SELECTIVELY PERMEABLESELECTIVELY PERMEABLE: Controls what comes in and outin and out of the cell. Does not let largelarge, chargedcharged or polarpolar things through without help.

FLUID MOSAIC MODELFLUID MOSAIC MODEL: The phospholipids movephospholipids move, thus allowing small non-polar molecules to slip through.

GLYCOLIPIDS and GLYCOPROTEINSGLYCOLIPIDS and GLYCOPROTEINS: Act as receptorsreceptors – receive info. from body to tell cell what to do.

INTEGRAL PROTEINSINTEGRAL PROTEINS: assistsassists specific larger and charged molecules to move in and outmolecules to move in and out of the cell. Can act as ‘tunnels’ or will change shape.

CHOLESTEROLCHOLESTEROL: ReducesReduces membrane fluidityfluidity by reducing phospholipid movement. Also stops the membrane from becoming solidsolid at room temperatures.

CYTOSKELETONCYTOSKELETON: A cytoskeleton acts as a framework that gives the cell it's shapegives the cell it's shape. It also serves as a monorail to transporttransport organelles around the cell.

1. Passive transport moves molecules from a [high][high] to [low][low] in order to establish equilibrium.

The molecules may or may not need to use a proteinprotein channel or carrier.

Everything that is transported across the cell membrane takes place by one of two fundamental processes:

2. Active transport moves molecules from [low][low] to [high][high], AGAINSTAGAINST the concentration gradient and this process requires energyenergy in the form of ATP.

Simple DiffusionSimple Diffusion is a passivepassive process ( nono energy required).

Some substances will diffuse through membranes as if the membranes weren’t even there.

Molecules diffuse until they are evenlyevenly distributed.

The molecules move from an area of [high] to [low].[high] to [low].

EXAMPLES of molecules that easily cross cell membranes by simple diffusion are: oxygen, carbon dioxide, alcohols, oxygen, carbon dioxide, alcohols, fatty acids, glycerol, and ureafatty acids, glycerol, and urea.

Alcohol & Urea

Fatty Acids, Glycerol,

The rate of diffusion will be increased when there is :

1.1. ConcentrationConcentration: the difference in [ ] between two areas (the [ ] gradient) causes diffusion. The greater the greater the difference in concentration,difference in concentration, the fasterfaster the diffusion.

2.2. Molecular sizeMolecular size: smaller substances diffuse more quickly.quickly. Large molecules (such as starches and proteins) simply cannot diffuse through.

3. Shape of Ion/MoleculeShape of Ion/Molecule: a substance’s shape may preventprevent it from diffusing rapidly, where others may have a shape that aids their diffusion.

4. 4. Viscosity of the MediumViscosity of the Medium: the lower the viscosity, the more slowlyslowly molecules can move through it.

5.5. Movement of the MediumMovement of the Medium: currents will aid diffusion. Like the wind in air, cytoplasmic steamingcytoplasmic steaming (constant movement of the cytoplasm) will aid diffusion in the cell.

6.6. SolubilitySolubility:: lipidlipid - soluble molecules will dissolve through the phospholipid bilayer easily,easily, as will gases like CO2 and O2.

7. PolarityPolarity: waterwater will diffuse, but because of its polarity, it will

notnot pass through the non-polar phospholipids. Instead, water passes though specialized protein ionprotein ion channels.

OsmosisOsmosis is the diffusiondiffusion of waterof water across a selectively permeable membrane driven by a difference in the difference in the concentration of solutesconcentration of solutes on the two sides of the membrane.

A selectively permeable membrane is one that allows unrestricted passage of waterwater, but not solute molecules or ions.

So it is the WATER THAT WATER THAT MOVESMOVES to create equilibrium!!!

• Osmosis requires NONO ENERGY.

• Osmosis is the net movement of WATERWATER molecules from the area of [high][high] of water to the area of [low][low] of water until it is equally equally distributed.distributed.

• Because membranes often restrict or preventrestrict or prevent the movement of some molecules, particularly large ones, the water (solventsolvent) must be the one to move.move.

•To cross the membrane, water must move through a protein ion channelprotein ion channel.

•In certain cellular conditions, these protein channels can be opened or closed (ie: in the kidneyskidneys, large large intestinesintestines) depending on how much water is needed by the body.

ISOTONIC SOLUTIONISOTONIC SOLUTION:

1. the solution concentration is equalequal on both sides of the membrane .

2. There is no net concentration difference across the cell membrane

3. Water moves back and forth, but there is no net gain or no net gain or lossloss of water.

The tonicity of a solution will affect the size & shape of cells:

HYPERTONIC SOLUTIONHYPERTONIC SOLUTION:

1. The solution outsideoutside the cell is more concentrated than inside.

2. There is more water inside the cell and the water will move outout of the cell.

3. This causes the cell to shrinkshrink

4.4. *Memory Trick...*Memory Trick... Hyper people get skinny!

HYPOTONIC SOLUTIONHYPOTONIC SOLUTION: 1. The concentration insideinside the

cell is more concentrated than outside.

2. Therefore there is more water outside of the cell, and water will move intointo the cell.

3. This will cause the cell to swellswell..

4.4. *Memory Trick...*Memory Trick... Hippos are FAT!

In Biology we usually talk about the SOLUTION’S tonicity, NOT the cells!

When we speak of plants, we speak of TURGOR PRESSURETURGOR PRESSURE.

Which of these cells is in a hypertonic solution? Hypotonic?

Facilitated TransportFacilitated Transport: Some molecules are notnot normally able to pass through the lipid membrane, and need channel or carrierchannel or carrier proteinsproteins to help them move across.

This does notnot require energyrequire energy when moving from [H] to [L] (with the concentration gradient).

Molecules that need help to move through the plasma membrane are either charged, polar, charged, polar, or too large or too large..

If molecules are POLAR, CHARGED, or TOO LARGE they need a protein the help them across the membrane

EXAMPLES: sugars, amino acids, ions, nucleotidessugars, amino acids, ions, nucleotides ….

Each protein channel or protein carrier will allow only ONE TYPE ONE TYPE OF MOLECULEOF MOLECULE to pass through it.

Many channels contain a “gate”“gate” which control the channel's permeability.

When the gate is open, the channel transports, and when the gate is closed, the channel is closed.

These gates are extremely important in the nervenerve cells.

Active TransportActive Transport: the movement of polar, large, and charged molecules moving againstagainst the [ ] gradient (uphilluphill).

EXAMPLES of molecules that move this way are all of the things that require protein carriers to move across the plasma membrane.

ionsions (like Na+ and K+ in cells, and iodine) and sugarssugars, amino acidsamino acids, nucleotidesnucleotides...

Example 1: the thyroid gland accumulates iodine as it is needed to manufacture the hormone thyroxin.

The iodine concentration can be as much as 25 times more concentrated in the thyroid than in blood.

Example 2: a Na/K pump (mostly in nerve membranes). These function to restore electrical order in a nerve after an impulse has traveled along it.

Example 3: In order to make ATP in the mitochondria, a proton pump (hydrogen ion) is required.

EndocytosisEndocytosis: (“Endo” means “in”“in”).

Endocytosis is the taking in of molecules or particles by invaginationinvagination of the cell membrane forming a vesicle.

This requires energy.requires energy.

There are two types of endocytosis:

1. pinocytosispinocytosis (cell drinking): small molecules are ingested and a vesicle is immediately formed. This is seen in small intestinesmall intestine cells (villi)

2. phagocytosisphagocytosis (cell eating): large particles, (visible with light microscope) are invaginated into the cell (ie: white white blood cells ‘eat’ bacteriablood cells ‘eat’ bacteria).

ExocytosisExocytosis: (“Exo” means “out”“out”.)

•Exocytosis is the reversereverse of endocytosis.

•This is where a cell releases the releases the contentscontents of a vesicle outside of the cell.

•These contents may be wastes, proteins, hormoneswastes, proteins, hormones, or some other product for secretion.

•This also requires energy.requires energy.

•Example: vesicles from the GolgiGolgi fuse with the plasma membrane and the proteins are released outside of the cell.