splicing

Definition: Different combinations of exons are joined to produce multiple proteins from one gene, increasing diversity.

Regulation of Gene Expression

Chromatin remodeling: Histone acetylation (activates), deacetylation (represses), DNA methylation (represses).
Transcriptional control: Enhancers, promoters, TATA box, transcription factors.
Post-transcriptional: Alternative splicing, poly-A tail, 5' cap, RNA interference.
Post-translational: Ubiquitin tagging for protein degradation.

Mutations and Their Effects

Silent mutation: No change in protein sequence.
Nonsense mutation: Introduces a stop codon; shortens protein.
Frameshift mutation: Insertion/deletion shifts reading frame; alters downstream amino acids.
Missense mutation: Changes one amino acid; may affect function.

Sexual Life Cycle: Meiosis and Mitosis

Meiosis: Produces haploid gametes; increases genetic diversity.
Mitosis: Produces identical diploid somatic cells for growth and repair.

Haploid vs. Diploid

Haploid (n): One set of chromosomes; found in gametes after meiosis.
Diploid (2n): Two sets; found in somatic cells and after fertilization.

Steps in Meiosis and Genetic Diversity

Meiosis I: Homologous chromosomes separate (crossing over occurs).
Meiosis II: Sister chromatids separate.
Result: Four genetically unique haploid cells.

Steps in Mitosis

Prophase, Metaphase, Anaphase, Telophase: Chromosomes condense, align, separate, and decondense; results in two identical daughter cells.

Homologous Chromosomes vs. Sister Chromatids

Homologous chromosomes: Same genes, possibly different alleles; pair during meiosis.
Sister chromatids: Identical copies formed during DNA replication; separate during mitosis and meiosis II.

Gene Mutations and Cancer

p53: Tumor suppressor; loss leads to uncontrolled division.
ras: Proto-oncogene; mutation leads to constant signaling for growth.

Tumor Suppressors vs. Proto-Oncogenes

Tumor suppressors: Inhibit cell division; loss causes cancer.
Proto-oncogenes: Promote division; gain-of-function mutations cause cancer.

Role of Cytoskeleton in Cell Division

Actin: Forms contractile ring in cytokinesis.
Microtubules: Form mitotic spindle for chromosome separation.
Therapeutics: Drugs targeting microtubules (e.g., taxol) block mitosis.

Genetics: Key Terms and Patterns of Inheritance

Allele: Variant form of a gene.
Gene locus: Location of a gene on a chromosome.
Dominant/Recessive: Dominant alleles mask recessive ones.
Homozygous/Heterozygous: Same/different alleles at a locus.
Punnett square: Tool to predict offspring genotypes and phenotypes.

Patterns of Inheritance

Pleiotropy: One gene affects multiple traits (e.g., sickle cell disease).
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., AB blood type).

Scientific Techniques to Explore Molecular and Cellular Processes

DNA Analysis Techniques

Polymerase Chain Reaction (PCR): Amplifies specific DNA sequences.
Gel Electrophoresis: Separates DNA fragments by size.
Restriction Enzyme Digest: Cuts DNA at specific sequences.
DNA Profiling: Compares DNA patterns for identification.

Graphing and Data Analysis

Variables and Graph Types

Independent variable: Manipulated by the experimenter.
Dependent variable: Measured response.
Bar graph: Compares discrete categories.
Line graph: Shows trends over continuous data.

Experimental Controls and Hypotheses

Control: Standard for comparison; ensures results are due to the variable tested.
Scientific hypothesis: Testable, falsifiable statement predicting an outcome.

Additional info: Where details were not explicit, standard academic explanations were provided for completeness and clarity.