Moving materials in and out of the cell. Cell Transport Moving materials in and out of the cell.

Cell Membrane “Fluid Mosaic Model” (fluid with a mosaic of proteins) Phospholipid Bilayer- phosphate head, lipid tail Amphipathic – a molecule that’s hydrophobic and hydrophilic.

Selective Permeability Semi-permeable – allows only some materials through** Small nonpolar molecules, such as hydrocarbons, can dissolve in the lipid bilayer Large Polar molecules, such as sugars, do not cross the membrane easily

Freeze Fracture Freeze-fracture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer

Maintaining Fluidity The phospholipids constantly trade places from side to side. Every once in a while they will trade with a phospholip from the other layer. High temperatures cause more movement, lower temperatures cause less.

Observing Phospholipid Movement When placed together, the phopholipids of a mouse and human cell ended up mixed due to all the movement.

Cholesterol Cholesterol – a steroid hormone found in membranes to help maintain fluidity. It restricts excessive movement at high temps. It prevents sticking together at low temps.

Membrane Proteins Integral Proteins – go through the whole membrane Peripheral Proteins – sit on the outside of the membrane (inside of the cell).

Protein Roles Cell membrane proteins do six main things 1. Transport materials in and out, 2. Act as Enzymes, 3. Pass signals.

Protein Roles 4. Identify other cells, 5. connect to other cells, 6. attach the cytoskeleton to the ECM fibers

Carbohydrate Roles Carbohydrates can bond to the lipids (glycolipids) or more often proteins (glycoproteins) in the membrane to aid in cell recognition, by protruding from the membrane.

Passive Transport Passive Transport- requires no energy

Diffusion Simple Diffusion- molecules move from an area of higher concentration to lower concentration (down their concentration gradient) occurs until equilibrium is reached (molecules are evenly spread out) Ex. cologne

Diffusion across a membrane

Osmosis Osmosis- diffusion of water molecules thru a selectively permeable membrane (high to low water concentration) the force exerted by osmosis is called osmotic pressure

Osmosis continued

Cell in Solution Hypertonic solution – more dissolved material in solution than in the cell (water flows out of the cell) ** hypertonic

Cell in Solution Hypotonic solution -more dissolved material in the cell than in the solution, causing (water flows into the cell) (increases osmotic pressure, cells may burst). hypotonic

Isotonic Isotonic- same amount of dissolved material in the solution and cell. (equilibrium is reached) Isotonic

Osmoregulation (control of water balance) Why don’t cells burst? cells in organisms don’t usually come into contact with pure water plant cells have cell walls that keep the cell from expanding some cells use pumps

Facilitated Diffusion Facilitated diffusion - diffusion with the assistance of integral transport proteins. (Still Passive transport)

Channel Proteins Channel Proteins – allow certain materials to flow in and out (down their concentration gradient.) Aquaporin – channel protein that only lets water in. Ion Channels – also called gated channels, open and close in response to a chemical or electrical stimulus

Carrier Proteins Carrier Proteins – change shape to escort certain material in and out of the cell. (down their concentration gradients.)

Active Transport Active transport - requires energy Proteins act as pumps to move material from low to high concentration. (often called electrogenic pumps) Ex. Proton Pumps (Hydrogen Pumps)

Pumps continued Sodium-Potassium pump – pumps sodium out and potassium in. (low to high concentration)

Electrochemical Gradient Pumps create a build up of ions on either side of the membrane, which creates an electric charge. The charge causes an electrochemical gradient, which moves the ions across the membrane like an electric current to do work. (ex. Nerve signals)

Cotransport Cotransport – electrochemical gradient used to move other molecules across the membrane

Moving large objects Endocytosis – a vesicle formed to take materials into the cell** Exocytosis – a vesicle putting materials out of the cell

3 Types of Endocytosis 1. Phagocytosis – engulfing solid particles 2. Pinocytosis – engulfing liquid substances (extracellular fluid)

3 Types of Endocytosis Receptor mediated endocytosis – particles called ligands bind to receptors, which signals the engulfing of the particles.

You should now be able to: Define the following terms: amphipathic molecules, aquaporins, diffusion Explain how membrane fluidity is influenced by temperature and membrane composition Distinguish between the following pairs or sets of terms: peripheral and integral membrane proteins; channel and carrier proteins; osmosis, facilitated diffusion, and active transport; hypertonic, hypotonic, and isotonic solutions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Explain how transport proteins facilitate diffusion Explain how an electrogenic pump creates voltage across a membrane, and name two electrogenic pumps Explain how large molecules are transported across a cell membrane Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings