The Cell Membrane: Phospholipid Bilayer

Learning Objectives What is diffusion What are the unique features for the cell membrane (be able to draw it too) Why must a cell membrane also have proteins What different Roles do membrane proteins serve

Simple Diffusion pg185 Movement of substances from regions of higher concentration to regions of lower concentration Diffusion of water across a membrane is called OSMOSIS Can also apply to oxygen, CO2 and lipid-soluble substances

The Cell Membrane: Phospholipid Bilayer Pg 182 The Cell Membrane: Phospholipid Bilayer

Phospholipids – Makes up the cell membrane This O–Atom has a negative charge This N–Atom has a positive charge

Phospholipids- makes up the cell membrane This N–Atom has a positive charge This O–Atom has a negative charge Phospholipids- makes up the cell membrane

Hydrophilic vs. Hydrophobic Hydrophilic = Water loving Hydrophobic = Water fearing

Phospholipids and water Remember: water has POLAR covalent bonds

Charges on the Phosphate & Nitrogen makes the head region hydrophilic (likes water) The Tails have no charge, they are just long carbohydrate chains (like other lipids) that are non-polar so they are hydrophobic (hates water) and so they will only interact with other non-polar molecules like other lipids (cholesterol) and each other (tails always face each other) The Phospholipid Bilayer is a key part of the Fluid Mosaic Model that makes up the outer most layer of cells.

The Phospholipid Bilayer is a key part of the Fluid Mosaic Model that makes up the outer most layer of cells. Helps controls what moves in and out of cell (food, wastes, viruses) Cholesterol (lipid) stabilizes the membrane

This Selective Permeability of the membrane means that: 1 This Selective Permeability of the membrane means that: 1. Some things can cross freely (in or out) 2. Some things are never allowed to cross at all 3. And some things need assistance to cross the membrane…

….certain proteins “sit” in the bilayer and help with interaction between the outside environment and the internal areas of the cell. These are called Transport Proteins

Transport Proteins Transport proteins can act like: Channels (no energy needed)  FACILITATED DIFFUSION Carriers (no energy needed)  like water wheels: not in picture Pumps (needs energy)  going against the flow called: ACTIVE TRANSPORT Transport Proteins

(energy) (Channel protein) Transport Proteins

Other Membrane proteins Channels, carriers, pumps Receptors (muscle, nerve cells) Enzymes (start or stop enzyme from working) Self-markers (identifies the cell to other cells) “Anchors” to other cells

Look under “Lipids” &“Membrane Transport” NA – K+ Pump protein http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter6/animations.html# Look under “Lipids” &“Membrane Transport” http://www.stolaf.edu/people/giannini/biological%20anamations.html http://www.stolaf.edu/people/giannini/flashanimat/metabolism/2nd%20messenger.swf

Intercellular Junctions Tight junctions close space between cells located among cells that form linings Intercellular Junctions Desmosomes form “spot welds” between cells located among outer skin cells Gap junctions tubular channels between cells located in cardiac muscle cells End

Crossing…………………………….…Over