Fats and oils can pass directly through the membrane as they are non-polar. For other
substances, there are protein channels specific for different materials. The membrane is
made up of two layers having proteins scattered around in the lipid.
Six major functions of membrane proteins:
● Transport- It allows the transport of different ions/solutes, small molecules.
Note:- There is a group of specific transport proteins for each cell type and physiological
stage.
Transport types:● Passive- purely based on the concentration gradient, hydrophobicity, size and charge
● Active- Solute is moved against the concentration/electrochemical gradient, energy is
needed.
Transport type can also be classified as
Uniport, Symport and Antiport.
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Enzymatic activity- Different enzymes bind to the them and changes conformation or
release signals
Signal transduction- when receptor attaches to membrane proteins, various
molecular are released that helps in signal transduction
Cell-cell recognition
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix (ECM)
Three major classes of membrane proteins:
1. Transporters
2. Ion Channels
3. Receptors
Ion channels- Channel proteins form transmembrane aqueous pores which allow passive
movement of small water-soluble molecules into or out of the cell or organelle.
Note:1. Ion channels are highly selective for specific ions (eg Na+, K+, Ca2+, Cl-)
2. Ion selectivity depends on: diameter, charge and size
Ion channels are not always open, rather they are gated. Their state changes due to change
in the conformation.
1. Voltage gated- membrane potential difference
2. Ligand gated
3. Stress activated