Class 2 : Cell membranes Flashcards
Name 4 functions of cell membranes.
- Keep constant the ion content of the cytoplasm
- Prevent the loss of critical cellular material
- Prevents the loss of ATP
- Maintains interaction of the cell with its environment
Describe the structure of the cell membrane.
Bilayer of phospholipids within which protein and cholesterol molecules are embedded.
According to the fluid mosaic model : the plasma membrane is composed of phospholipids within which membrane proteins are able to move laterally - in a highly controlled fashion.
Total thickness is 8-10 nm (therefore, TEM is required to explore the details).
What are lipid rafts?
A grouping of proteins, along with cholesterol that forms a dense part of the membrane and is generally going to allow for some kind of signalling to happen.
What are the 2 types of lipid rafts?
- Planar/ flotillin lipid rafts : recrute integral proteins for signalling
- Caveolar/caveolin lipid rafts : contain integral caveolins protein which are associated with vesicular formation.
What are the 2 types of membrane proteins ?
- Integral (transmembrane proteins that pass through the lipid bilayer) They can be single pass or multipass.
- Peripheral (not embedded in the lipid bilayer i.e. located outside).
What are the 6 categories of integral membrane proteins ?
- Pumps
- Channels
- Receptors
- Linker proteins
- Enzymes
- Structural proteins
Describe glycocalyx and its functions.
The glycocalyx is a carbohydrate coat on the outside of the membrane
Its consists of carb portions of glycoproteins and glycolipids that are embedded in the plasma membrane.
Different types of cells have different level of glycocalyx
Many tissue and cell type-specific antigen are located in this tissue (e.g. MHC, blood group antigens…enzymes involved in the digestive process)
Enterocytes have a very thick glycocalyx!
It has the capacity to shape the plasma membrane ! Bipolymer concentration in the glycocalyx affects the overall shape of the cell.
Distinguish linker proteins from structural proteins?
Linker (e.g. integrins) : They interact w/ extracellular matrix and they link w/ actin filament of the cell. Essential for cell-cell interaction.
Structural protein : form junctions with neighboring cells - they are not quite linker proteins because they anchor across 2 different cells. They are likely to be found on the basolateral surface.
What is the role of cholesterol in membrane fluidity?
Cholesterol prevents tight packing so the membrane can maintain some fluidity.
It acts as a structural buffer for unsaturated fatty acids.
Prevent membrane freezing in cold temperature and limits excessive fluidity in warm temperatures.
Name 3 features of the membrane that provide its fluidity
- Loose attachment of the phospholipids, proteins and carbs
- Chemical structure of the phospholipids
- Presence of cholesterol
Increasing the relative proportion of phospholipids with unsaturated tails results in:
A more fluid membrane.
Cell can do this own their own if required!
Name 3 types of membrane transports and briefly explain what they do.
- Simple diffusion (allow diffusion of fat soluble uncharged molecules through concentration gradient)
- Carrier proteins (transfer small water-soluble molecule in a highly selective process, some by active transport some by passive transport)
- Channel protein (a regulated process - i.e. something will stimulate the channel to open or close)
Voltage gated ion channels , ligand gated ion channels and mechanically gated ion channels are examples of :
Transport proteins called channel proteins.
They need a stimuli to open such as membrane potential, neurotransmitters, mechanical stress.
Name the 3 different types of vesicular transport.
- Endocytosis
- Exocytosis
- Transcytosis
Endocytosis is referred to as cell drinking. Uptake of fluid and macromolecules by endocytosis can involves 3 different mechanisms. Name them :
- Pinocytosis (2 pathways : micropinocytosis and macropinocytosis)
- Phagocytosis
- Receptor-mediated endocytosis
