Plasma membranes Flashcards
What is the phospholipid bilayers structure?
-Hydrophilic phosphate head makes up both the inner and outer surface of a membrane, sandwiching the hydrophobic fatty acid tails.
Why does the phospholipid bilayer have its structure?
-Tends to be aqueous environments wither side of the membrane
Define hydrophobic
A non-polar substance which repels/is not attracted to water
Define hydrophilic
A polar substance which attracts water
Explain the fluid mosaic model
Refers to the phospholipids freeness to move within the layer, giving the membrane fluidity
What substances regulates membrane fluidity and how?
-Cholesterol, a lipid with a hydrophobic and a hydrophilic end.
-Positioned between phospholipids and pulls the heads and tails, keeping them at the correct distance from each other.
-Prevents membrane from becoming too solid by stopping phospholipid molecules from grouping too closely and crystallising
What is compartmentalisation?
The formation of separate membrane-bound areas in a cell.
Aids the specific conditions needed for cellular reactions, eg maintenance of chemical gradients
What is an extrinsic protein?
-Aka peripheral proteins, are present on one side of the membrane
-Normally have hydrophilic R-groups on their outer surfaces, interact with hydrophilic phosphate heads, keeps them in place.
-Can be present in either layer and some move between layers
-Eg glycoproteins
What is an instrinsic protein?
-Aka integral proteins, are transmembrane proteins that are embedded through both membrane layers.
-Have amino acids with hydrophobic R-groups on their external surfaces, interact with hydrophobic core so keeps them in place.
-Eg channel and carrier proteins
What are channel proteins?
Transmembrane proteins that allow specific molecules to pass through cell membrane FACILITATED DIFFUSION.
No energy needed to function
What is a carrier protein?
Transmembrane protein that binds to the molecule its transporting and causes it to undergo conformational changes FACILLITATED DIFFUSION. Requires energy
What are glycoproteins?
Intrinsic proteins that have attached carbohydrate(sugar) cahins of varying lengths and shapes.
Play a role in cell adhesion(when cells join to form tight junctions at tissues)
Act as receptors for chemical signals
What are glycolipids?
Similar to glycoproteins, lipids with attached carbohydrate(sugar).
These molecules are called cell markers/antigens and can be recognised by the immune system as ‘self’
What 2 factors affect membrane structure?
Solvents and temperature
Why does temp affect membrane structure?
Phospholipids are constantly moving, higher temp=more kinetic energy=faster movement=more fluid/increased permeability
If temp too high it will break down
Carrier and channel proteins will denature, involved in transport across memb, so permeability affected
Why do solvent affect membrane structure?
Water is a polar structure and is essential in the formation of the phospholipid bilayer, heads face towards, tails face away.
Many organic solvents are less polar than water eg alcohols, will dissolve memb, this is why alcohol is used in antiseptic wipes(dissolve bacteria memb)
