Chapter 8 - Membrane Structure and Function
Terms
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- Selective permeability
-
a key feature of plasma membranes;
allows some substances to cross a membrane more easily than others - Amphipathic
- contains both water-loving and water-fearing components
- Fluid mosaic model
-
the current model used to describe the structure of membranes;
according to this model, the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids - Integral proteins
- generally transmembrane proteins, with hydrophobic regions (stretches of nonpolar amino acids) that completely span the hydrophobic interior of the membrane
- Peripheral proteins
-
proteins that are not embedded in the lipid bilayer at all;
loosely bound to the surface of the membrane, often to the exposed parts of integral proteins - Transport proteins
- integral proteins that selectively transport molecules across the membrane
- Diffusion
-
the tendency for molecules of any substance to spread out into the available space;
a spontaneous process that decreases free energy - Concentration gradient
- in the absence of other forces, a substance will diffus efrom where it is more concentrated to where it is less concentrated (down its conc. gradient)
- Passive transport
-
the diffusion of a substance across a biological membrane;
the cell does not have to expend energy to make this happen - Hypertonic
- when comparing two solutions of unequal solute concentration, refers to the solution with a higher conc. of solute
- Hypotonic
- when comparing two solutions of unequal solute concentration, refers to the solution with a lower conc. of solute
- Isotonic
- describes two solutions that are equal in solute conc.
- Osmosis
-
a spcial case of active transport;
diffusion of water across a selectively permeable membrane - Osmoregulation
- the control of water balance
- Facilitated diffusion
- the spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their conc. gradients
- Gated channels
-
proteins that respond to a stimulus by opening or closing;
stimulus may be electrical or chemical - Active tranpsort
- a process by which a cell moves a solute against its conc. gradient by expending its own energy
- Sodium-potassium pump
-
a transport protein which exchanges sodium for potassium across the membrane of animal cells in order to maintain specific conc. of each within the cell;
the main electrogenic pump of animal cells - Membrane potential
-
the voltage across a membrane;
reflects the separation of charges across a membrane - Electrochemical gradient
- the combination of the electrical gradient and the chemical gradient that drive the movement of ions across membranes
- Electrogenic pump
- a transport protein that generates voltage across a membrane, storing energy in the form of voltage
- Proton pump
-
the main electrogenic pump plant, fungi, and bacteria cells;
actively transports hydrogen ions out of the cell - Cotransport
- a mechanism by which a single ATP-powered pump that transports a specific solute can indirectly drive the active transport of several other solutes
- Exocytosis
- a process by which cells secrete macromolecules by the fusion of vesicles with the plasma membrane
- Endocytosis
- a process by which cells take in macromolecules and particular matter by forming new vesicles from the plasma membrane
- Phagocytosis
- a process by which a cell engulfs a particle by wrapping pseudopodia around it and packaging it within a membrane enclosed sac; the sac then combines with a lysosome and the particle is digested
- Pinocytosis
- a process by which the cell "gulps" droplets of extracellular fluid in tiny vesicles
- Receptor-mediated endocytosis
- endocytosis that occurs when a specific molecule comes into to contact with specific membrane proteins
- Ligands
-
a general term for any molecule that binds specifically to a receptor site of another molecule;
from the Latin "ligare" which means "to bind"