Lecture Notes: Chapter 3 - Cell Structure and Function

Overview

• Importance of Cells: Understanding cell structure and function is crucial to understanding how organs and organ systems function.
• Key Focus: Cell membrane structure, organelles, and their functions.

Cell Membrane

• Definition: A cell membrane is a coating that surrounds the cell, made up primarily of phospholipids, cholesterol, and proteins.
• Basic Components:
  • Phospholipids: Form a bilayer with hydrophilic heads and hydrophobic tails.
  • Cholesterol: Provides structure and support.
  • Proteins: Various types including transmembrane proteins, glycoproteins, and lipid-anchored proteins.
• Functions:
  • Acts as a semi-permeable barrier.
  • Regulates movement of substances due to concentration and electrical gradients.
  • Facilitates communication between cells via signaling molecules and protein interactions.
• Structural Complexity: Contains glycoproteins, glycolipids, and cytoskeletal elements for stability and function.

Fluid Environment

• Intracellular Fluid (ICF): Fluid inside cells.
• Extracellular Fluid (ECF): Fluid outside cells, including interstitial fluid and plasma in the blood.

Organelles

• Nucleus:

  • Contains DNA organized into chromatin or chromosomes.
  • Surrounded by a nuclear envelope with pores for material passage.
  • Nucleolus: Site of RNA synthesis.

• Mitochondria:

  • Site of ATP production, “powerhouse” of the cell.
  • Contains its own DNA (maternal origin).

• Endoplasmic Reticulum (ER):

  • Rough ER: Has ribosomes; synthesizes and modifies proteins.
  • Smooth ER: No ribosomes; synthesizes lipids and steroids.

• Golgi Apparatus:

  • Modifies, packages, and secretes proteins.

• Lysosomes & Peroxisomes:

  • Digestive organelles for waste processing and cellular detoxification.

Cellular Components

• Cytoskeleton:

  • Provides structural support made up of microtubules, microfilaments, and intermediate filaments.
  • Involved in cell shape, movement, and division.

• Ribosomes:

  • Sites of protein synthesis.

• Microvilli, Cilia, and Flagella:

  • Microvilli: Increase surface area for absorption, do not move.
  • Cilia: Move fluid over cell surfaces.
  • Flagella: Propel sperm cells.

Cell Junctions

• Types of Junctions:
  • Gap Junctions: Allow communication between cells; important in cardiac cells.
  • Tight Junctions: Prevent passage of substances between cells (intestinal lining).
  • Anchoring Junctions: Provide mechanical support and stability to tissues.

Cellular Processes

• Secretion:

  • Exocrine glands secrete substances via ducts (e.g., sweat, mucus).
  • Endocrine glands secrete hormones directly into the bloodstream.

• Cell Death (Apoptosis):

  • Programmed cell death to remove old, damaged cells without harming surrounding cells.
  • Necrosis: Uncontrolled cell death, releases harmful substances.

• Cell Replacement:

  • Stem Cells: Can divide and replace cells under certain conditions.
  • Research on stem cells focuses on their potential to replace damaged tissues.