C.7 Membranes Flashcards
Amphipathic phospholipids in membrane structure
Contains hydrophobic (core) and hydrophilic regions (outside, exposed to water). Phospholipids are the most abundant lipid in the plasma membrane, but proteins follow the amphipathic structure.
membrane fluidity
Phospholipids can move within bilayer, most drift laterally but may ‘flip-flop’ transversely across the membrane.
Usually about as fluid as salad oil; as temperature cools, membranes switch from a fluid state to a solid (gel) state
fatty acids and cholesterol on membrane fluidity
Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acid.
Cholesterol at warm temperatures restrains movement of phospholipids, preventing the membrane from becoming too fluid. At cool temperatures, it maintains fluidity by preventing tight packing.
two types of membrane proteins
Integral proteins: Penetrate the hydrophobic core and requires at least one stretch of hydrophobic Amino acids
Peripheral proteins: bound to the surface of the membrane on one side. Less hydrophobic Amino acids
Describe the functions of membrane proteins
- Transport: moves materials in and out of cell
- Enzymatic activity: ex. ATP Synthase
- Signal transduction: communicates outside messages to cell inside
- Cell-cell recognition: helps indentify correct cells to interact with
- Intercellular joining: stick cells together to form tissues
- Attachment to the cytoskeleton and ECM: attachs cell to surround and interacts with interior protein
Effect of Selective permeability
Hydrophobic/non-polar: lipid soluble, rapidly dissolves to pass through membrane (eg. gas, fatty acid, steroid)
Hydrophilic/polar: not lipid soluble, cannot easily pass through membrane (eg. sugars, amino acids, ions)
transport proteins (channels, carriers and pumps)
Channels: facilitated diffusion
Carrier: moves a single substance ??
Pumps: requires atp ??
passive transport
Diffuses down the concentration gradient, from higher to lower solute. Requires no energy; spontaneous. Includes osmosis.
tonicity
Solute concentration inside a cell vs the outside solution. Can cause a cell to lose or gain water.
active transport
uses proteins embedded in the membrane to transport against the concentration gradient, requires energy
active transport
uses proteins embedded in the membrane to transport against the concentration gradient, requires energy
Isotonic
concentration is the same in and out of the cell, resulting in no net movement of water across the plasma membrane. Normal for animal cells. Plant cells will wilt, requires more water inside the cell.
Hypertonic
Concentration is greater out of the cell; the cell will lose water. Animal cell will crenate. Plant cell will plasmolyse, as the membrane will pull away from the cell wall.
Hypotonic
Concentration is greater out of the cell; the cell will gain water. Animal cell will swell and burst, lysis. Normal for plant cell; it is turgid, pressing against the wall.
Exocytosis
Cell expels macromolecule. Transport vesicle contains it, goes to plasma membrane and fuses with it, then releases it outside cell. eg. secretory cells
