cell membranes Flashcards
list three functions of cell membranes
- cell recognition
- control of transport of substances
- contains organelles
what is the name of the arrangement of cell membrane?
fluid-mosaic model
why is it described as a fluid-mosaic model?
fluid- individual phospholipid molecules can move relative to one another so membrane is flexible and can change shape
mosaic - scattered proteins embedded in bilayer varies pattern, shape and size like a mosaic
name five molecules in a cell membrane
- phospholipid
- cholesterol
- glycolipid
- protein
- glycoprotein
- cholesterol
what type of layer do the phospholipids form?
bilayer
describe structure of bilayer
- hydrophilic head point out - attracted to water
- hydrophobic head points in - repelled by water
what are the functions of the phospholipids?
- make membrane flexible
- allow entry/exit of lipid-soluble substances
- prevent entry/exit of water-soluble substances
what are the two types of protein in membrane?
- intrinsic
- extrinsic
name two types of intrinsic proteins
- channel proteins
- carrier proteins
how does a channel protein work?
facilitated diffusion - forms a water-filled hydrophilic channel across membrane
- charged particles diffuse down gradient
how do carrier proteins work?
facilitated diffusion - large molecules attached to membrane and protein changes shape so then it releases the molecule on opposite side of membrane
functions of proteins in membrane
- structural support
- act as channels
- allow active transport/ facilitated diffusion through carrier proteins
- helps cells adhere together
- act as receptors
where are glycoproteins attach on membrane?
carbohydrate chain attached to extrinsic proteins
functions of glycoprotein
- cell recognition
- cell receptors - hormones/ neurotransmitters
- help cells attach and form tissues
what is a glycolipid made of?
a carbohydrate covalently bonded to a lipid
where are glycolipids in membrane?
extends from bilayer into water environment
functions of glycolipid
- cell receptor (ABO blood)
- cell recognition
- stability of membrane
- help cells attach and form tissues
how does cholesterol affect the movement of molecules in cell membrane?
restricts movement because it pulls together fatty acid tails
other functions of cholesterol
- reduces lateral movement of phospholipids
- prevents leakage of water and dissolved ions from cell because it is hydrophobic
- makes membrane less fluid at high temperatures
name three factors that affect the permeability of membranes
- pH
- solvent
- temperature
how does pH affect the permeability of membranes?
- low pH - proteins are denatured due to interference of hydrogen bonding
- holes are formed so molecules pass through by diffusion and disrupts mosaic pattern
how do solvents affect the permeability of membranes?
higher concentration of solvent the more permeable
- ethanol dissolves phospholipids due to polar/non-polar ends
- it affects fluidity of membrane by denaturing function of embedded proteins
- mosaic falls apart so molecules easily diffuse through
how does temperature affect the permeability of membranes?
- at high temp, molecules vibrate faster and water expands putting pressure on membrane
- lipids more fluid so membranes are fragile
- proteins denature because vibrations disrupt hydrogen bonding
- membrane will have gaps for molecules to diffuse through
