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41 Cards in this Set
- Front
- Back
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Fluid Mosaic Model
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* shows proteins embedded in a fluid lipid bilayer
* mosaic of proteins floating in or on the lipid bilayer * discovered 1972 by Jonathan Singer and Garth Nicolson |
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phospholipids
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composed of glycerol linked to 2 fatty acid tails and a phosphate group
- the head (phosphate group) is hydrophilic (i.e-polar)stick out the bilayer - the tails (fatty acids) are hydrophobic (i.e-nonpolar)float in the middle of the bilayer - the membrane's foundation |
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globular proteins
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- membrane proteins which are not very soluble in water
- possess long stretches on nonpolar hydrophobic amino acids - inserted in the lipid bilayer |
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Cellular Membrane
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- consist of 4 components
1.phospholipid bilayer 2.transmembrane proteins 3.interior protein network 4.cell surface markers |
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phospholipid bilayer
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- is fluid
- 2 layers held together by H-bonding of water - sat. fatty acids make the membrane LESS fluid than unsat. - warm temp makes it LESS fluid also - other components embedded in the bilayer imposes a barrier to permeability - formed spontaneously |
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Transmembrane proteins
(intergral membrane proteins) |
- span the lipid bilayer
- nonpolar regions are embedded in the interior of the bilayer - polar ends protrude from both sides of bilayer -possess at least 1 transmembrane domain - protrude through the plasma membrane |
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Peripheral membrane proteins
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- assosciated w/ the surface of the membrane but not part of its structure
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glycoproteins
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- "self" recognition
- create a protein/carb chain shape characterisitic of individual |
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glycolipid
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- tissue recognition
- create a lipid/carb shape characteristic of tissue - cell surface markers |
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What happens to phospholipids when placed in water?
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Polar head repels the nonpolar tails of the phospholipids.
- forming the phospholipid bilayer |
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Membrane Fluidity
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- affected by chain length, temperature, and pH
(i.e- higher the temp, the LESS fluid) -sat. fats make it LESS fluid -unsat. fats make it MORE fluid (due to "kinks" from double bonds that keep them from packing tightly together) - cholesterol, depending on temp, can either dec or inc fluidity |
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Selective Permeability
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-when a membrane is permeable to some substances and not others
- small or NONPOLAR molecules move across quickly - large or charged ions don't |
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Proteins (6 key classes)
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1. transporters-allowing only certain substances in or out of cell through channels or carriers
2. enzymes- used to carry out chem. rxn on the interior of plasma membrane 3. cell surface receptors- detect chemical messages on surfaces of membranes |
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Proteins cont...
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4. cell surface identity markers- markers that identify them to other cells w/ their own ID type
5. cell-to-cell adhesion proteins- used to glue themselves to one another. good for tissues & organs 6. attachments to cytoskeleton- anchored by linking proteins to interact with others |
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Pores
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-created from extensive nonpolar regions w/in a transmembrane protein
- Beta sheets in the proteins 2nd degree structure. - known as a beta barrel which is formed as a polar environment in the interior |
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2 types of transport
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1. PASSIVE transport (movement down the concen. gradient from high to low)
-diffusion -facilitated diffusion -osmosis 2. ACTIVE transport (requires E; movement against the concen. gradient from low to high) -direct -indirect |
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Diffusion
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- passive transport
- movement of molecules from HIGH concentration to LOW concentration -continues until concent. is the same in all regions -movement in both directions occur but theres NO net movement in either direction - a selective process |
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Channel Proteins
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- have POLAR interior allowing polar (hydrophilic) molecules to pass
- channel must be open to occur - includes ion channels & gated channels - makes the cell membrane selectively permeable - usually involves diffusion |
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Ion channels
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- allows the passing of ions (charged atoms or molecules) which are assossciated with H20
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Gated channels
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- are opened or closed in response to a stimulus (stimulus can be chemical or electrical)
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Carrier Proteins
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-bind to a specific molecule to fascilitate its passage.
- usually involves fascilitated diffusion |
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Facilitated Diffusion
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- movement of a molecule from HIGH to LOW concent. w/ the aid of a carrier protein
-inc. in concent means more of the carriers are bound to the transport molecule |
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In aqueous solution, water is termed the _____
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solvent
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Substances dissolved in water are _____
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solutes
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Osmosis
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- the diffusion of water from an area of LOW solute concent. (lots of water) to an area of HIGH solute concent. (low amnt of water)
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Hypertonic solution "more than"
(HIGH solute, LOW water outside cell) |
- has a higher solute concent.
- water moves OUT of THE CELL b/c external sol'n is hyper - cell SHRIVELS - in plants, cell body shrinks from cell wall |
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Hypotonic solution "less than"
(LOW solute, HIGH water outside cell) |
- has a lower solute
- water moves INTO THE CELL b/c external sol'n is hypo - cell SWELLS & eventually bursts - in plants, known as turgid (makes cell rigid) cell |
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Isotonic solution "the same"
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-water diffuses in & out of cell at same rate
- cell size DOESNT change - in plants, known as flaccid cell |
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Aquaporins
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- how water flows through living cells
- are specialized channels - discovered by Peter Agre (studied movement of water) |
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THe force needed to stop osmotic flow is ____
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osmotic pressure
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Cells maintain osmotic balance by:
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1. extrusion- such as contractile vacuoles which removes water from cells continuosly
2. isosmotic regulation- keeping cells isotonic w/ their environment 3. Turgor- plant cells use turgor pressure to push cell membrane against the cell wall to keep it rigid |
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Active Transport
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-requires Energy usually in form of ATP
-moves substances UP their concent. gradient (from LOW to HIGH) - can be DIRECT or INDIRECT |
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Carrier proteins used in active transport are:
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1. uniporters- move 1 molecule @ a time
2. symporters- move 2 molecules in SAME direction 3. antiporters- move 2 molecules in OPPOSITE directions |
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Direct use of ATP: Sodium- Potassium pump
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-uses an antiporter to move 3 Na+ OUT OF THE CELL and 2 K+ INSIDE THE CELL
-phosphorylation and dephosphorylation changes the confirmation of the carrier protein - affinity of the carrier protein for either ion changes so they get across membrane - see figure 5.15 (p.98) for drawing |
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Indirect use of ATP: Coupled Transport
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- uses the E released when a molecule moves by diffusion to supply E to active transport of a differ molecule
- uses a symporter - glucose-Na+ symporter captures E from Na+ diffusion to move glucose against a concent. gradient |
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Countertransport
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- similar to coupled transport
- directions of the molecules are opposite - uses an antiporter |
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Endocytosis
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- how materials enter the cell
- 3 major types: 1.phagocytosis 2.pinocytosis 3.receptor-mediated endocytosis -these processes require energy! |
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Phagocytosis
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- when material being taken in is particulate (made of discrete particles)
- "to eat" the "cell" |
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Pinocytosis
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- when material being taken in is a liquid
- "to drink" - common among animal cells |
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Receptor-mediated endocytosis
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- way in which molecules are often transported into eukaryotic cells
- involves the use of the protein known as clathrin - LDL is taken up by this process |
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Exocytosis
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- way in which materials leave the cell
- discharged from vesicles - in plants, means of exporting materials needed to construct cell wall - in animal cells, secretes hormones, digestive enzymes - in protist, contractile vacuoles in an example |
