Cell Membranes 5.1 Flashcards
Why do we have membranes?
For compartmentalisation which is why we have membrane-bound organelles. it keeps them all separate so they can each have their own optimum conditions to carry out their function
What is the plasma membrane
The membrane that separates the cell from the external environment
What is the structure of membranes?
They have a phospholipid bilayer so have hydrophilic phosphate heads on the outside of both layers and a hydrophobic core in the middle
Why do we have a phospholipid bilayer?
It is used because we have an aqueous environment inside and outside the cell, so the hydrophilic heads can react with the water, while the hydrophobic core keeps the two aqueous environments separate.
What is the model of the phospholipid bilayer?
It’s the fluid mosaic model which is that the phospholipids can move within the layer so the membrane is fluid, and there are many types of proteins embedded in the membrane so it’s like a mosaic.
What is present in the plasma membrane?
hydrophilic heads, hydrophobic core, cholesterol, glycoproteins, glycolipid, extrinsic protein, intrinsic protein, pores
Intrinsic Proteins
Proteins that are embedded in both layers of the phospholipid bilayer, they have hydrophobic R-groups on the outside so that they can be embedded in the hydrophobic core.
Types of intrinsic proteins (transport)
Channel proteins have hydrophilic R-groups on the inside which let polar molecules diffuse through the channels.
Carrier proteins are also intrinsic proteins and are involved in active transport.
Types of intrinsic proteins (receptors)
Glycoproteins are intrinsic proteins that have a carbohydrate chain attached and they act as cell receptors for cell signalling
Glycolipids are lipids with a carb chain attached and they act as cell markers so they can be recognised as cell-own during an immune response
Cell signalling
When chemicals bind to glycoproteins that act as receptors and can send signals for a direct response or series of reactions to occur, it’s a way for cells to communicate.
Extrinsic proteins
Proteins present on the outer layer of the membrane only. They have hydrophilic R-groups on the outside that can interact with the phosphate heads.
Cholesterol
This is a sterol that has a hydrophilic alcohol end as well as a hydrophobic lipid end. It is positioned between the phospholipids in the bilayer and maintains the fluidity of the membrane, but also adds stability.
