2.4 CELL MEMBRANE
Jan 04, 2016
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.