Cellular Membrane and Transport GT Biology

Cell Membrane & Transport Introduction In order to live, a cell must take in nutrients and water and eliminate wastes Parts of the cell involved in diffusion and osmosis: 1. The cytoplasm 2. The cell membrane

1. Cytoplasm – the jelly-like substance composed of mainly water and dissolved solutes. It is the matrix which contains all of the cellular organelles enclosed by the cell membrane.

2. Cell membrane – a semipermeable membrane that allows some small molecules through, but blocks others.

Structure and Function of The Cell Membrane Protect animal cells; the outer most layer 2. Control the movement of substances into and out of the cell 3. Contains molecules for cell identity and recognition

Structure 1. Phospholipids- Molecules that are made of a phosphate group and two fatty acid (lipid) chains. * Phophate is the “head” and is polar or hydrophillic (likes water)

Two fatty acid chains attached to the phosphate groups they are the “tail” and are hydrophobic (water hating)

These two molecules align side by side with the phosphates oriented toward the outside and inside of the and the lipids toward each other. WHY? Phosphates are attracted to water and lipids to other lipids

Outside cell Phosphate heads water No water Lipid tails water Phosphates heads Inside cell

Selective Permeability animation

This forms the BILAYER ( double layer) all the way around the cell.

2. Cholesterol Lipid molecules needed to keep the bilayer rigid yet stable.

3. Proteins Proteins imbedded in the membrane for various functions: * enzymes ( catalyst for reactions) * transport channels ( to allow substances to cross) *receptors (attachment of various molecules that may enter the cell or initiate a reaction) * Protiens with carbohydrates attached for Cell and self identification

The structure of the cell membrane has a special name….. The Fluid- Mosaic Model Why? Fluid = fluid-like movement, maleable like a water balloon, not like a ping- pong ball. Mosaic= a combination of many shapes and sizes of molecules like an art mosaic.

Cell membrane structure animation http://www.johnkyrk.com/cellmembrane.html

Journal Entry Explain how the cell membrane came to be a “Bi-layer”. In your paragraph, explain what “bilayer” means.

The movement of Various Substances Into and Out of Cells Substances move into and out of the cell by means of several methods. Some methods require cellular energy while others do not. A. Passive transport: no energy required B. Active Transport: energy required

A. Passive Transport 1. Diffusion is the movement of molecules from an area of greater concentration to an area of lesser concentration. ( with the “flow”) *Diffusion stops when equilibrium (balance) is reached

Low concentration High concentration

Diffusion causes the molecules to move from area A to area B ( allows some things to move across…some are too large and can’t pass through)

Diffusion causes the molecules to move from an area of high concentration to an area of low concentration until all are spread out equally… dynamic equilibrium

Diffusion/Osmosis animation http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html Protein Channels http://www.stolaf.edu/people/giannini/flashanimat/transport/channel.swf

2. Osmosis is the diffusion of water across the cell membrane. * The water will move from an area of low solute to an area of high solute until equilibrium is reached. (The water wants to evenly dilute the solute)

In osmosis, the water will move towards the solute to dilute it evenly.

Osmosis

3. Diffusion and Osmosis Types of solutions Hypertonic – the concentration of solutes outside the cell is greater than it is inside. 1. Water will move outside the cell to dilute the higher concentration of solutes 2. The cell will shrink

Hypertonic Solution 15% salt 85% water 1% salt 99% water

Plant cell The cell wall does not move. The membrane shrinks in and pulls all cell parts in= plasmolysis Animal cell

Hypotonic – the concentration of solutes inside the cell is greater than it is outside 1. Water will move inside the cell to dilute the higher concentration of solutes 2. The cell will SWELL (unless the water is pumped out by a contractile vacuole) – if not it may burst which is called cytolysis

Hypotonic solution 1% salt 99 water 15% salt 85% water

Plant cell Cell fills with water and the wall will be forced to push out= turgid Animal cell

The contractile vacuole in single celled organisms pumps out excess water so the cell does not burst Animation http://www.stolaf.edu/people/giannini/movies.html

Isotonic – the concentration of solutes inside and outside the cell is the same 1. Water will not move 2. The cell will stay the same

Isotonic solution

4. Facilitative diffusion Diffusion where molecules must pass through a protein to get across the cell membrane. ( still movement from high concentration to low)

Facilitative Diffusion animation http://www.d.umn.edu/~sdowning/Membranes/diffusionanimation.html

B. Active Transport Transport of molecules against the concentration gradient, from low concentration to high…against the “flow”

Because movement is AGAINT the flow, the cell must use energy ( ATP is the abbreviation for chemical cellular energy) ATP is used to “power” proteins to pump molecules across, forcing them to go Against the gradient.

Example: Sodium – Potassium Pump The cell wants to keep low sodium in and high potassium in. It must utilize active transport to pump sodium out and potassium in to keep these levels. Sodium-potassium pump animation http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/ion_pump/ionpump.html

Journal Entry What would happen if you took your goldfish (freshwater fish) to Ocean City for the summer and decided to let it go in the ocean? Explain in terms of osmosis, hypertonic, hypotonic and such. 2. You decide to take the baby shark you caught in Ocean City and put it in your swimming pool. Explain as above. 3. Compare active and passive transport using a Venn diagram.