The Plasma Membrane Chapter 5 (pgs )

Plasma Membrane

Plasma membrane is a loose, lipid structure Fluid-mosaic model

Functions of the Plasma Membrane Isolates the outside of the cell from the environment Controls what enters and leaves the cell therefore, it’s a semi-permeable membrane Selective as to what enters the cell and the direction molecules travel

Plasma Membrane is made up of: Phospholipid bilayer two-layers of phospholipids fluid in nature hydrophobic and other small molecules can pass through Contains proteins structural support, signaling or communication, recognition, passage or transport 2 types: Integral = span the membrane Peripheral = on surface

Plasma Membrane is made up of: Contains cholesterol between phospholipid molecules used for “patching” so small molecules can’t get through helps keep optimum fliudity Glycocalyx short branched carbohydrate extensions coming off of proteins used as binding sites for signaling molecules

General Movement of Molecules 1.Diffusion: movement from high concentration to lower concentration Ex. Glass of water and you add red dye Occurs with odors; occurs in plants

Movement of Molecules 1.Diffusion: movement from high concentration to lower concentration Ex. Glass of water and you add red dye Occurs with odors; occurs in plants 2. Osmosis: movement of water across a semi- permeable membrane from low concentration to high concentration Yes, it is going against gravity! Ex. When a plant wilts; why preservatives are put into food products; how the fluid part of blood is put back into your blood vessels

Osmosis 1.Hypertonic solution: greater concentration of solutes (ex. salts) outside the cell than inside the cell So water moves out of the cell and the cell shrinks Ex. Egg in syrup 2. Isotonic solution: solute concentration inside and outside the cell are equal Ex. Egg 3. Hypotonic solution: greater concentration of solutes inside the cell than outside the cell So water moves into the cell and the cell expands Ex. Egg in vinegar

Movement of Small Molecules in Cells 1.Passive transport A. Simple diffusion: diffuses through a membrane from high concentration to low concentration; no energy required Ex. How oxygen and carbon dioxide get into and out of our cells “Smelly balloons” demo!

Movement of Small Molecules in Cells 1.Passive transport A. Simple diffusion: diffuses through a membrane from high concentration to low concentration Ex. How oxygen and carbon dioxide get into and out of our cells B. Facilitated diffusion: movement from high concentration to low concentration through a membrane with the help of a protein; no energy required

Example of facilitated diffusion Molecules randomly move through the integral protein Molecules move from an area of high concentration to an area of low concentration High Concentration Low Concentration

Example of facilitated diffusion (Animation by Jim Sullivan) Molecules randomly move through an integral protein Molecules move from an area of high concentration to an area of low concentration

Example of facilitated diffusion Peripheral proteins don’t extend through the membrane Proteins bind and drag the molecules through the lipid bilayer and releases the molecules on the opposite side High Concentration Low Concentration

Example of facilitated diffusion (Animation by Jim Sullivan) Peripheral proteins don’t extend through the membrane Proteins bind and drag the molecules through the lipid bilayer and releases the molecules on the opposite side

Movement of Small Molecules in Cells 1.Passive transport A. Simple diffusion B. Facilitated diffusion 2. Active transport: movement through a transport protein movement against a concentration gradient requires energy = ATP Ex. Storage of glucose in the liver Ex. Sodium-potassium pump Low Conc. High Conc.

Movement of Large Molecules in Cells 1.Exocytosis: movement out of a cell through the formation of a vesicle Ex. proteins; the release of digestive enzymes; mucus

Movement of Large Molecules in Cells 1.Exocytosis: movement out of a cell through the formation of a vesicle Ex. Proteins; digestive enzymes; mucus 2. Endocytosis: movement into a cell

Types of Endocytosis 1. Pinocytosis: “cell-drinking” because its bringing into the cell fluids with materials suspended in it Ex. Movement of blood

Types of Endocytosis 3. Phagocytosis: “cell-eating” because it brings into the cell large materials Ex. Bacteria; cell debris

Types of Endocytosis 2. Receptor-mediated endocytosis: specialized cell surface receptors bind to molecules and pulls it into the cell Ex. Transport of iron

Plant cells: Cell wall: maintains structure; protection from environment; limits water absorption Central vacuole: storage of nutrients; gets rid of waste products; maintains pH; enzymes for digestion; contains pigments Plastids: storages nutrients; contains pigments; needed for photosynthesis (chloroplast) Amyloplast: makes starch Do not contain lysosomes…in animals only!!!