Chapter 5 Biological Membranes Flashcards
plasma membrane
The selectively permeable surface membrane
that encloses the cell contents and through which all materials entering or leaving the cell must pass.
fluid mosaic model
The currently accepted model of the plasma
membrane and other cell membranes, in which protein molcules “float” in a fluid phospholipid bilayer.
amphipathic
A molecule containing both hydrophobic and hydrophilic regions.
Integral membrane proteins
A protein that is tightly associated with
the lipid bilayer of a biological membrane; a transmembrane integral protein spans the bilayer. Compare with peripheral membrane protein.
Transmembrane proteins
An integral membrane protein that spans the lipid bilayer.
Peripheral membrane proteins
A protein associated with one of the surfaces of a biological membrane. Compare with integral membrane protein.
selectively permeable membranes
A membrane that allows some substances to cross it more easily than others. Biological membranes are generally permeable to water but restrict the passage of many solutes.
transport proteins
facilitate the passage of certain ions and molecules through biological membranes.
Carrier proteins
transport proteins that undergo a series of conformational changes as they bind and transport a specific solute
ABC transporters
ATP-binding cassette transporters
Channel proteins
transport proteins that form passageways through which water and certain ions travel through the membrane.
Porins
transport proteins that form passageways through which water and certain ions travel through the membrane.
Diffusion
The net movement of particles (atoms, molecules, or ions)
from a region of higher concentration to a region of lower concentration (i.e., down a concentration gradient), resulting from random motion
concentration
gradient
A difference in the concentration of a substance from one point to another, as for example, across a cell membrane.
simple diffusion
solute molecules or ions move directly through the membrane down their concentration gradient.
Facilitated diffusion
The passive transport of ions or molecules by a specific carrier protein in a membrane. As in simple diffusion, net transport is down a concentration gradient, and no additional energy has to be supplied
Osmosis
The net movement of water (the principal solvent in biological systems) by diffusion through a selectively
permeable membrane from a region of higher concentration of water (a hypotonic solution) to a region of lower concentration of water (a hypertonic solution).
osmotic pressure
The pressure that must be exerted on the hypertonic
side of a selectively permeable membrane to prevent
diffusion of water (by osmosis) from the side containing pure water.
isotonic
A term applied to solutions that have identical concentrations of solute molecules and hence the same
osmotic pressure. Compare with hypertonic and hypotonic.
hypertonic
osmotic pressure (or solute concentration) greater than that of the solution with which it is compared.
plasmolysis
The shrinkage of cytoplasm and the pulling away of the plasma membrane from the cell wall when a plant cell (or other walled cell) loses water, usually in a hypertonic
environment.
hypotonic
osmotic pressure (or solute concentration) less than that of the solution with which it is compared.
cotransport
The active transport of a substance from a region of low
concentration to a region of high concentration by coupling its transport to the transport of a substance down its concentration gradient.
exocytosis
The active transport of materials out of the cell by fusion of cytoplasmic vesicles with the plasma membrane.
endocytosis
The active transport of substances
into the cell by the formation of invaginated regions of the plasma membrane that pinch off and become cytoplasmic vesicles.
phagocytosis
Literally, “cell eating”; a type of
endocytosis by which certain cells engulf food particles, microorganisms, foreign matt er, or other cells.
pinocytosis,
Cell drinking; a type of endocytosis by which cells engulf and absorb droplets of liquids.
receptor-mediated endocytosis
A type of endocytosis in which extracellular molecules become bound to specific receptors on the cell surface and then enter the cytoplasm enclosed in vesicles.
ligand molecules
A molecule that binds to a specifi c site in a receptor or other protein.
Anchoring junctions
include desmosomes and adhering junctions; they are found between cells that form a sheet of tissue.
Desmosomes
Buttonlike plaques, present on two opposing cell surfaces, that hold the cells together by means of protein filaments that span the intercellular space.
Adhering
junctions
A type of anchoring junction between cells; connects
epithelial cells.
Tight junctions
Specialized structures that form between some animal cells, producing a tight seal that prevents materials from passing through the spaces between the cells.
Gap junctions
Structure consisting of specialized regions of the plasma membrane of two adjacent cells; contains numerous pores that allow the passage of certain small molecules and ions between them.
Plasmodesmata
Cytoplasmic channels connecting adjacent plant cells and allowing for the movement of molecules and ions between cells.
turgor pressure
Hydrostatic pressure that develops within a walled cell and presses outward against the plasma membrane.
active transport
Transport of a substance across a membrane that does not rely on the potential energy of a concentration gradient for the substance being transported and therefore requires an additional energy source (oft en ATP); includes carrier-mediated active transport, endocytosis, and exocytosis
sodium–potassium pump
Active transport system that transports sodium ions out of, and potassium ions into, cells.
