What are the main functions of the cell membrane? https://ed.ted.com/lessons/cell-membranes-are-way-more-complicated-than-you-think-nazzy-pakpour THE CELL MEMBRANE What are the main functions of the cell membrane?

FUNCTION of the cell membrane: To regulate what enters and what leaves the cell Provides support and protection for the cell The membrane is semi-permeable. :

A semi-permeable membrane

Structure of the Cell Membrane The cell membrane is made of a double layer of phospholipids with proteins embedded in it. The double layer looks like lollipops. - the heads of the phospholipids are hydrophilic (attracted to water) - the tails of the phospholipids are hydrophobic (fear water)

WHY PHOSPHOLIPID BILAYER? The phospholipid layer maintains the shape and integrity of the cell.

-Proteins are embedded in the cell membrane. - used for transport - used for receptors

Cell membranes also have cholesterol molecules imbedded in the phospholipid layer that give flexibililty and strength to the cell.

The entire cell membrane is a fluid and thus is called a FLUID MOSAIC model. http://www.susanahalpine.com/anim/Life/memb.htm A mosaic is a picture made of different pieces.

Carbohydrates may be attached to the proteins and lipids and are used for: Identification of cells (ID) Cell to cell adhesion

Carbohydrates Glycoprotein Phospholipids cholesterol Cholesterol Cytoskeleton Cholesterol Receptor protein Transport protein

Chemical signals are transmitted across the cell membrane. Receptors bind with ligands and change shape. Ligands are the molecules that bind to the receptors.

There are two types of receptors. intracellular receptor membrane receptor

Intracellular receptors face inside of the cell Intracellular receptors face inside of the cell. The ligand passes through the membrane and binds to the receptor. Some hormones are like this. Membrane receptors bind to ligands outside of the cell. This causes a change in the protein and transmits the message to the cell.

RBC’s have membrane receptors used to signal the pick up of O2.

Phospholipids carbohydrates

The entire cell membrane is fluid so the structure is referred to as a fluid mosaic model. http://www.susanahalpine.com/anim/Life/memb.htm http://telstar.ote.cmu.edu/biology/MembranePage/index2.html

The membrane is flexible, not rigid The phospholipids can glide and move. The different parts are like a mosaic picture. http://www.susanahalpine.com/anim/Life/memb.htm

Moving molecules in and out of cells….. Cell membranes are semipermeable; they allow certain molecules to move in or out.

What controls what goes into or out of the cell? The size of the molecule 2) The type of molecule Oxygen, CO2, H2O (through pores) pass easily. Lipids and non polar molecules pass. Polar molecules such as glucose don’t. 3) The concentration of the molecule

How do molecules move into and out of cells? Passive transport - no energy required Active transport - energy required

TYPES OF PASSIVE TRANSPORT Diffusion Osmosis Facilitated Diffusion

DIFFUSION Definition: Movement of molecules from high to low concentration When the concentration is the same everywhere, equilibrium is reached.

http://www.indiana.edu/~phys215/lecture/lecnotes/lecgraphics/diffusion.gif

Diffusion will continue until an equilibrium is reached.

Molecules diffuse DOWN their concentration gradients.

FACILITATED DIFFUSION: Transport Proteins facilitate the diffusion of glucose (or other molecules) across the membrane. 100’s exist – allows salts, sugars, … to cross membranes faster.

Transport Proteins

OSMOSIS Definition: Movement of WATER across a semi-permeable membrane - Water moves from an area of low solute HYPOTONIC concentration to an area of high solute HYPERTONIC concentration until equilibrium is reached.

ISO ISO HYPO HYPER HYPERTONIC – more solute HYPOTONIC – less solute ISOTONIC – same solute on both sides ISO ISO HYPO HYPER

WATER ALWAYS MOVES INTO A HYPERTONIC SOLUTION! This causes aquatic small animals to take on water. They have to pump it out with a contractile vacuole.

Contractile vacuole

TURGIDITY in plants If you put cells in pure water HYPOTONIC, they will take on water and possibly bust unless it is a plant cell and they will become TURGID.

If you put cells in a salt water, HYPERTONIC environment, they will lose water. This is called plasmolysis.

Plasmolysis Notice the cell membrane pulls away from the cell wall.

Can you explain this? Plain Water Salt Water

Our blood cells have to be closely regulated as to their surrounding fluid. hypotonic isotonic hypertonic

IV fluids have to be isotonic to your blood plasma to prevent damage to your blood cells.

Which way will water move? 5% NaCl 0.9% NaCl 5% NaCl

What can you say about the concentration of the solution in the beaker based on the results shown in the diagram?   Beaker one has the most concentrated solution. Beaker 2 is isotonic. Beaker 3 has the least concentrated solution. More water moves in the most concentrated area. Tap Water 2% Starch Solution 4% Starch Solution

A U-tube is divided into 2 halves, A and B, by a membrane which is freely permeable to water and salt, but NOT to glucose. Side A is filled with a solution of 8% salt and 2% glucose, while side B is filled with 2% salt and 8% glucose. Where does the salt flow? The water? salt salt 8% Salt 2% Glucose Side A 2% Salt 8% Glucose Side B water Since glucose cannot move, the higher solute is on the right side.

ACTIVE TRANSPORT DEFINITION: movement from low to high concentration Types: PROTEIN PUMPS ENDOCYTOSIS EXOCYTOSIS Takes ENERGY

Protein pumps are used to pump ions against the concentration gradient.

ENDOCYTOSIS Definition: Taking material in by infoldings or pockets of the cell membrane Two Types: Phagocytosis: “cell eating” ; cytoplasm engulfs large particles (typically food) http://academic.brooklyn.cuny.edu/biology/bio4fv/page/phago.htm 2. Pinocytosis: “cell drinking”; liquid http://academic.brooklyn.cuny.edu/biology/bio4fv/page/endocytb.htm

EXOCYTOSIS Definition: removal of large amounts of material (waste particles) A vacuole forms with the material to leave; fuses with the cell membrane and forces the contents out of the cell http://academic.brooklyn.cuny.edu/biology/bio4fv/page/exocy.htm

Salt “sucks” out the water!

Investigating Cell Membranes

What is outside the tubing? Remember that iodine turns starch dark blue/black.

How do we test for glucose? Glucose Test Strips

Modeling the membrane