Cell surface membrane and transport. ch4 Flashcards
how do phospholipids form a membrane?
The hydrophillic heads interact with the H₂O outside and inside the cell and the hydrophobic tails interact with each other. This forms the formation of the phospholipid bilayer
how is the structure of a cell membrane described
it is described as a fluid-mosaic structure.
why is it described as a fluid mosaic structure
Because a mosaic is different pieces coming together to form art( randomly scattered) and the proteins and the phospholipds are free to move around. (imagine plastic balls floating on a pool. They aren’t in a fixed position, they move about.
Explain how the arrangement of phospholipids affect their fluidity
when they are closely packed, the membrane becomes less fluid. Due to them being packed, the permeability of the cell is reduced. The membrane becomes very rigid, hence, if pressure is applied it may snap.
if they are loosely packed, or far apart from each other, the membrane becomes more fluid. Because of the large gaps, the hydrophobic interaction between the tails may be too weak and it can easily break apart.
Optimum fluidity is when the membranes arent too packed and arent too loose. This means it will produce a characteristic known as partially-permeable. And when pressure is applied, due to its flexibility, it is able to bend, hence, it will not break.
explain how temperature affects membrane fluidity
When temperature is increased , the phospholipids move further apart due to their increased KE, thus increasing fluidity.
If temperature is reduced, the KE of phospholipids will decrease, thus, they become more tightly-packed, meaning, less fluidity.
explain how the length of fatty acid tails affect the membrane fluidity
When the tails of the fatty acids are long, they become tangked and this restricts phospholipid movement. This decreases the fluidity of the membrane.
when the tails are short, they are able to move around freely, thereby increasing fluidity.
explain how the type of fatty acid tail affects the membrane fluidity
There are two types of fatty acids, and they are
saturated and unsaturated fatty acids
when it is saturated, the structure is linear, when it is unsaturated, the structure bends (due to the double bonds between carbon atoms).
If they are saturated, they are packed more closely (less fluidity) but when they’re unsaturated, they are packed less closely (more fluidity)
explain the structure of cholestrol
cholestrol is a type of lipid
with a hydrophillic head and only 1 hydrophobic tail.
what is the role of cholestrol in cell surface membrane?
it maintains the membrane fluidity.
how does cholestrol maintain membrane fluidity?
If the cell becomes too cold, the phospholipds will try to come close to each other, but cholestrol pushes them away and prevents is from being tightly packed.
if the cell becomes too hot, phospholipids will try to move further apart, but the cholestrol tells them to come back and prevents it from being loosely packed
How i easily memorize this:
imagine the weather is cold and youre in a couple, but there’s a third wheel. when you guys are trying to snuggle each other, the third wheel tries to separate you guys so they wont feel left out
Also imagine youre in a heated argument with your partner, you guys will definitely not want to be near each other, but a mediator will come and advice you guys to come back together. So in these scenarios, the cholestrol is the 3rd wheel and the mediator as well.
what is the size of the phospholipid bilayer?
7nm
when asked to draw the fluid mosaic membrane structur, what are the key features you must include
- the phospholipids
- cholestrol
- Membrane proteins (intrinsic and extrinsic)
- you can also add the glycolipds and glycoproteins
explain the function of the membrane proteins (intrinsic and extrinsic) (1)
Sometiimes, due to the nature of the phospholipid bilayer, some molecules are unable to enter the cell. To solve this, some of the membrane proteins may act as a transport protein. (channel and carrier proteins). They allow the molecules to pass through either by diffusion or active transport
function of membrane proteins
(2)
A receptor protein is just a protein to receive a signalling molecules eg: hormone
Glycoproteins also acts as receptor proteinis by receiving signalling molecules like hormones
function of glycolipids and glycoproteins
cell to cell recognition: the most significant importance of c-t-c recognition is immune responses. it enables you to distinguish what is familiar and what is different
