PRESCRIBED LEARNING OUTCOMES PRESCRIBED LEARNING OUTCOMES (Chapter 4, pp. 65-76) G1. Apply knowledge of organic molecules to explain the structure and function of the fluid-mosaic model G2. Explain why the cell membrane is described as “selectively permeable” G3. Compare and contrast the following: diffusion, facilitated transport, osmosis, and active transport. G4. Explain factors that affect the rate of diffusion across a cell membrane. G5. Describe endocytosis, including phagocytosis and pinocytosis, and contrast it with exocytosis. G6. Predict the effects of hypertonic, isotonic, and hypotonic environments on animal cells G7. Demonstrate an understanding of the relationship and significance of surface area to volume, with reference to cell size.
SELECTIVELY PERMEABLE in and out largechargedpolar SELECTIVELY PERMEABLE: Controls what comes in and out of the cell. Does not let large, charged or polar things through without help.
FLUID MOSAIC MODELphospholipids move FLUID MOSAIC MODEL: The phospholipids move, thus allowing small non-polar molecules to slip through.
GLYCOLIPIDS and GLYCOPROTEINS receptors GLYCOLIPIDS and GLYCOPROTEINS: Act as receptors – receive info. from body to tell cell what to do.
INTEGRAL PROTEINSassists molecules to move in and out INTEGRAL PROTEINS: assists specific larger and charged molecules to move in and out of the cell. Can act as ‘tunnels’ or will change shape.
CHOLESTEROLReduces fluidity solid CHOLESTEROL: Reduces membrane fluidity by reducing phospholipid movement. Also stops the membrane from becoming solid at room temperatures.
CYTOSKELETON gives the cell it's shape transport CYTOSKELETON: A cytoskeleton acts as a framework that gives the cell it's shape. It also serves as a monorail to transport organelles around the cell.
[high] [low] 1.Passive transport moves molecules from a [high] to [low] in order to establish equilibrium. protein The molecules may or may not need to use a protein channel or carrier. Everything that is transported across the cell membrane takes place by one of two fundamental processes:
Simple Diffusionpassiveno Simple Diffusion is a passive process ( no energy required). Some substances will diffuse through membranes as if the membranes weren’t even there. evenly Molecules diffuse until they are evenly distributed. [high] to [low]. The molecules move from an area of [high] to [low]. oxygen, carbon dioxide, alcohols, fatty acids, glycerol, and urea EXAMPLES of molecules that easily cross cell membranes by simple diffusion are: oxygen, carbon dioxide, alcohols, fatty acids, glycerol, and urea.
The rate of diffusion will be increased when there is : 1.Concentration greater the difference in concentration,faster 1.Concentration: the difference in [ ] between two areas (the [ ] gradient) causes diffusion. The greater the difference in concentration, the faster the diffusion. 2.Molecular sizequickly. 2.Molecular size: smaller substances diffuse more quickly. Large molecules (such as starches and proteins) simply cannot diffuse through. Shape of Ion/Moleculeprevent 3. Shape of Ion/Molecule: a substance’s shape may prevent it from diffusing rapidly, where others may have a shape that aids their diffusion.
4. Viscosity of the Medium slowly 4. Viscosity of the Medium: the lower the viscosity, the more slowly molecules can move through it. 5. Movement of the Medium cytoplasmic steaming 5. Movement of the Medium: currents will aid diffusion. Like the wind in air, cytoplasmic steaming (constant movement of the cytoplasm) will aid diffusion in the cell. 6.Solubility:lipid easily, 6.Solubility: lipid - soluble molecules will dissolve through the phospholipid bilayer easily, as will gases like CO 2 and O 2. Polaritywater not protein ion 7. Polarity: water will diffuse, but because of its polarity, it will not pass through the non-polar phospholipids. Instead, water passes though specialized protein ion channels.
Osmosisdiffusionof water difference in the concentration of solutes Osmosis is the diffusion of water across a selectively permeable membrane driven by a difference in the concentration of solutes on the two sides of the membrane. water A selectively permeable membrane is one that allows unrestricted passage of water, but not solute molecules or ions. WATER THAT MOVES So it is the WATER THAT MOVES to create equilibrium!!!
NOOsmosis requires NO ENERGY. WATER [high] [low]equally distributed.Osmosis is the net movement of WATER molecules from the area of [high] of water to the area of [low] of water until it is equally distributed. restrict or prevent solvent move.Because membranes often restrict or prevent the movement of some molecules, particularly large ones, the water (solvent) must be the one to move.
protein ion channelTo cross the membrane, water must move through a protein ion channel. kidneyslarge intestinesIn certain cellular conditions, these protein channels can be opened or closed (ie: in the kidneys, large intestines) depending on how much water is needed by the body.
ISOTONIC SOLUTION ISOTONIC SOLUTION: equal 1.the solution concentration is equal on both sides of the membrane. 2.There is no net concentration difference across the cell membrane no net gain or loss 3.Water moves back and forth, but there is no net gain or loss of water. The tonicity of a solution will affect the size & shape of cells:
HYPERTONIC SOLUTION HYPERTONIC SOLUTION: outside 1.The solution outside the cell is more concentrated than inside. out 2.There is more water inside the cell and the water will move out of the cell. shrink 3.This causes the cell to shrink 4.*Memory Trick... 4.*Memory Trick... Hyper people get skinny!
HYPOTONIC SOLUTION HYPOTONIC SOLUTION: inside 1.The concentration inside the cell is more concentrated than outside. into 2.Therefore there is more water outside of the cell, and water will move into the cell. swell. 3.This will cause the cell to swell. 4.*Memory Trick... 4.*Memory Trick... Hippos are FAT!
Facilitated Transportnot channel or carrierproteins Facilitated Transport: Some molecules are not normally able to pass through the lipid membrane, and need channel or carrier proteins to help them move across. notrequire energy This does not require energy when moving from [H] to [L] (with the concentration gradient). charged, polar, or too large. Molecules that need help to move through the plasma membrane are either charged, polar, or too large.
If molecules are POLAR, CHARGED, or TOO LARGE they need a protein the help them across the membrane sugars, amino acids, ions, nucleotides EXAMPLES: sugars, amino acids, ions, nucleotides ….
ONE TYPE OF MOLECULE Each protein channel or protein carrier will allow only ONE TYPE OF MOLECULE to pass through it.
“gate” Many channels contain a “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. nerve These gates are extremely important in the nerve cells.
Active Transport against uphill Active Transport: the movement of polar, large, and charged molecules moving against the [ ] gradient (uphill). EXAMPLES of molecules that move this way are all of the things that require protein carriers to move across the plasma membrane. ions sugarsamino acids nucleotides ions (like Na+ and K+ in cells, and iodine) and sugars, amino acids, nucleotides...
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.
Endocytosis“in” Endocytosis: (“Endo” means “in”). invagination Endocytosis is the taking in of molecules or particles by invagination of the cell membrane forming a vesicle. requires energy. This requires energy.
There are two types of endocytosis: pinocytosis small intestine 1. pinocytosis (cell drinking): small molecules are ingested and a vesicle is immediately formed. This is seen in small intestine cells (villi) phagocytosis white blood cells ‘eat’ bacteria 2. phagocytosis (cell eating): large particles, (visible with light microscope) are invaginated into the cell (ie: white blood cells ‘eat’ bacteria).
Exocytosis“out” Exocytosis: (“Exo” means “out”.) reverseExocytosis is the reverse of endocytosis. releases the contentsThis is where a cell releases the contents of a vesicle outside of the cell. wastes, proteins, hormonesThese contents may be wastes, proteins, hormones, or some other product for secretion. requires energy.This also requires energy. GolgiExample: vesicles from the Golgi fuse with the plasma membrane and the proteins are released outside of the cell.
Cells exist individually, or in groups forming tissues, organs, and eventually organisms. size Their size is a very important factor for their survival. function effectively Cells are the size they are because that is the size they have to be in order to function effectively. needs to usewastes The materials it needs to use, and the wastes it needs to remove must pass in and out of the cell through the cell membrane.
volume increasing faster As a cell grows, it suffers the possibility of the volume increasing faster than the surface area. more it needs The bigger the cell, the more it needs and the more it needs to get rid of. too bignot be enough room membrane If the cell gets too big, there will not be enough room on the plasma membrane for things to get in and out quickly enough to maintain the cell. Why? Its surface area has not kept up to its volume size. surface area does not increase in the same proportion When the volume of a cell increases, the amount of surface area does not increase in the same proportion.
divide When cells grow larger, if they don’t want to die, the only real solution is to divide. increase Once a cell has divided, the surface area to volume ratio will increase and the problem is solved.
*When you see questions regarding surface area to volume ratio, think of a water balloon. (ie: when you squish a water balloon, it has the same volume, but the surface area is increased!)