Question

1. what signal on a protein allows cells to target this protein to the right location?

2. how do cells distinguish sensory vs transmembrane pretty?

3. what are the major functions of ER

4. what control the fluidity of plasma membrane? why cholesterol can help maintain the integrity of the cell membrane ?

Answer 1

1. Targeting signals or targeting peptides present in form of polypeptide chains allow cells to target respective proteins to the right location.

2. Cells have different kinds of receptors for detecting the signal of different proteins. Hence cells can distinguish between any proteins with help of their receptors.

3.ER have long tubular structure so they mainly transport proteins to the other orgenelles of cell. They provide skeletal framework to the cell and serve as major area for cellular reactions. ER also help in synthesis of proteins, and other nutrients required by the cells.

4. Many factors control the fluidity of plasma membrane like lipids amount, composition and chains whether long or short,temperature etc. Higher temperature makes the membrane more viscous.

Cholestrol can maintain integrity of cell membrane because at high temperature cholestrol will melt and will provide viscosity whereas at low temperature it will enter amidst the phospholipid layers maintaining their softness and fluidity and protecting membrane from getting stiff or rigid.