Cell Transport and Membrane Structure

Cell Membrane Basics

• Selectively Permeable: The cell membrane has the ability to choose which substances can enter and leave the cell.

• Composition:

  • Lipid Bilayer: Composed of two layers of phospholipids.

  • Proteins: These include channel proteins and pumps that facilitate transport across the membrane.

• Function: The primary function of the cell membrane is to maintain a balanced internal environment while allowing necessary materials to flow in and out of the cell.

Types of Cellular Transport

• Two main categories of cellular transport:

  1. Passive Transport:

  • No energy (ATP) required.

  • Molecules move from an area of high concentration to an area of low concentration.

  1. Active Transport:

  • Requires energy (ATP).

  • Molecules move from an area of low concentration to high concentration (against the concentration gradient).

Passive Transport

• Characteristics: No energy is required; movement occurs along the concentration gradient.

  • Types of Passive Transport:

  1. Diffusion:

     • Involves the movement of small molecules (e.g., $O2$, $CO2$).

     • Molecules naturally move from high to low concentration.

  2. Facilitated Diffusion:

     • Similar high to low movement, but involves protein channels for moving larger molecules (e.g., glucose).

  3. Osmosis:

     • The specific type of diffusion concerning water.

     • Water molecules move toward the area of higher solute concentration.

Osmosis: Tonicity

• How solutions affect a cell:

  1. Hypertonic:

  • Defined as having more solute outside the cell.

  • Causes water to move out of the cell, resulting in cell shrinkage (plasmolysis).

  1. Hypotonic:

  • Defined as having less solute outside the cell.

  • Causes water to move into the cell, leading to swelling and possibly bursting (lysis).

  1. Isotonic:

  • Equal solute concentration on both sides of the membrane.

  • Water moves equally in both directions; cell maintains its normal state.

Active Transport

Characteristics

• Requires energy (ATP) to move molecules against their concentration gradient (from low to high).

Types of Active Transport

• Types:

  1. Protein Pumps:

  • Membrane proteins utilize ATP to pump molecules against the concentration gradient.

  • Example: Sodium-Potassium Pump.

  1. Endocytosis:

  • Process where the cell engulfs large materials by folding its membrane inward.

    • Phagocytosis: Cell 'eats' solid particles.

    • Pinocytosis: Cell 'drinks' liquids.

  1. Exocytosis:

  • The process of releasing materials out of the cell using vesicles.

Comparing Passive vs Active Transport

• Passive Transport:

  • Characteristics:

  • Movement: High → Low concentration.

  • No ATP required.

  • Includes processes: diffusion, osmosis, facilitated diffusion.

  • May involve protein channels.

  • Small or nonpolar molecules easily traverse.

  • Active Transport:

  • Characteristics:

    • Movement: Low → High concentration.

    • Requires ATP.

    • Includes mechanisms such as pumps, endocytosis, and exocytosis.

    • Typically involves movement of large molecules or ions.

  • Works against the concentration gradient.

• Commonalities:

  • Both transport types move materials across the cell membrane.

  • Utilize membrane proteins.

  • Essential for maintaining homeostasis.

Special Notes from Worksheets

• Diffusion Facts:

  • Molecules naturally spread out to balance concentrations.

  • Rate of diffusion depends on factors such as temperature and concentration gradients.

• Cell Membrane Structure Notes:

  • Phospholipid Heads: Hydrophilic (water-loving).

  • Tails: Hydrophobic (water-fearing).

  • Proteins function as pathways or 'doors' for substances.

• Cell Reactions in Solutions:

  • Hypertonic: Cells shrink.

  • Hypotonic: Cells expand.

  • Isotonic: Cells remain unchanged.

• Transport Diagram Notes:

  • Facilitated diffusion uses protein assistance without energy.

  • Active transport is energy-dependent, utilizing ATP and proteins.

  • Endocytosis and exocytosis involve vesicles.

Quick Vocabulary

• Word Meanings:

  • Solute: Substance that is dissolved (e.g., salt, sugar).

  • Solvent: Substance doing the dissolving (e.g., water).

  • Gradient: The difference in concentration between two areas.

  • Homeostasis: The maintenance of stable internal conditions within a cell.

  • Vesicle: A membrane-bound 'bubble' used in transport.

Practice Questions

1. Water moves from a ___ solute concentration to a ___ solute concentration. → Low → High.

2. Which type of transport uses energy? → Active Transport.

3. What type of solution makes a cell shrink? → Hypertonic.

4. What process does a cell use to take in large particles? → Endocytosis.

5. What process moves molecules from high to low through proteins? → Facilitated Diffusion.

Mnemonic to Remember Tonicity

• Hyper: The water hyper runs OUT.

• Hypo: Hippo → cell gets big.

• Iso: "I so feel normal."

Organelles and Their Functions

1. Cell Membrane: Regulates what enters and leaves the cell.

2. Cytoplasm: Holds and supports the cellular components and facilitates movement within the cell.

3. Ribosome: The site of protein synthesis in the cell.

4. Nucleus: Houses the cell's DNA, which contains instructions for building proteins.

5. Endoplasmic Reticulum (ER):

   • Smooth ER: Processes lipids and carbohydrates; does not have ribosomes.

   • Rough ER: Studded with ribosomes; processes proteins for export from the cell.

6. Golgi Apparatus: Packages and distributes proteins and other materials to their designated locations.

7. Mitochondria: Converts chemical energy from food into usable energy compounds for the cell.

8. Cell Wall: Provides structural support and protection for plant cells.

9. Chloroplast: Converts sunlight, carbon dioxide, and water into sugars via photosynthesis.

10. Vacuole: Serves as storage for water, salts, proteins, and carbohydrates.

Plasma Membrane Details

1. The Plasma Membrane:

   • A thin, flexible boundary between the cell and its aqueous environment.

   • Function: Allows nutrients in and waste out; helps maintain homeostasis (internal balance).

2. Function of Plasma Membrane:

   • Selective Permeability (Semi-permeable): Allows certain substances to pass through while preventing others.

3. Structure of the Plasma Membrane:

   • Phospholipid Bilayer:

     • Composed of two layers of phospholipids arranged tail-to-tail.

     • Structure includes a glycerol backbone, two fatty acid chains, and a phosphate group.

     • Hydrophilic Heads: Water-loving and polar.

     • Hydrophobic Tails: Water-fearing and non-polar.

     • Water-soluble substances cannot easily pass due to the presence of the hydrophobic tails.

   • Other Components:

     • Proteins:

     • Transmit signals inside the cell.

     • Serve as support structures.

     • Provide pathways for substances to enter and leave the membrane (transport proteins/protein channels).