03 PT 1

Studying Cells

• Cytology – The study of the structure and function of cells.

• Light Microscopy (LM) – Uses visible light to magnify cell structures. Can observe live or stained cells but has limited resolution.

• Electron Microscopy (EM) – Uses electron beams for high-resolution imaging of cells.

• Scanning Electron Microscopy (SEM) – Provides a 3D view of the cell’s surface.

• Transmission Electron Microscopy (TEM) – Provides detailed images of internal cell structures.

Cell Theory

• Basic Concepts of Cell Theory:

• All living things are made of cells.

• Cells are the basic units of life.

• All cells arise from pre-existing cells.

• Cells are the fundamental units of homeostasis.

Overview of Cell Anatomy

• Extracellular Fluid (Interstitial Fluid) – Fluid surrounding cells that provides nutrients and removes waste.

• Cell Membrane (Plasma Membrane) – A lipid bilayer that separates the cell from the external environment.

• Cytoplasm – The fluid inside the cell that contains cytosol and organelles.

• Cytosol – The intracellular fluid containing ions, proteins, and dissolved nutrients.

• Organelles – Specialized structures within the cytoplasm that perform specific functions.

The Cell Membrane

• Functions of the Plasma Membrane:

• Physical Isolation – Separates the cell from the external environment.

• Regulation of Exchange – Controls what enters and exits the cell.

• Sensitivity – Responds to environmental changes.

• Structural Support – Provides shape and strength.

• Membrane Structure:

• Phospholipid Bilayer – Two layers of phospholipids with hydrophilic heads and hydrophobic tails.

• Membrane Proteins:

• Receptors – Detect signals from the environment.

• Channels – Allow specific molecules to pass through.

• Carriers – Transport substances across the membrane.

• Enzymes – Catalyze reactions on the membrane.

• Anchors – Attach the membrane to the cytoskeleton.

• Identifiers – Help the immune system recognize self vs. foreign cells.

Membrane Transport

• Selective Permeability – The ability of the membrane to control which substances enter or exit the cell.

• Factors Affecting Permeability:

• Molecular Size – Smaller molecules pass through more easily.

• Electrical Charge – Charged molecules may require transport proteins.

• Molecular Shape – Only molecules of the correct shape fit through transport proteins.

• Lipid Solubility – Lipid-soluble molecules pass more easily.

• Types of Membrane Transport:

• Passive Transport (no ATP required):

• Diffusion – Movement of molecules from high to low concentration.

• Osmosis – Movement of water across a membrane to balance solute concentrations.

• Filtration – Movement due to hydrostatic pressure (e.g., in kidneys).

• Carrier-Mediated Transport:

• Facilitated Diffusion – Transport proteins help molecules move down a concentration gradient.

• Active Transport – Moves molecules against a concentration gradient using ATP (e.g., Sodium-Potassium Pump).

• Vesicular Transport:

• Endocytosis – Bringing substances into the cell.

• Receptor-Mediated Endocytosis – Specific molecules bind to receptors before being engulfed.

• Pinocytosis – “Cell drinking”; ingestion of fluids.

• Phagocytosis – “Cell eating”; engulfing large particles.

• Exocytosis – Expelling materials from the cell.

• Osmotic Effects on Cells:

• Isotonic Solution – No net movement of water; cell remains stable.

• Hypertonic Solution – Water moves out of the cell, causing it to shrink (crenation).

• Hypotonic Solution – Water moves into the cell, causing it to swell and possibly burst (lysis).