Cell Structure, Membrane Transport, and Cell Division: Study Notes for Anatomy & Physiology

Chapter 3: Cell Structure and Function

Cell Theory and Basic Concepts

The cell theory is a fundamental principle in biology that describes the properties and significance of cells in living organisms.

• Cell Theory Concepts:

  1. All living things are composed of cells.

  2. The cell is the basic unit of structure and function in living organisms.

  3. All cells arise from pre-existing cells.

  4. Cells carry genetic information passed to offspring.

• The study of cells is called: Cytology

• Main parts of the cell:

  • Plasma membrane

  • Cytoplasm

  • Nucleus

Plasma Membrane Structure and Function

The plasma membrane is a selectively permeable barrier that surrounds the cell, controlling the movement of substances in and out.

• Functions of the plasma membrane:

  1. Physical isolation

  2. Regulation of exchange with the environment

  3. Sensitivity to the environment

  4. Structural support

• Selective permeability: The plasma membrane allows certain molecules to pass while restricting others, based on size, charge, and solubility.

Membrane Transport Mechanisms

Cells use various mechanisms to transport substances across the plasma membrane, including passive and active processes.

• Passive transport: Movement of substances without energy input (e.g., diffusion, osmosis).

• Active transport: Movement of substances against a concentration gradient, requiring energy (ATP).

• Diffusion: The movement of molecules from an area of higher concentration to lower concentration.

• Osmosis: The diffusion of water across a selectively permeable membrane.

• Simple diffusion vs. osmosis:

  • Both are passive processes.

  • Simple diffusion involves solutes; osmosis involves water.

• Carrier-mediated transport: Transport of substances via membrane proteins; includes facilitated diffusion and active transport.

• Types of carrier-mediated transport:

  1. Facilitated diffusion (passive)

  2. Active transport (requires ATP)

Effects of Solutions on Cells

Cells respond differently to various external solutions based on their tonicity.

Solution Type	Effect on Red Blood Cell
Isotonic	No net movement of water; cell remains normal
Hypotonic	Water enters cell; cell swells and may burst (lysis)
Hypertonic	Water leaves cell; cell shrinks (crenation)

Bulk Transport Processes

Cells use bulk transport to move large particles or volumes across the membrane.

• Endocytosis: Process of taking substances into the cell by engulfing them in a vesicle.

• Exocytosis: Process of expelling substances from the cell by merging vesicles with the plasma membrane.

Cytoplasm and Organelles

The cytoplasm is the material within the cell, excluding the nucleus, and contains various organelles with specialized functions.

• Cytoplasm vs. Cytosol: Cytoplasm includes cytosol (fluid) and organelles; cytosol is the liquid portion.

• Functions of organelles:

  • Nucleus: Stores genetic material (DNA); controls cell activities.

  • Mitochondria: Produces ATP via cellular respiration.

  • Endoplasmic reticulum (ER): Synthesizes proteins (rough ER) and lipids (smooth ER).

  • Golgi apparatus: Modifies, sorts, and packages proteins and lipids.

  • Lysosome: Digests cellular waste and foreign material.

  • Peroxisome: Breaks down fatty acids and detoxifies harmful substances.

  • Microvilli: Increases surface area for absorption.

  • Cilia: Moves substances across cell surface.

  • Flagella: Enables cell movement (e.g., sperm cells).

Genetic Material and Protein Synthesis

DNA and genes are essential for storing and transmitting genetic information and directing protein synthesis.

• DNA: Deoxyribonucleic acid; contains genetic instructions for development and function.

• Gene: Segment of DNA that codes for a specific protein.

• Active transport pump: The sodium-potassium pump ($Na^+/K^+$ pump) maintains ion gradients across the plasma membrane by moving $3 Na^+$ out and $2 K^+$ in per ATP molecule.

Chapter 3: Cell Division and Genetics

Cell Cycle and Mitosis

The cell cycle describes the sequence of events in cell growth and division, including interphase and mitosis.

• Interphase: Period of cell growth and DNA replication; includes G1, S, and G2 phases.

• Mitosis: Division of the nucleus resulting in two identical daughter cells.

• Stages of mitosis:

  1. Prophase: Chromosomes condense, spindle fibers form.

  2. Metaphase: Chromosomes align at the cell equator.

  3. Anaphase: Sister chromatids separate to opposite poles.

  4. Telophase: Nuclear membranes reform, chromosomes decondense.

• Spindle fibers: Essential for chromosome separation; failure leads to abnormal cell division.

Cellular Abnormalities and Cancer

Mutations in cell cycle control can lead to uncontrolled cell division and cancer.

• Metastasis: Spread of cancer cells from the original site to other parts of the body.

• Cellular differentiation: Process by which cells become specialized in structure and function.

• Malignant cells: Cells that divide uncontrollably and can invade other tissues.

Key Equations and Concepts

• Diffusion rate equation: $J = -D \frac{dC}{dx}$ Where $J$ is the flux, $D$ is the diffusion coefficient, and $\frac{dC}{dx}$ is the concentration gradient.

• Sodium-potassium pump equation: $3 Na^+_{out} + 2 K^+_{in} + ATP \rightarrow 3 Na^+_{out} + 2 K^+_{in} + ADP + P_i$

Example: In a hypotonic solution, a red blood cell will swell due to water influx and may burst. In a hypertonic solution, it will shrink as water leaves the cell.

Additional info: Some definitions and explanations have been expanded for clarity and completeness.