membranes Flashcards
(24 cards)
describe structure of cell membrane
- phospholipid bilayer
- extrinsic proteins
- intrinsic (channel) proteins
- glycolipids
- glycoproteins
- cholesterol
what is the role of cholesterol in cell membrane?
connects phospholipids and reduces fluidity to make bilayer mroe stable
what is the role of glycolipids in the cell membrane?
cell recognition and cell signalling
what is the role of extrinsic proteins in the cell membrane?
- binding sites/receptors
- antigens (glycoproteins)
- cell signalling
what is the role of intrinsic proteins in the cell membrane?
- channel proteins
- allows large polar molecules through
what is the function of a membrane in a cell?
- internal transport system
- reaction surface
- selectively permeable to regulate passage of molecules
factors that affect membrane permeability
- temperature - high temp denatures membrane proteins, phospholipid molecules have more KE so move apart
- pH changes tertiary structure of membrane proteins
- solvent may dissolve membrane
osmosis definition
net movement of water through a partially permeable membrane from a high water potential to a low water potential
water potential definition
measure of the quantity of water compared to solute measured as pressure created by water molecules in kilopascals (kPa)
turgid definition
when a plant cell is full of water and membrane pushes against cell wall
plasmolysis definition
plant cell membrane pulls away from cell wall as water leaves
haemolysed definition
animal cell bursts open when excess water enters
crenated definition
animal cell shrinks and is wrinkled due to loss of water
flaccid definition
plant cell lost some water so cell contents do not push against cell wall
what is the role of cell signalling?
allows multicellular organisms to communicate across the body
examples of cell signalling
- neurotransmission
- cell adhesion
- hormones
- cell recognition
how does cell signalling work?
- glycolipids and glycoproteins act as receptors on surface of cell
- ligand is released by exocytosis
- receptor and ligand (signal) are complementary
- attachment of the ligand to recepetor triggers change in cell
simple diffusion definition
passive process so requires no energy
net movement of small, lipid soluble molecules directly through bilayer from area of high concentration to area of low concentration
facilitated diffusion definition
passive process
specific channel or carrier proteins with complementary binding sites transport large polar molecules down concentration gradient
how do channel and carrier proteins work?
channel - hydrophilic channels bind to specific ions - one side of protein closes and other opens
carrier - change releases molecule on other side of membrane - requires energy in active transport - passive process in facilitated diffusion
active transport definition
ATP hydrolysis releases phosphate group that binds to carrier protein causing change in shape - specific carrier protein transports molecules against concentration gradient
exocytosis and endocytosis defintions
active process
involved in bulk transport and transporting large particles
vesicles fuse with cell surface phospholipid membrane
factors that affect the rate of diffusion
- temperature
- diffusion distance
- surface area
- size of molecule
- how steep the concentration gradient is
