1.3 Membrane Structure Flashcards
Why is fluidity controlled ?
level of fluidity is controlled to ensure that the membrane does not solidify or too fluid because membrane controls what goes in and out of the cell
so any change in the membrane would affect the exchange of materials of the cell
define amphipathic define polar (hydrophilic) define non-polar (hydrophobic)
having both a hydrophilic and hydrophobic part
hydrophilic - attracted to water
hydrophobic - repelled by water
what happens to phospholipid in water
they form into a bilayer due to their amphipathic property. They have a polar (hydrophilic) head and non-polar (hydrophobic) fatty acid tails.
Their emergent property is that they keep their heads “wet” and their tails “dry”
how do lipid bilayer component move ?
they can flow past each other laterally but not vertically
what are the the main types of membrane proteins
integral proteins (intrinsic) - there are polytopic and monotopic proteins. They are both permanently embedded to the membrane. The polytopic spans throughout multiple surfaces whereas the monotopic is only attached to one side of the phospholipid
peripheral proteins (extrinsic) - temporary associated with the membrane
What are glycoproteins and explain the uses of it
glycoproteins - proteins with oligosaccharide chain attached
important for cell recognition by immune system and as hormone receptors
Function of membrane proteins ?
mnemonic - JETRAT
J unctions - serve to connect and join two cells tgt
E nzymes - catalyse reactions
T ransport - Responsible for facilitated diffusion and active transport
R ecognition - May function as markers for cellular identification
A nchorage - Attachment points for cytoskeleton and extracellular matrix
T ransducton - Function as receptors for peptide hormones
function of cholesterol
makes the phospholipids pack more tightly and regulates the fluidity and flexibility of the membrane.
what is cholesterol a component of ? explain the components of cholesterol
cholesterol is amphipathic like a phospholipid they are components of an animal membrane
Hydroxyl group makes the head polar (hydrophilic) - attracted to the phosphate heads of the phospholipids
steroid carbon rings and non-polar (hydrophobic) tail –attracted to the phospholipid tails
why is cholesterol absent in plant cells ?
these plasma membranes are surrounded and supported by a rigid cell wall made of cellulose
how does cholesterol reduce membrane fluidity and permeability to some solutes ?
- restrict movement of phospholipid and molecules - reducing membrane fluidity
- at low temps - disrupts regular packing of hydrocarbon tails to prevent solidification of membranes - stay more fluid
- reduces permeability to hydrophilic molecules and ions such as sodium and hydrogen
What was the old belief about the structure of membranes and what is the one called now ?
davson Danielle model and now it is called the fluid mosaic diagram or the singer Nicholson model
compare and contrast the Davson Danielli and fluid mosaic diagram of cell membranes
Differences
Davson Danielli model
- lipid bilayer sandwiched between two protein layers
Fluid mosaic diagram
- Phospholipid molecules form a bilayer - phospholipids are fluid and move laterally
- the phospholipid bilayer is embedded with proteins
- Proteins can move laterally along membrane
Similarities
- they are both phospholipid bilayer
- both recognizes proteins involved in the structure
The falsification of the Davson Danielli model
- Membrane proteins were discovered to be insoluble in water (indicating hydrophobic surfaces) and varied in size
- Fluorescent antibody tagging of membrane proteins showed they were mobile and not fixed in place
- Freeze fracturing was used to split open the membrane and revealed irregular rough surfaces within the membrane
