Lecture Notes: AP Biology Unit 4 Review

Introduction

• Instructor: Mr. W (Glenn Wolkenfeld), retired AP Biology teacher.
• Focus: Prepare for AP Bio exams by interacting with materials and getting feedback.
• Resources: LearnDashBiology.com, BioMania AP Bio App, Student-friendly guide.

Unit 4: Cell Communication and Cell Cycle

Part 1: Cell Signaling

• Importance of Cell Communication:
  • Essential for cell populations and multicellular organisms.
  • Types: Direct cell-to-cell communication, long-distance (hormones), short-distance (local regulators).
• Ligands:
  • Signaling molecules that bind to receptors based on complementary shapes.
  • Types: Hormones, local regulators.
• Quorum Sensing:
  • Cell communication in bacteria leading to biofilm formation.
• Phases of Cell Signaling:
  • Reception, Signal transduction, Cellular Response.
• Steroid vs. Water-soluble Hormones:
  • Steroid: Non-polar, diffuse through membranes, affect gene expression.
  • Water-soluble: Bind to surface receptors, act via second messengers.

Part 2: Epinephrine and G-Protein Coupled Receptor Systems

• Epinephrine (Adrenaline) and the Fight-or-Flight Response:
  • Effect on liver cells: Breaks down glycogen to glucose.
  • Binds to G-protein coupled receptors, initiates signaling cascade.
• Mechanism:
  • Inactive State: G-protein coupled receptor and adenyl cyclase inactive.
  • Activation: Epinephrine binds, G-protein becomes active (binds GTP), activates adenyl cyclase.
  • Signal Amplification: Cascade of kinase activations leading to cellular responses.

Part 3: Feedback and Homeostasis

Homeostasis

• Tendency to maintain internal conditions at optimal levels.
• Example: Body temperature regulation.

Feedback Mechanisms

• Negative Feedback:
  • Set points and regulation (e.g., thermostat analogy).
  • Paired antagonistic systems (e.g., insulin and glucagon in blood sugar regulation).
• Positive Feedback:
  • Drives processes to completion (e.g., childbirth, fruit ripening).

Part 4: Cell Cycle

Overview of Mitosis

• Functions: Growth, repair, and reproduction in unicellular organisms.

Phases of the Cell Cycle

• Interphase: G1 (Growth), S (DNA Synthesis), G2 (Preparation for mitosis).
• M Phase: Mitosis and cytokinesis.

Phases of Mitosis

• Prophase: Chromosomes condense, spindle formation.
• Metaphase: Chromosomes align at the equator.
• Anaphase: Sister chromatids separate.
• Telophase: Nuclear membranes reform.
• Cytokinesis: Cellular division.

Part 5: Regulation of the Cell Cycle

Checkpoints

• Purpose: Assess conditions before progression.
• Key Checkpoints: G1, G2, M.

Apoptosis

• Programmed Cell Death: Regulated, prevents damage from cell debris.

Cyclins and Cyclin-Dependent Kinases

• Cyclins: Concentration changes throughout the cycle.
• CDKs: Activate cell cycle progression.

Cancer

• Causes: Mutations in proto-oncogenes and tumor suppressor genes.
• Proto-oncogenes: Lead to excessive growth factor production.
• Tumor Suppressors (e.g., p53): Loss of function leads to unregulated cell division.

Ras Proto-oncogene

• Normal Function: Activated by ligands, regulates cell division.
• Cancerous Mutation: Constitutive activation without ligand leads to excessive growth.

P53 Tumor Suppressor

• Function: Halts cycle for DNA repair or initiates apoptosis if damage is irreparable.
• Mutation: Loss of function leads to division with damaged DNA.

Conclusion

• Resources: Interactive tutorials and reviews at LearnBiology.com.
• Guarantee a 4 or 5 on the AP Bio exam by using available resources.