Cell Membrane Notes - Unit 3

# Cell Membrane ## Cell Membrane aka: "Gatekeeper" Super Important for: - Homeostasis - Bacteria - Plant Cell - Animal Cell ## I. Structure of Cell Membrane ### Cell Membrane in ALL cells - **Fluid Mosaic Model:** the molecules in the cell membrane are not "fixed", but are free to flow among each...

# Cell Membrane ## Cell Membrane aka: "Gatekeeper" Super Important for: - Homeostasis - Bacteria - Plant Cell - Animal Cell ## I. Structure of Cell Membrane ### Cell Membrane in ALL cells - **Fluid Mosaic Model:** the molecules in the cell membrane are not "fixed", but are free to flow among each other like a fluid - **3 Basic Molecules in Membrane:** 1. Phospholipid 2. Proteins 3. Cholesterol ### Video 1: Fluid Mosaic Model ### Video 2: Structure of the Cell Membrane ### 1. Phospholipid Bilayer: 2 layers of phospholipids. **Diagram of phospholipid bilayer:** - **Hydrophilic (polar) head:** likes water - Outside - **Hydrophobic (non-polar) tails:** hates water - Inside ### 2. Surface Proteins can be used to: 1. **Transport:** (Transport Proteins/Ion Channels) 2. **Bind/Attach:** (Anchor Proteins) 3. **Receive signals:** (Receptor Proteins w/binding pockets for signaling molecule) 4. **Catalyze reactions:** (Enzymes) 5. **Identify/Mark:** (Glycoproteins w/sugar "nametags") *Also glycolipids* - Example: blood type ## Types of Proteins: | Protein Type | Details | |---|---| | Integral Proteins | Permanently stuck in membrane (transmembrane: pass all the way through) | | Peripheral Proteins | Only adhere to one side of the membrane | | Cholesterol | Keeps membrane from becoming too rigid or too fluid - increases both stability and movement | ### "Selectively Permeable" Only specific molecules are able to pass through the cell membrane. **YES:** - Oxygen - Carbon Dioxide - Water* **NO:** - Large molecules - Molecules without a charge **Examples:** - Amino acids (build proteins) - Carbohydrates (glucose) - Ions *Water is small but polar, so diffuses slowly, needs extra help to pass through quickly (aquaporins)* *Cells need these, but can't pass through directly. (semipermeable)* ## II. Movement Across the Cell Membrane Happens by: - Diffusion - Facilitated diffusion - Osmosis (diffusion of water) - Cell transport (energy) ### 1. Diffusion: The movement of molecules from where there are many to where there are fewer. *Down concentration gradient.* - No energy required! - Passive transport ### 2. Osmosis: The diffusion of water across a semi-permeable membrane. ### Food Coloring Diffusing In Water - Measuring water is osmosis - Measures other molecules: diffusion ### Diagram of Osmosis: - **Hypertonic solution:** Solute in solution is greater than in the cell - **Isotonic solution:** Amount of solute in solution is the same as in the cell. - **Hypotonic Solution:** Solute in solution is less than in the cell. **Animal Cell:** | Solution | Animal Cell | |---|---| | Hypertonic | Shriveled | | Isotonic | Normal | | Hypotonic | Lysed | **Plant Cell:** | Solution | Plant Cell | |---|---| | Hypertonic | Plasmolyzed | | Isotonic | Flaccid | | Hypotonic | Turgid (normal) | **Dynamic Equilibrium:** Movement of water continues but net movement is 0. ## Types of Diffusion Through the Plasma Membrane **Facilitated Diffusion:** When molecules use a protein to help them go through the cell membrane. **No Energy!** - Passive transport - Changes shape to only let certain molecules pass through. ## Active Transport - Requires energy - ATP (adenosine triphosphate) - Low Concentration to High Concentration - Uses carrier proteins ## Exocytosis - Releases molecules outside the cell - Merges transport vesicle with plasma membrane ## Endocytosis - Takes in molecules inside the cell - Forms a pouch that pinches off to become a vesicle - **Phagocytosis (eat)** - **Pinocytosis (drink)** ## Additional Videos: - Amoeba Feeds - Cell Transport