Question

A membrane spanning protein that is a channel for potassium ion transport is made up of six copies of a single polypeptide. Potassium ions are transported across the membrane using the channel.  What types of amino acids do you expect to find on the potassium ion channel polypeptides next to the heads of the membrane lipids? (multiple answers)

	a.	Nonpolar
	b.	Positively charged
	c.	Polar
	d.	Negatively charged

Answer 1

ANSWERS : b. positively charged

c. polar.

EXPLANATION : It's due to phospholipids bi-layer structure. It has head (hydrophillic ) and tail ( hydrophobic).Intrinsic/integral membrane proteins that are embedded in the hydrophobic region of the lipid bilayer, transmembrane proteins that span across the membrane, and extrinsic or peripheral membrane proteins that associated weakly with hydrophillic tail.

Intrinsic membrane proteins present at heads of the lipid posses negatively charged phosphate groups. This makes condition energetically favourable for proteins to have positively charged amino acids as they can form ionic bonds, also polar amino acids as they can form hydrogen bonds in environment.

Non polar (hydrophobic aminoacids ) amino acids are expected to present near tail as they are favourable for hydrophobic environment

Negatively charged amino acids ,ends [COOH]are unbalanced, and they are acidic.These amino acids are also polar and therefore hydrophilic