2.4 C ELL M EMBRANE. P RE -T EST : L ABEL AS MANY PARTS AS YOU CAN OF THE BELOW DIAGRAM.

2.4 CELL MEMBRANE

PRE-TEST: LABEL AS MANY PARTS AS YOU CAN OF THE BELOW DIAGRAM

STRUCTURE OF MEMBRANES

2.4.1 – Draw and label a diagram to show the structure of membranes

LETS DRAW ONE TOGETHER!

A PROPER DIAGRAM

FUNCTIONS 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)

THE PHOSPHOLIPID BILAYER

What is it? Naturally form a liposome when placedin an aqueous solution

Liposomes are formedBecause it is the most “energy favorable” position.

Phosphate fat 2 layers

Hydrophillic (water loving)

Hydrophobic (water fearing)

Outside layer - ?Inside layer - ?

BUBBLES!

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.

FLUID MOSAIC MODEL

Fluid – constantly moving Mosaic – many pieces put together Model – representation of the real thing

http://www.bio.davidson.edu/people/macampbell/111/memb-swf/membranes.swf

• Reminds us that the membrane is fluid and flexible, while still being made of many parts.

• Corn Starch • Lateral Movement

SELECTIVE PERMEABILITY 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

TYPES OF TRANSPORT

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

SOLUTIONS

A solution is a mixture of solutes dissolved in a solvent

A concentration is all about the amount of solute dissolved in the solution

BROWNIAN MOTION

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 modelparticles.

DIFFUSION

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 movementConcentration gradient = the difference between concentration of two different compartments in a systemHigh to low = down the concentration gradient

Diffusion only occurs if a membrane is permeable to the substance

DIFFERENCE IN THE RATE OF DIFFUSION

Based on this diagram, which scenario would you see a higher rate of diffusion?

DIFFERENCE 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

OTHER FACTORS 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 intestine Alveoli in Lungs

PASSIVE TRANSPORT

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 DiffusionOccurs when a molecule’s properties allow it to cross the membrane

Facilitated DiffusionOccurs 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

FACILITATED DIFFUSION 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

FACILITATED DIFFUSION IS THE MOVEMENT OF PARTICLES DOWN THE CONCENTRATION GRADIENT MOVING THROUGH CHANNEL PROTEINS (TYPE OF INTEGRAL PROTEINS) EXAMPLES

Aquaporins – example of facilitated diffusion

Voltage-gated ion channels

OSMOSIS – THE 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 downthe concentration gradient

Low Water High Water

High solute Low Solute

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

OSMOSIS IN ACTION

COMPARING DIFFUSION AND OSMOSIS

Osmosis vs. Diffusion

Similar Both are Passive Both move down the concentration gradient

Different Diffusion is of solutesMembrane not needed

Osmosis only works with waterPartially-permeable membrane essential

ACTIVE TRANSPORT – USES 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

ACTIVE TRANSPORT

VESICLE TRANSPORT• 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

VESICLE FUSING

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

VESICLE FUSING

VESICLE FUSING

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

VESICLE FUSING

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

HOW VESICLES FUSE

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

VESICLE TRANSPORT 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

http://www.sumanasinc.com/webcontent/animations/content/vesiclebudding.html

APPLICATIONS OF PHOSPHOLIPIDS 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.