2.4 C ELL M EMBRANE

P RE -T EST : L ABEL AS MANY PARTS AS YOU CAN OF THE BELOW DIAGRAM

S TRUCTURE OF M EMBRANES – Draw and label a diagram to show the structure of membranes

L ETS DRAW ONE TOGETHER !

A PROPER D IAGRAM

F UNCTIONS OF A PLASMA MEMBRANE 1. Hold the cell together 2. Control what goes in and out through diffusion, osmosis and active transport 3. Protect the cell 4. Allow the cell to recognize and be recognized (cell signaling and immunity) 5. Bind to other cells and molecules 6. A site for biochemical reactions (enzymes)

T HE PHOSPHOLIPID BILAYER What is it? Naturally form a liposome when placed in an aqueous solution Liposomes are formed Because it is the most “energy favorable” position. Phosphate fat 2 layers Hydrophillic (water loving) Hydrophobic (water fearing) Outside layer - ? Inside layer - ?

B UBBLES ! Using the materials provided, use bubbles to model the following tasks: Observe the fluid lateral movement of the membrane Make an opening in a flat membrane without breaking the membrane Make model prokaryotes (bubbles) and eukaryotes (bubble within bubble) Demonstrate membrane fusion by joining two bubbles Demonstrate selective permeability by passing materials through the membrane without breaking it.

F LUID M OSAIC M ODEL Fluid – constantly moving Mosaic – many pieces put together Model – representation of the real thing Reminds us that the membrane is fluid and flexible, while still being made of many parts. Corn Starch Lateral Movement

S ELECTIVE P ERMEABILITY Controlled entry/exit of materials The concept of “like-dissolves-like” holds here as well. How did we see this in the bubble lab? The size and the charge of a molecule will determine its ability to move through the membrane. Polar heads of the molecule – attracted to other polar molecules Non-polar tails – will repel any charged molecule, therefore preventing passage of ions through the membrane

T YPES OF T RANSPORT Some molecules pass through easily, and can therefore be moved through diffusion Other molecules need a channel and utilize facilitated diffusion Other small molecules need energy (ATP) to move them through, and those are transported through by active transport Large molecules use their own membranes, and are moved past the cell membrane by endo/exocytosis

S OLUTIONS A solution is a mixture of solutes dissolved in a solvent A concentration is all about the amount of solute dissolved in the solution

B ROWNIAN M OTION Brownian motion is the random movement of particles through a solution (liquid or gas). This grumpy guy also discovered and named the nucleus as we see it in eukaryotic cells. Pretty amazing! His original experiment involved pollen particles in water as the model particles.

D IFFUSION Diffusion involves the passive movement of molecules from regions of high concentration to low concentration How would the salt molecules move in this scenario? Passive = no energy Net = overall movement Concentration gradient = the difference between concentration of two different compartments in a system High to low = down the concentration gradient Diffusion only occurs if a membrane is permeable to the substance

D IFFERENCE IN THE RATE OF DIFFUSION Based on this diagram, which scenario would you see a higher rate of diffusion?

D IFFERENCE IN THE RATE OF DIFFUSION Based on this diagram, which scenario would you see a higher rate of diffusion? A higher concentration gradient leads to an increased rate of diffusion as molecules have more energy and move more quickly

O THER F ACTORS THAT AFFECT THE RATE OF DIFFUSION Surface Area It is for this reason that cells can get only so big! We see adaptations in biology to increase surface area in all parts of the body Length of the diffusion path Villi in the intestineAlveoli in Lungs

P ASSIVE T RANSPORT Passive transport is made up of simple diffusion and facilitated diffusion This is due to a net movement of particles from one side of the membrane to the other (Brownian movement) that goes down the concentration gradient Simple Diffusion Occurs when a molecule’s properties allow it to cross the membrane Facilitated Diffusion Occurs if molecules cannot cross easily, but the cell still needs them often (i.e. polar molecules) The rate is affected by: Concentration gradient SA:Volume Ratio Length of diffusion Pathway Channel proteins are integral proteins that allow molecules through the membrane

F ACILITATED D IFFUSION IS THE MOVEMENT OF PARTICLES DOWN THE CONCENTRATION GRADIENT MOVING THROUGH CHANNEL PROTEINS ( TYPE OF INTEGRAL PROTEINS ) Requires a selectively permeable membrane – what types of molecules would require this type of transport? Depends on the properties of the molecule Each channel protein is specific to the molecule it allows through Again – we are moving down the concentration gradient, so this is a type of passive transport

F ACILITATED D IFFUSION IS THE MOVEMENT OF PARTICLES DOWN THE CONCENTRATION GRADIENT MOVING THROUGH CHANNEL PROTEINS ( TYPE OF INTEGRAL PROTEINS ) E XAMPLES Aquaporins – example of facilitated diffusion Voltage-gated ion channels

O SMOSIS – T HE OTHER PASSIVE TRANSPORT Osmosis is the passive net movement of water molecules from regions of low solute concentration to high solute concentration, through a selectively permeable membrane This is often due to the fact that a membrane is impermeable to the solute This is a passive process And we are still moving down the concentration gradient Low Water High Water High solute Low Solute

O SMOSIS IS THE PASSIVE NET MOVEMENT OF WATER MOLECULES FROM REGIONS OF LOW SOLUTE CONCENTRATION TO HIGH SOLUTE CONCENTRATION, THROUGH A SELECTIVELY PERMEABLE MEMBRANE

O SMOSIS IN ACTION

C OMPARING D IFFUSION AND O SMOSIS Osmosisvs. Diffusion SimilarBoth are PassiveBoth move down the concentration gradient DifferentDiffusion is of solutes Membrane not needed Osmosis only works with water Partially-permeable membrane essential

A CTIVE T RANSPORT – U SES ENERGY, IN THE FORM OF ATP, TO MOVE MOLECULES AGAINST THE CONCENTRATION GRADIENT. Molecules cannot pass through the membrane Active transport is the key in homeostasis in organisms, such as in the resetting of nerves after impulses have passed through

A CTIVE T RANSPORT

V ESICLE T RANSPORT Vesicles transport macromolecules (those that are too large for diffusion or protein channels) and newly formed molecules such as proteins Vesicles are formed from the phospholipid bilayer of the organelle, and serve to protect it as it moves through the cytoplasm budding fusing

V ESICLE F USING Step 1 - Two vesicles come close together to begin to interact.

Given that the membranes are made of like materials, they can begin to fuse together The phospholipids from one membrane meld with the other membrane, and so an intermediate membrane is formed for a brief moment V ESICLE F USING

The two vesicles fuse together further, and the intermediate membrane gets wider.

V ESICLE F USING Finally the membranes are fully fused. This allows contents from both to be integrated into each other. In the case of intracellular vesicle transport, this would be the fusing of the vesicle with another organelle For extracellular transport, this would be the fusing of a vesicle with the cell membrane

H OW VESICLES FUSE Step 1 Step 2 Step 3 Step 4 NOTICE! There is never a broken section of the bilayer throughout this whole process.

V ESICLE T RANSPORT IN ACTION Vesicle transport is the mechanism of all inter-neuron communication It is also important in the releasing of hormones in to the blood stream

A PPLICATIONS OF P HOSPHOLIPIDS IN MEDICINE Pharmacists are constantly using liposomes to transport drugs around the body and deliver them to cells. The $$ question to be able to answer: How do you deliver it to the right cells? Tons of potential cancer treatments b/c of the “slack” structure of cancer cell colonies.