cell membranes and transport Flashcards
components of cell membranes
- phospholipids
- protein (extrinsic, intrinsic)
- glycoproteins
- glycolipids
- cholestorol
structure of phospholipid bilayer
- inner layer = hydrophilic heads pointing towards the cell, touches cell cytoplasm
- outer layer = hydrophilic heads point outwards, touch water surrounding cell
- membrane centre = hydrophobic tails face each other
what does the phospholipid bilayer allow through
- lipid soluble molecules
- small un polar molecules
extrinsic proteins in phospholipid bilyer
- partially span membrane
- structural support
- form recognition sites to identify cells
- receptor sites of hormone attachment
intrinsic proteins in phospholipid bilayer
- span both layers
- carriers transport water soluble substances across
- allow AT of ions by forming channels
carrier or channel
function of glycoproteins and glycolipids in phospholipid bilayer
- hormone receptors
- cell-to-cell recognition
- cell adhesion
- in outer layer
function of cholesterol in phospholipid bilayer
- only in animal cells
- provide rigidity and stability
what is the glycocalyx on phospholipid bilayer
- extracellular surface of glycosylated proteins
- acts as a barrier
- provides protection
what is the fluid mosaic model
- fluid; individual phospholipids can move relative to each other
- mosaic; proteins embedded vary in shape, size, pattern
what is the phospholipid bilayer permeable to
- it is selectively permeable
- lipid soluble substances (Vit A) and dissolved molecules (O2, CO2) dissolve and move directly through
factors that increase the permeability of cell membranes
- temperature
- organic solvents
how does temp increase cell membrane permability
- above 40c
- increase vibrations of phospholipids
- they move further apart
how do organic solvents increase membrane permeability
- they dissolve phospholipids
what is the phospholipid bilayer not permeable to
- water soluble substances (ions, glucose, polar molecules) can’t pass through hydrophobic fatty acid tails
- must use intrinsic proteins
what is ficks law?
diffusion rate =
SA times difference in concentration
divided by
length of diffusion pathway
what is a channel protein?
- pores lined with polar (hydrophilic) groups
- allows charged ions through
- for diffusion and FD
what is a carrier protein?
- allows large, polar molecules through
e.g. water soluble, amino acids - molecule binds and the protein changes shape
- for FD, AT
- intrinsic
what is simple diffusion?
the movement of molecules from a region of high conc to low conc, down a conc gradient
- passive process (respiratory inhibitors have no effect)
- occurs through phospholipid bilayer
what is the diffusion rate increased by?
- higher conc gradient
- thinner membrane / shorter diffusion distance
- larger SA
- more pores in membrane
- smaller molecules
- being non-polar (fat-soluble)
- increased temperature
what is facilitated diffusion
process of diffusion for polar molecules that can’t directly pass through the phospholipid bilayer
- using protein channels / carriers
- eventually reaches a max rate due to limiting number of channels
- not affected by respiratory inhibitors
- passive
what is co-transport
- a type of FD where 2 different substances use the same carrier protein at the same time
stages of co-transport; when absorbing Na+ and glucose into blood and kidney nephron
- 1 glucose molecule, 2 Na+ bind to carrier protein, outside of cell
- protein changes shape. deposits them inside cell
- they diffuse separately through the cell
- reach other side. glucose enters blood by FD
- 2 Na+ carried out epithelial cell by AT. K+ ions move in on same carrier
- Na+ conc is always low in epithelial cell = brings more glucose in
(glucose moves against conc gradient)
what is active transport?
movement of molecules against conc gradient
requires energy from ATP from respiration
role of ATP in AT
ATP activates carrier proteins to move molecule across the cell membrane
- used to transport molecules across
