Term
| Functions of plasma membranes |
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Definition
- physical boundaries
- enable cell-cell recognition
- compartmentalize eukaryotic cells
- attach to cytoskeleton and extracellular matrix
- sites for receptor molecules (GPCR), transporters (Na), pumps (proton pumps)
- sites for biological reactions (electron transport chain in mitochondria) |
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Term
| Composition of plasma membrane |
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Definition
5nm thick tri-partite structure
- 2 hydrophilic sandwiches hydrophobic core
- Intermembrane proteins throughout |
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Term
| Characteristics of phospholipid and membrane |
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Definition
Hydrophobic tails: each contains 14-24 Carbon atoms
- Shorter tails = more fluid membrane
- Longer tails (un-bent) = more stable membrane
- Cholesterol makes membrane less fluid.
Phosphatidylcholine is most common phospholipid, has choline attached to phosphate. |
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Term
| Process of freeze fracture to view membrane through TEM |
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Definition
E-face = cell exterior
P-face = protoplasm (cell interior)
1) rapidly freeze cells in liquid freon
2) frozen cells fractured with cold knife
3) Bilayer fractures through hydrophobic core
4) Fractured surface coated with heavy metal
5) Fractured cell dissolved with acid, metal replica remains
6) TEM examines metal replica of cell
To determine if cell is damaged: separate membrane layers, put at room temp and see if cells are still viable.
- Rapid freezing doesn't destroy cells |
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Term
| Arrangement of membrane proteins |
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Definition
Integral membrane proteins attach cells to each other and to extracellular matrix, and form channels, receptors, transporters. Need to disrupt membrane with detergent to extract them.
Peripheral membrane proteins: attached by weak bonds, regulate transporters and receptors. |
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Term
| Alpha helix/beta sheet traversing membrane |
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Definition
Alpha helix: hydrophobic side chains contact membrane, hydrophilic parts form water-filled pore
Beta sheet: |
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Term
| Functions of plasma membrane proteins |
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Definition
- Transporter: Bacteriorhodopsin is transporter that pumps protons
- Anchor: Cadherin family molecules of desmosomes anchor cells together
- Receptor: Platelet-derived growth factor (PDGF) is receptor for extracellular PDGF and generates intracellular signals
- Enzymes: Adenylyl cyclase enzymatically produces cyclic AMP in cell in response to extracellular signals. |
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Term
| Describe experiment demonstrating fluidity of plasma membrane proteins |
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Definition
| Mouse protein isolated, red antibodies (fluorescent dye) injected. Human protein isolated, green antibodies injected. -> Cell fusion -> antibodies had mixed. |
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Term
| Why is lateral movement in natural cells not as fast as artificial cells? |
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Definition
Because of contact with:
1) cytoskeleton
2) extracellular matrix
3) proteins of adjacent membranes
4) Tight junctions also prevent lateral mobility. |
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Term
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Definition
| Glycolipids are only on extracellular surface |
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Term
| What is glycocalyx? What is it made of, what does it do? |
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Definition
Glycocalyx is a extracellular carbohydrate coating, consists of glycoproteins and glycolipids. (Proteoglycans are glycoproteins longer carbohydrate chains)
Protect surface and help in cell-cell recognization |
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Term
| Where is plasma membrane synthesized? |
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Definition
Membrane synthesis occurs in the endoplasmic reticulum.
FLIPPASE flips phospholipids to other side of membrane (from ER to extracellular side) |
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Term
| What is involved in active transport? |
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Definition
ATP used to pump molecules against concentration gradient. Uses transporters.
Transporters and channels mediate passive transport.
Membranes are impermeable to ions. |
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Term
| Transporter molecules in mitochondria |
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Definition
Transporters in mitochondria import pyruvate and export ATP.
ATP synthase in inner mitochondrial membrane uses proton flow to generate ATP. In lysosomes, ATP synthase functions opposite and uses ATP to pump protons into lysosome against concentration gradient. |
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Term
| What is one role of calcium transporter? |
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Definition
Returning calcium to Sarcoplasmic Reticulum after muscle contraction.
Binding of ATP causes conformational changes to Ca pump, Ca pumped from cytosol to SR |
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Term
| What does bacteriorhodopsin do? |
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Definition
Bacteriorhodopsin is a transporter that acts as proton pump.
- 7 alpha helices
Light energy changes shape of retinal -> retinal induces small change in bacteriorhodopsin to allow protons to pass through -> drives ATP synthesis
- Light drives ATP synthesis in these bacteria. |
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Term
| Different strategies for controlling water gain from osmosis |
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Definition
Animals: ions pumped out
Plants: cell wall prevents bursting, sugar converted to starch (no osmotic pressure)
Protozoa: water pumped out by contractile vacuole |
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Term
| How is H+ gradient used to drive solute uptake? |
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Definition
Proton transporter pumps out H+ ions, creating electrochemical proton gradient.
Proton gradient then drives H+ symports, protons reimported into cell with solutes. |
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Term
| Describe action of Na/K pump. |
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Definition
Na binds to pump, pump phosphorylates itself (gains phosphate by using ATP), conformational change in pump results and Na pumped out.
K binds to pump, pump dephosphorylates, K released into cell. |
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Term
| How do ions pass through ion channels? |
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Definition
- Width and charge of ion channels make them selective for certain ions.
In aqueous solution, each ion is surrounded by shell of water that prevents passage.
Water molecules are transiently removed to allow passage. |
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