Term
| Five Inferences of the Early Plasma Membrane Model |
|
Definition
1. Membranes are made of lipids.
2. Amphipathic phospholipids can form membranes.
3. Cell membranes are bilayers.
4. Hydrophilic substances are found in cell membranes.
5. Membranes are coated with water-absorbant proteins. |
|
|
Term
| Inference: Membranes are made of lipids. |
|
Definition
| Evidence: Lipid and lipid-soluble materials enter cells more quickly than substances that are insoluble in lipids. |
|
|
Term
| Inference: Amphipathic phospholipids can form membranes. |
|
Definition
| Evidence: Amphipathic phospholipids will form an artificial membrane on the surface of water with only the hydrophilic heads immersed in water. |
|
|
Term
| Inference: Cell membranes are bilayers. |
|
Definition
| Evidence: Phospholipid content of membranes isolated from red blood cells is just enough o cover the cells with two layers. |
|
|
Term
| Inference: Hydrophilic substances are found in cell membranes. |
|
Definition
| Evidence: The surface of an actual biological membrane is more hydrophilic than the surface of an artificial membrane containing only of a phospholipid bilayer. |
|
|
Term
| Inference: Membranes are coated with water-absorbant proteins. |
|
Definition
| Evidence: Membranes isolated from red blood cells contain proteins as well as lipids. |
|
|
Term
|
Definition
| has both hydrophobic and hydrophilic regions. |
|
|
Term
| Sandwich Model proposed by |
|
Definition
| JF Danielli and H. Davson |
|
|
Term
|
Definition
| Phospholipid bilayer sandwiched between two layers of globular protein. The hydrophilic heads are oriented towards the protein layers, creating a hydrophilic zone and a hydrophobic zone. The membrane is ~8 nm thick. |
|
|
Term
| Electron microscopy provided evidence that supported the Davson-Danielli model: |
|
Definition
1. 7 to 8 nm thick
2. Trilaminar: two bands separated by an unstained layer. IT was assumed that stain adhered to the hydrophilic region but not to the hydrophobic region.
3. Internal cellular membranes looked similar to the plasma membrane. |
|
|
Term
| J.D. Robertson proposed that |
|
Definition
| all cellular membranes were symmetrical and identical. (WRONG) |
|
|
Term
| Problems with the Davson-Danielli Model |
|
Definition
1. Not all membranes are identical or symmetrical
- membranes with different functions have different structures
- membranes are bifacial
2. A membrane with an outer protein layer would be unstable.
- membrane proteins are also amphipathic. |
|
|
Term
|
Definition
| distinct inside and outside faces |
|
|
Term
| Fluid Mosaic Model proposed by |
|
Definition
| S.J. Singer and G.L. Nicholson |
|
|
Term
|
Definition
- Proteins imbedded in the bilayer
- Hydrophilic portions of proteins and phospholipids are maximally exposed to water
- Hydrophobic portions are in the non-aqueous environment inside the bilayer
- Membrane is a mosaic of proteins bobbing in a fluid bilayer of phospholipids
- confirmed by evidence from freeze fracture tests |
|
|
Term
|
Definition
| increase membrane fluidity |
|
|
Term
| Cholesterol's effect on eukaryotic membrane fluidity |
|
Definition
less fluid at warm temps. by restraining phospholipid movement
more fluid at low temps. by preventing close packing of phospholipids |
|
|
Term
|
Definition
| Generally transmembrane proteins with hydrophobic regions that completely span the hydrophobic interior of the membrane. |
|
|
Term
|
Definition
| Not embedded but attached to the membrane's surface. They may be attached to integral proteins or held by fibers of the ECM. On the cytoplasmic side, filaments of the cytoskeleton may hold them. |
|
|
Term
|
Definition
Two distinct faces; in membranes,
- two lipid layers may differ in lipid composition
- membrane proteins have distinct directional orientation
- carbs are restricted to exterior as glycoproteins or glycolipids that function in cell-cell recognition
- side of the membrane facing the lumens the same as the plasma membrane's outside face |
|
|
Term
|
Definition
| property of biological membranes which allows some substances to cross more easily than others |
|
|
Term
| Permeability of membrane depends on |
|
Definition
1. Particle characteristics (polarity and particle size)
2. Presence of transport proteins |
|
|
Term
|
Definition
- provide hydrophilic tunnel through membrane
- bind to a substance and move it
- are specific for substance
- can be saturated with solute
- can be inhibited by molecules resembling solute
- alternating conformations |
|
|
Term
|
Definition
| diffusion across a membrane |
|
|
Term
|
Definition
| A regular, graded concentration change over a distance in a particular direction. |
|
|
Term
|
Definition
| Spontaneous net movement of a substance down a concentration gradient. It results from kinetic energy and continues until a dynamo equilibrium is reached. It is not affected by the gradients of other substances. |
|
|
Term
|
Definition
| Passive transport of water or the diffusion of water across a selectively permeable membrane. |
|
|
Term
| Hypertonic or Hyperosmotic |
|
Definition
| Greater solute concentration compared to another |
|
|
Term
|
Definition
| Lower solute concentration compared to another |
|
|
Term
|
Definition
| Equal solute concentration compared to another |
|
|
Term
|
Definition
| Shrivel, can be caused in animal cells by a hypertonic environment |
|
|
Term
|
Definition
| Rupture due to excess water, can be caused in animal cells by a hypotonic environment |
|
|
Term
|
Definition
| removing water in a hypotonic environment or conserving water and pumping out salts in a hypertonic environment |
|
|
Term
|
Definition
| Firmness or tension, found in walled cells in a hypoosmotic environment. Ideal state of plant cells. |
|
|
Term
|
Definition
| Limpness of ell due to lack of net movement of water into or out of cell in an isotonic environment. |
|
|
Term
|
Definition
| Phenomenon where a walled cell shrivels an the plasma membrane pulls away from the cell wall as the cell loses water to a hypertonic environment. |
|
|
Term
|
Definition
| An energy-requiring process during which a transport protein pumps a molecule across a membrane against its concentration gradient. |
|
|
Term
|
Definition
A transport protein that, powered by ATP, oscillates between two confirmations to translocate 3Na+ out of the cell for every 2K+ into the cell:
- high affinity for Na+ with binding sites oriented towards the cytoplasm
- High affinity for K+ with binding sites oriented towards the exterior |
|
|
Term
|
Definition
| Voltage across membranes; the cell's inside is negatively charged with respect to the outside. |
|
|
Term
|
Definition
| diffusion gradient resulting from the combined effects of membrane potential and concentration gradient. |
|
|
Term
| Factors that contribute to a cell's membrane potential |
|
Definition
1. Negatively charged proteins within the cell
2. Plasma membrane's selective permeability to various ions (i.e. 3Na+ and 2K+)
3. The sodium-potassium pump |
|
|
Term
| Cell's Membrane Potential |
|
Definition
|
|
Term
|
Definition
| transport protein that generates voltage across the membrane that are sources of potential energy available for cellular work |
|
|
Term
|
Definition
Sodium-Potassium pump in animals;
Proton Pump in plants, bacteria, fungi, mitochondria, and chloroplasts |
|
|
Term
|
Definition
| A single ATP-powered pump actively transports one solute and indirectly drives the transport of other solutes against the concentration gradient; opposite: antiport |
|
|
