b2.2 membrane transport Flashcards
(37 cards)
what is the function of a cell membrane?
cell membranes function to enclose the contents of the cell, separating the intracellular components from the external environment. this allows for the control of internal conditions within the cell and the maintenance of homeostasis.
what qualities do cell membranes possess?
cell membranes possess two key qualities that function to provide homeostatic regulation: semi-permeability where only certain materials are able to freely cross the cell membrane and selectivity where the cell can control the passage of any material that cannot freely cross the membrane.
what is the phospholipid bilayer?
the phospholipids form a bilayer that acts as a barrier to certain materials. the hydrocarbon chains that form the core of the bilayer are hydrophobic and have low permeability to large and charged substances. this means that large compounds and hydrophilic particles (ions and polar molecules) cannot cross the bilayer.
what are membrane proteins?
membrane proteins are embedded within the phospholipid bilayer may act as points of transport for large and charge substances. this makes the lipid bilayer a selective barrier as the membrane proteins can coordinate the transport of hydrophobic materials according to need.
what is diffusion?
diffusion is the net movement of molecules from a region of high concentration to a region of low concentration. this directional movement along a gradient is passive and will continue until molecules become evenly dispersed (equilibrium).
what factors affect the rate of diffusion?
temperature, molecular size, steepness of gradient
what are integral proteins?
integral proteins penetrate the phospholipid bilayer to remain permanently attached to the membrane. these transmembrane proteins cannot be readily isolated without disrupting the bilayer. examples of integral membrane proteins include glycoproteins, ion channels, carrier proteins and protein pumps.
what are peripheral proteins?
peripheral proteins are only temporarily associated with one side of a membrane. they are either attached to integral proteins, linked to the polar heads of the bilayer. examples of peripheral proteins are receptor complexes involved in cell signaling.
what is the composition of a membrane protein?
the composition of a membrane protein is determined by its function within the cell. non-polar amino acids will associate with the lipid bilayer, while polar amino acids will face the aqueous solutions. the inner surface of a protein channel will be lined with polar amino acids to facilitate the passage of specific polar or charged molecules
what are the functions of membrane proteins?
junctions, enzymes, transport, recognition, anchorage, transduction
what is osmosis?
osmosis is the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration. while water is moving to a more to a more concentrated solution, osmosis is still a passive process as there are less free water molecules when solute levels are higher.
what are aquaporins?
cell membranes also possess integral proteins called aquaporins that function as water channels within the bilayer. aquaporins facilitate a much faster ate of water transport in response to solute concentrations and their levels can be regulated to help control the osmotic conditions of a cell.
what is facilitated diffusion?
facilitated diffusion is the passive movement of molecules across the cell membrane via the aid of a membrane protein. it is utilised by molecules that are unable to freely cross the phospholipid bilayer. this process is mediated by two distinct types of transport proteins - channel proteins and carrier proteins.
what is active transport?
active transport uses energy to move molecules against a concentration gradient. this energy may be generated either by the direct hydrolysis of ATP or indirectly coupling transport with another molecule that is moving along its gradient.
how does active transport use membrane proteins?
active transport involves the use of membrane proteins (protein pumps). a specific solute will bind to the protein pump on one side of the membrane. the hydrolysis of ATP causes a conformational change in the protein pump. the solute molecule is consequently translocated across the membrane and released.
what is the difference between passive transport and active transport?
passive transport involves the movement of material along a concentration gradient. because materials are moving down a concentration gradient, it does not require the expenditure of energy.
active transport involves the movement of materials against a concentration gradient. because materials are moving against the gradient, it does require the expenditure of energy.
what is glycosylation?
phospholipids and membrane proteins can have carbohydrate chains attached via the process of glycosylation. the carbohydrate chains are located on the extracellular side of the membrane and play important roles in cell adhesion and cell recognition (attachment point for other cells or a point of recognition between cells).
how do glycoproteins and glycolipids have a structural function?
glycoproteins and glycolipids also play an important role in maintaining the structural integrity of the extracellular matrix. the extracellular matrix is a network for external molecules that provide structure and biochemical support to surrounding cells. the carbohydrate chains can link these extracellular molecules together to help make the matrix a cohesive network.
what is the fluid mosaic model?
cell membranes are represented according to a fluid-mosaic model, due to the fact that they are: fluid as the phospholipid bilayer is viscous and individual phospholipids can move position, and mosaic as the phospholipid bilayer is embedded with proteins, resulting in a mosaic of components.
what is the effect of unsaturated fatty acids in the membrane?
unsaturated fatty acids have double bonds in their lipid chain which results in a kinked hydrocarbon tail. this means that the lipids are harder to pack together, lowering their viscosity and increasing fluidity. unsaturated fatty acids in lipid bilayers also have lower melting points, so membranes are more fluid and flexible at temperatures experienced by a cell.
what is the effect of saturated fatty acids in the membrane?
saturated fatty acids have no double bonds in their lipid chain which results in a straight hydrocarbon tail. this means the lipids will be easier to pack together, increasing their viscosity and lowering fluidity. saturated fatty acids have higher melting points and make membranes stronger and more stable at higher temperatures.
how do organisms regulate membrane fluidity?
many organisms will adjust the composition of lipids in their membranes in order to regulate membrane fluidity. the general trend is an increase in unsaturated fatty acids at lower temperatures and an increase in saturated fatty acids at higher temperatures. regulating membrane fluidity is particularly important in organisms whose internal body temperatures vary considerably.
how does cholesterol maintain membrane fluidity?
cholesterol is a ringed lipid and an amphipathic molecule that acts as an adjustor of membrane fluidity. at high temperatures, it functions to stabilise the membrane and raises the melting point, lowering fluidity. at lower temperatures, it intercalates between the phospholipids, preventing stiffening and crystallisation, raising fluidity.
what functional roles does cholesterol have in the membrane?
cholesterol also fulfils certain functional roles within a plasma membrane. it makes the membrane less permeable to very small water-soluble molecules that would otherwise freely cross. it helps secure peripheral proteins by forming high density lipid rafts capable of anchoring the protein.
