CH:4 - Cell Membranes and Transport Flashcards
(19 cards)
Fluid-Mosaic Model
The currently accepted model of membrane structure, proposed by Singer and Nicolson in 1972, in which protein molecules are free to move about in a fluid bilayer of phospholipid molecules.
Cholesterol
A small, lipid-related molecule with a hydrophilic head and a hydrophobic tail which is an essential constituent of membranes; it is particularly common in animal cells and gives flexibility and stability to the membrane as well as reducing fluidity.
Cell-signalling
The molecular mechanisms by which cells detect and respond to external stimuli, including communication between cells.
Ligand
A biological molecule which binds specifically to another molecule, such as a cell surface membrane receptor, during cell signalling.
Transduction
Occurs during cell signalling and is the process of converting a signal from one method of transmission to another.
Diffusion
The net movement of molecules or ions from a region of higher concentration to a region of lower concentration down a concentration gradient, as a result of the random movements of
particles.
Facillitated Diffusion
The diffusion of a substance through a transport protein (channel protein or carrier protein) in a cell membrane; the protein provides hydrophilic areas that allow the molecule or ion to pass through the membrane, which would otherwise be less permeable to it.
Channel Protein
A membrane protein of fixed shape which has a water-filled pore through which selected hydrophilic ions or molecules can pass by facilitating diffusion or active transport.
Carrier Protein
A membrane protein which changes shape to allow the passage into or out of the cell of specific ions or molecules by facilitated diffusion or active transport.
Osmosis
The net diffusion of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane.
Water Potential
A measure of the tendency of water to move from one place to another; water moves from a solution with higher water potential to one with lower water potential; water potential is decreased by the addition of solute, and increased by the application of pressure; the symbol for water potential is ψ or ψw.
Protoplast
The living contents of a plant cell, including the cell surface membrane but excluding the cell wall.
Plasmolysis
The loss of water from a plant or prokaryote cell to the point where the protoplast shrinks away from the cell wall.
Incipient Plasmolysis
The point at which plasmolysis is about to occur when a plant cell or a prokaryote cell is losing water; at this point the protoplast is exerting no pressure on the cell wall.
Active Transport
The movement of molecules or ions through transport proteins across a cell membrane, against their concentration gradient, using energy from ATP.
Sodium–Potassium Pump (Na+ – K+ pump):
A membrane protein (or proteins) that moves sodium ions out of a cell and potassium ions into it, using ATP.
Endocytosis
The bulk movement of liquids (pinocytosis) or solids (phagocytosis) into a cell, by the infolding of the cell surface membrane to form vesicles containing the substance; endocytosis is an active process requiring ATP.
Exocytosis
The bulk movement of liquids or solids out of a cell, by the fusion of vesicles containing the substance with the cell surface membrane; exocytosis is an active process requiring ATP.
Phagocyte
A type of cell that ingests (eats) and destroys pathogens or damaged body cells by the process of phagocytosis; some phagocytes are white blood cells.
