Chapter 7 - Membrane Structure and Function Flashcards
list the components of membranes
lipids, carbohydrates, proteins
list the functions of membranes
selective permeability barrier, compartmentalization of function, energy transduction, transport (water and solutes), site of some enzymatic activity, communication, intercellular joining, anchorage
describe the fluid mosaic model of membranes
membrane components and functions are asymmetric
define membrane fluidity
movement of membrane components (phospholipids and proteins)
list the 4 types of movement of phospholipids
lateral movement, rotation, flexing of fatty acids, flip-flop transverse diffusion
what is the importance of membrane fluidity?
important for basic cell processes to occur
what happens when membranes are too fluid?
loss of structural organization and mechanical support - membranes leak
what happens when membranes are too rigid?
mobility is poor - membranes leak
list the factors that affect membrane fluidity
temperature, lipid composition
define selective permeability
allow some things to cross but not others - eg phospholipid bilayers allow water to cross but not all solutes
how do hydrophobic molecules pass through the phospholipid bilayer?
simple diffusion
how do small, uncharged, polar molecules pass through the phospholipid bilayer?
transport proteins help them cross
how do large, uncharged, polar molecules pass through the phospholipid bilayer?
transport proteins are required to help them cross
how do inorganic and organic ions pass through the phospholipid bilayer?
transport proteins are required to help them cross
passive transport definition
diffusion of a substance across a membrane with no energy investment
define diffusion
spontaneous movement of particles of any kind from where they are more concentrated to where they are less concentrated
define concentration gradient
increase or decrease in the density of a chemical substance in an area
define osmosis
simple diffusion of free water across a selectively permeable membrane; moves from areas of low concentration of solute to high concentration to even out the concentration across the membrane
define an osmole
amount of substance that results in Avogadro’s number of particles when placed in solution
define osmotic pressure
a measure of the tendency of a solution to take up water when separated from pure water by a selectively permeable membrane; the amount of pressure that will just stop the flow of water
define tonicity
the ability of a solution to cause a cell within it to gain or lose water
what does it mean to be isosmotic with a medium fluid?
the same osmotic pressure as the medium
what does it mean to be hyperosmotic with a medium fluid?
osmotic concentration is higher than the medium
what does it mean to be hyposmotic with a medium fluid?
osmotic concentration is lower than the medium
what does it mean to be isotonic with a solution?
have the same solute concentration
what does it mean to be hypertonic with a solution?
the one with a greater solute concentration
what does it mean to be hypotonic with a solution?
the one with a lower solute concentration
define facilitated diffusion
passive transport mediated by channel proteins or carrier proteins
explain how channel proteins work
possess a hydrophilic channel through which atomic ions and some small molecules can pass; some are open all the time, others are gated
explain how carrier proteins work
undergo a shape change which takes small ions or molecules across
define active transport
movement of a substance across a membrane, through a transport protein, against a chemical or electrochemical gradient; requires energy input and is powered by ATP (or cotransport with a substance moving down its gradient)
define exocytosis
vesicular removal of molecules to the extracellular fluid
define constitutive exocytosis
ubiquitous and continuous, supplies proteins and lipids to the plasma membrane, secretes many molecules from the cell
define regulated exocytosis
operates in cells specialized for secretion, membrane fusion occurs only in response to extracellular signal
define membrane fusion
when membranes fuse with each other, the orientation of the leaflets remains the same
define endocytosis
vesicular uptake of molecules from the extracellular fluid
define phagocytosis
uptake of large, bulky material
define pinocytosis
non-specific uptake of fluid from extracellular fluid; occurs almost continuously in most cells
define receptor-mediated endocytosis
uptake of specific molecules from extracellular fluid
what builds the membrane?
the endoplasmic reticulum and Golgi apparatus