Cell MembraneCell Membrane The composition of nearly all cell

membranes is a double-layered sheet called a lipid bilayer. The phospholipid bilayer gives cell membranes a flexible structure that forms a strong barrier between the cell and its surroundings. The cell membrane regulates what enters and leaves the cell and also provides the cell with protection and support.

Structure of Cell Structure of Cell MembraneMembrane

Has a phospholipid bilayer (2 layers Has a phospholipid bilayer (2 layers of fat).of fat).

The Cell MembraneThe Cell Membrane

Maintains Maintains homeostasishomeostasis for the for the cell by allowing waste and other cell by allowing waste and other products to leave the cell.products to leave the cell.

Selectively Permeable – allows Selectively Permeable – allows only some materials in and out of only some materials in and out of the cell.the cell.

Water and oxygen move freely Water and oxygen move freely across the cell's membrane.across the cell's membrane.

The phospholipids have a:The phospholipids have a:– hydrophilic head (water loving)hydrophilic head (water loving)– two hydrophobic tails (water fearing)two hydrophobic tails (water fearing)

Cell MembraneCell Membrane

The Cell Membrane is also called The Cell Membrane is also called ““The Fluid Mosaic Model”The Fluid Mosaic Model”

– Because the membrane is flexible Because the membrane is flexible and the lipids move within the and the lipids move within the membrane. membrane. (like water molecules (like water molecules move in the currents of a lake).move in the currents of a lake).

– Also because proteins create a Also because proteins create a “mosaic” or pattern on the surface “mosaic” or pattern on the surface of the membrane.of the membrane.

Another type of lipid in the cell membrane is Another type of lipid in the cell membrane is CHOLESTEROL that makes the membrane more fluid. CHOLESTEROL that makes the membrane more fluid.

Embedded in the phospholipid bilayer are PROTEINS that Embedded in the phospholipid bilayer are PROTEINS that also aid in diffusion and in cell recognition. also aid in diffusion and in cell recognition.

Proteins called INTEGRAL proteins go all the way through Proteins called INTEGRAL proteins go all the way through the bilayer, while PERIPHERAL proteins are only on one the bilayer, while PERIPHERAL proteins are only on one side. side.

Large molecules like PROTEINS or carbohydrates use Large molecules like PROTEINS or carbohydrates use proteins to help move across cell membranes. proteins to help move across cell membranes.

Some of the membrane proteins have carbohydrate Some of the membrane proteins have carbohydrate chains attached to help cells in recognize each other and chains attached to help cells in recognize each other and certain moleculescertain molecules

Passive Transport- Passive Transport- moving molecules across moving molecules across

cell membranecell membrane Does NOT require energyDoes NOT require energy.. Three Types:Three Types:

– DiffusionDiffusion– OsmosisOsmosis– Facilitated DiffusionFacilitated Diffusion

DiffusionDiffusion

As a result, the particles tend to move from an area of greater concentration to an area of lower concentration.

EQUILIBRIUM- when the molecules are EQUILIBRIUM- when the molecules are even throughout a space.even throughout a space.

Diffusion depends upon random particle movements, across membranes without requiring extra energy

http://www.youtube.com/watch?v=E7kor5nHtZQ&feature=endscreen&NR=1

Facilitated DiffusionFacilitated Diffusion Movement of large molecules across the cell Movement of large molecules across the cell

membrane using PROTEINS!!membrane using PROTEINS!! Cell membranes have transport proteins

that act as carriers, making it easy for certain molecules to cross.

Each channel is specific for 1 type of molecule

facilitating, or helping, the diffusion of molecules across the membrane, and this is called facilitated diffusion.

OsmosisOsmosis The movement of WATER across the The movement of WATER across the

cell membrane from high cell membrane from high concentration to low concentrationconcentration to low concentration..

Huddle UpHuddle Up

1.1. What part of the cell membrane is What part of the cell membrane is hydrophilic? What part is hydrophilic? What part is hydrophobic?hydrophobic?

2.2. What is diffusion?What is diffusion?

3.3. What is osmosis?What is osmosis?

Three Types of Three Types of SolutionsSolutionsIsotonicIsotonicHypotonicHypotonicHypertonicHypertonic

– Recall a Solution = Solute + SolventRecall a Solution = Solute + Solvent– Solute – substance being dissolvedSolute – substance being dissolved– -Solvent – substance that does the dissolving-Solvent – substance that does the dissolving

http://www.youtube.com/watch?v=nd2jtwviyC8&feature=related

Isotonic Solution- Isotonic Solution- “ISO” means same“ISO” means same

If the concentration of solute If the concentration of solute (salt) is equal on both sides, (salt) is equal on both sides, the water will move back and the water will move back and forth equally.forth equally.

Hypotonic Solution- Hypotonic Solution- “HYPO” means less“HYPO” means less

There are less solute (salt) molecules in There are less solute (salt) molecules in the solution so water will move into the the solution so water will move into the cell.cell.

Cell gets larger and could burst and die.Cell gets larger and could burst and die.In plant cells, the central vacuoles In plant cells, the central vacuoles will fill and the plant becomes stiff will fill and the plant becomes stiff and rigid, the cell wall keeps the and rigid, the cell wall keeps the plant from bursting.plant from bursting.

In animal cells, the cell may In animal cells, the cell may be in danger of bursting, be in danger of bursting, organelles called organelles called CONTRACTILE CONTRACTILE VACUOLESVACUOLES will pump water out of the cell to prevent this.will pump water out of the cell to prevent this.

http://www.youtube.com/watch?v=N8hAwVaaD84

Hypertonic Solution- Hypertonic Solution- “Hyper” means more“Hyper” means more There are more solute (salt) There are more solute (salt)

molecules in the solution, so the molecules in the solution, so the water is sucked out of the cell.water is sucked out of the cell.

Cell shrinks, Cell shrinks,

causes cell to die. causes cell to die.

Osmotic PressureOsmotic Pressure

For organisms to survive, they must have a way to balance the intake and loss of water.

Can Drinking Salt Can Drinking Salt Water Hurt You?Water Hurt You? Yes! This is why it is dangerous to drink Yes! This is why it is dangerous to drink

sea water.sea water. Its a myth that drinking sea water will Its a myth that drinking sea water will

cause you to go insane, but people cause you to go insane, but people marooned at sea will speed up marooned at sea will speed up dehydration (and death) by drinking sea dehydration (and death) by drinking sea water. water.

This is also why "salting fields" was a This is also why "salting fields" was a common tactic during war. It would kill common tactic during war. It would kill the crops in the field, thus causing food the crops in the field, thus causing food shortages.shortages.

Active TransportActive Transport

REQUIRES ENERGY REQUIRES ENERGY b/c b/c materials are moving against the materials are moving against the concentration gradient.concentration gradient.

Molecules from an area of Molecules from an area of LOW concentration to HIGH LOW concentration to HIGH concentration.concentration.

Active TransportActive Transport

The active transport of small molecules or ions across a cell membrane is generally carried out by transport proteins or “pumps” that are found in the membrane itself.

Larger molecules and clumps of material can also be actively transported across the cell membrane by processes known as endocytosis and exocytosis.

Types of Active Types of Active TransportTransport

Endocytosis- moving large Endocytosis- moving large particles INTO the cell by the cell particles INTO the cell by the cell membrane engulfing them.membrane engulfing them.– Phagocytosis: engulf large FOOD Phagocytosis: engulf large FOOD

particlesparticles– Pinocytosis: engulf large LIQUID Pinocytosis: engulf large LIQUID

particlesparticles Exocytosis – moving large Exocytosis – moving large

particles OUT of the cell.particles OUT of the cell.

Endocytosis (en-doh-sy-TOH-sis) is the process of taking material into the cell by means of infoldings, or pockets, of the cell membrane.

Phagocytosis means “cell eating.” In phagocytosis, extensions of cytoplasm surround a particle and package it within a food vacuole. The cell then engulfs and digests it.

Exocytosis (ek-soh-sy-TOH-sis) is the process by which cells release large amounts of material from the cell.