Cell Structure, Membrane Transport, and Cell Division: Study Guide 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 functions of cells. It provides the foundation for understanding the structure and function of all 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.

Effects of Concentration Gradients

Concentration gradients drive the movement of substances across membranes.

• Oxygen in the lungs: A decrease in oxygen concentration reduces diffusion into the blood.

Solutions and Cell Response

Cells respond differently to various types of solutions based on their tonicity.

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

Carrier-Mediated Transport

Carrier proteins facilitate the movement of specific molecules across the plasma membrane.

• Types:

  1. Facilitated diffusion (passive)

  2. Active transport (requires ATP)

Vesicular Transport

Large molecules are transported via vesicles in processes called endocytosis and exocytosis.

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

• Exocytosis: The process of expelling substances from the cell via vesicles.

Cytoplasm and Cytosol

The cytoplasm is the material within the cell, excluding the nucleus, and contains the cytosol and organelles.

• Cytosol: The fluid portion of the cytoplasm.

• Difference: Cytoplasm includes cytosol and organelles; cytosol is just the liquid.

Cell Organelles and Their Functions

Organelles are specialized structures within cells that perform distinct functions.

Organelle	Function
Nucleus	Contains genetic material (DNA); controls cell activities
Mitochondria	Produces ATP via cellular respiration
Endoplasmic Reticulum	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
Cilia	Move substances across cell surface
Flagella	Enable cell movement

Genetic Material

DNA and genes are essential for heredity and cellular function.

• DNA: Stores genetic information; directs protein synthesis.

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

Active Transport Pump

The sodium-potassium pump is a key active transport mechanism in human cells.

• Function: Moves sodium ions out and potassium ions into the cell against their concentration gradients.

• Equation: $3\,\text{Na}^+_{\text{out}} + 2\,\text{K}^+_{\text{in}} + \text{ATP} \rightarrow 3\,\text{Na}^+_{\text{out}} + 2\,\text{K}^+_{\text{in}}$

Chapter 3: Cell Division and Genetics

Cell Division Overview

Cell division is the process by which cells reproduce, involving both nuclear and cytoplasmic events.

• Two main types:

  • Mitosis: Produces identical daughter cells

  • Meiosis: Produces gametes with half the chromosome number

Interphase and Its Stages

Interphase is the period of cell growth and DNA replication before division.

• Stages of Interphase:

  1. G1 (Gap 1): Cell growth

  2. S (Synthesis): DNA replication

  3. G2 (Gap 2): Preparation for mitosis

Mitosis and Its Stages

Mitosis is the division of the nucleus resulting in two identical daughter cells.

• Stages of Mitosis:

  1. Prophase: Chromosomes condense, spindle forms

  2. Metaphase: Chromosomes align at the cell equator

  3. Anaphase: Sister chromatids separate

  4. Telophase: Nuclear envelopes reform, chromosomes decondense

• Spindle fibers: Essential for chromosome movement; failure leads to improper cell division.

Cell Cycle Disorders

Mutations in cell cycle control can lead to diseases such as cancer.

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

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

Summary Table: Mitosis Stages

Stage	Main Event
Prophase	Chromosomes condense, spindle forms
Metaphase	Chromosomes align at equator
Anaphase	Sister chromatids separate
Telophase	Nuclear envelope reforms

Example: During mitosis, if spindle fibers fail to form, chromosomes cannot be properly separated, leading to abnormal cell division and potential genetic disorders.

Additional info: Some definitions and explanations have been expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.