Comprehensive Study Guide: Key Concepts in College Biology

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

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, several conditions must be met:

Variation: Individuals in a population must vary in their traits.
Heredity: These variations must have a genetic basis and be heritable.
Selective Pressure & Differential Reproductive Success: Environmental factors favor certain traits, leading to increased survival and reproduction of individuals with those traits.

Examples:

Florida Beach Mouse: Variation in fur color provides camouflage; heritable through genes; selective pressure from predators leads to differential survival.
Evolution of Lactase Persistence: Some human populations retain the ability to digest lactose into adulthood due to genetic variation; this trait is advantageous where dairy is a dietary staple.
Sickle Cell Anemia: The sickle cell allele provides malaria resistance in heterozygotes, demonstrating how selective pressures can maintain genetic variation.
The Biology of Skin Color: Variation in skin pigmentation is influenced by environmental UV exposure and is heritable, affecting vitamin D synthesis and folate protection.

Structure and Function

Cell Types: Prokaryotes vs. Eukaryotes

Cells are the basic units of life, and their structure determines their function. There are two major cell types:

Prokaryotes: Lack a nucleus and membrane-bound organelles; DNA is in the nucleoid region (e.g., Bacteria and Archaea).
Eukaryotes: Have a nucleus and membrane-bound organelles (e.g., Animals, Plants, Fungi, Protists).

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

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

Cell Compartmentalization and Organelles

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 and detoxifies.
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, cellular processes are disrupted, leading to cell dysfunction or death.

Specialized Cell Types and Organelle Abundance

Pancreatic Cells: Abundant rough ER for protein (enzyme/hormone) secretion.
White Blood Cells: Many lysosomes for digesting pathogens.
Sperm Cells: Many mitochondria for motility.
Cardiac Cells: Abundant mitochondria for continuous energy supply.
Liver Cells: Extensive smooth ER for detoxification and metabolism.

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 during cell division.

Cell Size and Surface Area-to-Volume Ratio

As cell size increases, volume grows faster than surface area, reducing the surface area-to-volume ratio. This limits efficient exchange of materials, affecting cell function.

Formula:

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

Membrane Structure and Selective Permeability

Plasma Membrane: Composed of a phospholipid bilayer with embedded proteins; selectively permeable.
Selective Permeability: Allows some substances to cross more easily than others, maintaining homeostasis.

Mechanisms of Membrane Transport

Passive Transport: No energy required; includes simple diffusion, facilitated diffusion (via channel/carrier proteins), and osmosis (water movement).
Active Transport: Requires energy (ATP); moves substances against their concentration gradient (e.g., sodium-potassium pump).
Bulk Transport: Endocytosis and exocytosis for large molecules.

Factors Determining Transport: Molecule size, polarity, charge, and concentration gradient.

Pathways and Transformations of Energy and Matter

ATP: Structure and Function

Adenosine Triphosphate (ATP): Composed of adenine, ribose, and three phosphate groups.
Function: Major 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: Occurs in the stroma; uses ATP and NADPH to fix CO2 into carbohydrates.
Inputs: Light, water, CO2; Outputs: O2, glucose.

If steps are inhibited (e.g., by herbicides), photosynthesis and energy production are disrupted, affecting plant survival.

Value to Humans: Provides oxygen and food (glucose); basis of most food chains.

Chemiosmosis and ATP Generation

Chemiosmosis: Movement of protons down their gradient through ATP synthase, generating ATP in both mitochondria (cellular respiration) and chloroplasts (photosynthesis).

Cellular Respiration: Four Major Steps

Glycolysis: In cytoplasm; glucose → 2 pyruvate, 2 ATP, 2 NADH.
Pyruvate Oxidation: In mitochondria; pyruvate → acetyl-CoA, NADH, CO2.
Krebs Cycle (Citric Acid Cycle): Acetyl-CoA → CO2, NADH, FADH2, ATP.
Electron Transport Chain & Chemiosmosis: NADH/FADH2 donate electrons; O2 is final electron acceptor; ATP produced.

Fermentation

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

Alternate Pathways for ATP Production

Fats: Broken into fatty acids, enter Krebs cycle as acetyl-CoA.
Proteins: Deaminated, enter as intermediates in glycolysis or Krebs cycle.

Weight loss occurs when more energy is expended than consumed; weight gain is the reverse.

Membrane Transport in Metabolism

Cells use membrane transport to acquire glucose, O2, and other molecules 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, repel water (e.g., lipids).
Hydrophilic: Polar, interact with water (e.g., sugars, ions).

This affects protein folding, membrane structure, and molecular interactions.

Enzyme Inhibition and Feedback

Inhibitors: Competitive (bind active site) or noncompetitive (bind elsewhere).
Feedback Inhibition: End product inhibits pathway, regulating metabolic flux.

If an enzyme fails, pathway products decrease or accumulate abnormally.

Information Flow, Exchange, and Storage

DNA Structure

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

DNA Replication

Process: DNA polymerase adds nucleotides to the 3' end of a growing strand, using the original strand as 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 anticodons match codons, adding amino acids to the growing polypeptide.

Alternative Splicing

Allows a single gene to code for multiple proteins, increasing organismal 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 Control: Alternative splicing, poly-A tail, 5' cap, RNA interference.
Post-Translational Control: Ubiquitin tagging for protein degradation.

Mutations and Their Effects

Silent Mutation: No change in protein sequence.
Nonsense Mutation: Introduces a stop codon, truncating the protein.
Frameshift Mutation: Insertion/deletion shifts reading frame, altering downstream amino acids.
Missense Mutation: Changes one amino acid in the protein.

Sexual Life Cycle: Meiosis and Mitosis

Meiosis: Produces haploid gametes; increases genetic diversity via crossing over and independent assortment.
Mitosis: Produces two 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 of chromosomes; found in somatic cells and after fertilization.

Steps in Meiosis and Mitosis

Meiosis: Two divisions (Meiosis I and II); leads to four genetically unique haploid cells.
Mitosis: One division; leads to two identical diploid cells.

Homologous Chromosomes vs. Sister Chromatids

Homologous Chromosomes: Same genes, possibly different alleles; one from each parent.
Sister Chromatids: Identical copies formed during DNA replication.

Gene Mutations and Cancer

p53: Tumor suppressor; loss leads to uncontrolled cell division.
ras: Proto-oncogene; mutation can cause constant cell division signals.

Tumor Suppressors vs. Proto-Oncogenes

Tumor Suppressors: Inhibit cell division; loss of function can cause cancer.
Proto-Oncogenes: Promote cell division; gain of function mutations can cause cancer.

Role of Cytoskeleton in Cell Division

Actin: Forms contractile ring in cytokinesis.
Microtubules: Form mitotic spindle for chromosome segregation.

Targeted by cancer therapeutics (e.g., taxol inhibits microtubule disassembly).

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 in heterozygotes.
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 anemia).
Polygenic Inheritance: Multiple genes affect one trait (e.g., skin color).
Sex Linkage: Genes on sex chromosomes (e.g., color blindness).
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 using an electric field.
Restriction Enzyme Digest: Cuts DNA at specific sequences.
DNA Profiling: Compares DNA samples for identification (e.g., forensic analysis).

Graphing and Data Analysis

Variables and Graph Types

Independent Variable: Manipulated by the experimenter.
Dependent Variable: Measured outcome.
Bar Graphs: Compare discrete categories.
Line Graphs: Show trends over continuous data (e.g., time).

Experimental Controls and Hypotheses

Control: Standard for comparison; ensures observed effects are due to the independent variable.
Scientific Hypothesis: Testable, falsifiable statement predicting an outcome based on prior knowledge.