Membrane Transport

Cell or Plasma Membrane Composed of double layer of phospholipids and proteins (phospholipid bilayer) Surrounds outside of ALL cells Controls what enters or leaves the cell Living layer Outside of cell Inside (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains copyright cmassengale

copyright cmassengale Phospholipids Heads contain glycerol & phosphate and are hydrophilic (attract water) Tails are made of fatty acids and are hydrophobic (repel water) Make up a bilayer where tails point inward toward each other Can move laterally to allow small molecules (O2, CO2, & H2O to enter) copyright cmassengale

Cell Membrane Proteins Proteins help move large molecules or aid in cell recognition Peripheral proteins are attached on the surface (inner or outer) Integral proteins are embedded completely through the membrane copyright cmassengale

The Cell Membrane is also referred to as the Fluid Mosaic Model Molecules in cell membranes are constantly moving and changing copyright cmassengale

Structures Of The Plasma Membrane Phosphate Head: Made of a phosphate group (polar and attracts water) Carbohydrate: Used for cell recognition Membrane Protein: Transports large particles across the cell membrane Cholesteral: Helps stabilize the phospholipids Lipid Tails: Made of fatty acids (non-polar and does not attract water)

Diffusion Movement of particles From high To Low

Diffusion Concentration: the mass of solute (what's being dissolved) in a given volume of solvent (what’s doing the dissolving) Equilibrium: the concentration throughout a solution is the same

Diffusion ● Concentration gradient: the difference in concentration across a barrier/membrane ● Because diffusion depends upon random particle movements, substances diffuse across membranes without requiring the cell to use energy

Osmosis Movement of water From high to low Across a selectively permeable membrane -selects what moves in and out

Osmosis

Dynamic Equilibrium Equal concentrations are reached Not the same volumes Continued movement across the membrane Not gain or loss

Osmosis ● Osmosis is the diffusion of water through a selectively permeable barrier. Water will tend to move across the membrane until equilibrium is reached, when this occurs the two solutions will be isotonic, the same. ● When a solution is more concentrated with solute it is said to be hypertonic, whereas a dilute (less concentrated) solution is said to be hypotonic. Pre-AP do the potato experiment with salt water Discuss osmotic pressure as a side discussion to the second question. For Pre AP may wish to perform potato lab with regular tap water and salt water.

Osmosis

Isotonic Solutions Iso- equal No change in concentrations Water still moves Same amount of water moves in as moves out Both sides of membrane are the same

Hypertonic Solution Hyper- Over Out side of cell More dissolved substance Less water Water moves out of cell

Hypotonic Solution Hypo- under Out side of cell Water moves into cell Less dissolved substance More water Water moves into cell

Passive Transport Cell uses no energy From high to low Plasma membrane Concentration gradient

Facilitated Diffusion Type of passive transport Use transport proteins Channel proteins Carrier proteins Changes shape From high to low

Facilitated Diffusion ● During facilitated diffusion molecules that would not normally be able to cross through the membrane, such as glucose, diffuse across the membrane through selected protein channels. It is dependent upon the concentration gradient because it does not require the cell to expend any energy.

Active Transport Cell uses energy Against concentration gradient From low to high Carrier Proteins Molecule binds with carrier protein Energy then used to change shape Molecule released on other side Carrier protein returns to original shape

Active Transport ●The movement of material across a membrane and against a concentration gradient is called active transport. Like facilitated diffusion this is carried out by protein channels in the membrane called transport proteins, however in this form of diffusion energy is expended in the process of “pumping” the material “uphill” against the gradient.

Active Transport Molecule to be carried Molecule being carried Energy

Large Particle Transport ● Endocytosis is the process of taking material into the cell by means of enfolding's, or pockets, of the cell membrane. The pocket or enfold, once it has surrounded the molecule, then closes and breaks off from the membrane forming a vacuole. Two examples of endocytosis are phagocytosis (cell eating) and pinocytosis (cell drinking). ● Exocytosis works the opposite of endocytosis. It is a vacuole with material designated to leave the cell which joins with the cell membrane then releases its material outside of the cell.

Large Particle Transport (Exocytosis and Endocytosis)

Large Particle Transport Not through membrane Requires energy Exocytosis- out

Large Particle Transport Endocytosis- in

Types of Endocytosis Pinocytosis: liquid (into) Phagocytosis: Solid (into)