Lecture Notes: AP Biology Review - Unit 4

Introduction

• Focus on preparing for AP Bio Exam or Unit 4 Test.
• Topics covered:
  1. Cell Communication
  2. Feedback and Homeostasis
  3. Cell Division and Cell Cycle
  4. Cell Cycle Regulation, Cancer, and Apoptosis

Part 1: Cell Communication

Overview

• Cells constantly communicate; they do not operate in isolation.
• Direct Cell-to-Cell Communication: Molecules pass through junctions between adjacent cells.
• Signal-Based Communication:
  • Ligands: Signaling molecules split into hormones (long distance) and local regulators (short distance).

Ligands and Their Function

• Hormones travel through the bloodstream, whereas local regulators act over short distances.
• Binding of ligands to receptors is based on complementary shapes.

Quorum Sensing in Bacteria

• Bacteria release signaling molecules that activate genes to produce biofilms as a form of communication.

Phases of Cell Signaling

1. Reception: Ligand binds to a receptor molecule.
2. Transduction: Signal transformed and amplified.
3. Response: Activation of cellular processes.

Hormones and Their Mechanisms

• Water-Soluble Hormones: Bind to receptors and utilize second messengers.
• Steroid Hormones: Diffuse through membranes, bind cytoplasmic receptors, and activate genes.

Epinephrine and G-Protein Coupled Receptors

• Fight or Flight Response: Epinephrine affects various body systems, including liver, to produce glucose.
• G Protein Mechanism:
  • Activation of adenylate cyclase, conversion of ATP to cyclic AMP (second messenger).
  • Amplification through phosphorylation cascades.

Part 2: Feedback and Homeostasis

Homeostasis and Feedback Mechanisms

• Homeostasis: Maintaining internal conditions.
• Negative Feedback: Mechanism that maintains homeostasis (e.g., temperature regulation).
• Positive Feedback: Accelerates processes to conclusion (e.g., childbirth).

Blood Sugar Regulation

• Insulin: Released when blood glucose is high, promoting storage as glycogen.
• Glucagon: Released when blood glucose is low, promoting conversion of glycogen to glucose.
• Diabetes Disruption:
  • Type 1: Autoimmune attack on insulin-producing cells.
  • Type 2: Insulin resistance.

Part 3: The Cell Cycle

Overview

• Mitosis: Duplicates chromosomes, leading to two daughter cells.
• Interphase: Divided into G1 (growth), S (synthesis), and G2 (preparation for mitosis).
• Mphase: Mitosis and cytokinesis occur.

Phases of Mitosis

1. Prophase: Chromosomes condense, nuclear membrane disintegrates.
2. Metaphase: Chromosomes line up at the equator.
3. Anaphase: Sister chromatids pulled apart.
4. Telophase: Nuclear membranes form around chromosomes.
5. Cytokinesis: Cytoplasm divides, forming two cells.

G0 Phase

• Highly specialized cells exit the cycle and do not divide.

Part 4: Regulation and Cancer

Checkpoints and Apoptosis

• Checkpoints: Ensure cell cycle progression only under correct conditions.
• Apoptosis: Programmed cell death for damaged cells.

Cyclins and CDKs

• Cyclins: Regulate progression in cell cycle, concentration varies.
• CDKs: Cyclin-dependent kinases, activate cell cycle processes.

Cancer and Genetic Mutations

• Proto-oncogenes: Mutations here increase cell division.
• Tumor Suppressors: Mutations remove division inhibitors.

Ras and p53 Mutations

• Ras Protein: Normally activates upon ligand binding; mutations lead to constant activation and cell division.
• p53: Tumor suppressor; mutation leads to division without DNA repair, increasing cancer risk.

Conclusion

• Encouragement for further study and understanding through resources like learn-biology.com.