Question

What are four major functions of membrane proteins? How are membrane proteins inserted into the membrane - give details of two methods. Give a specific example of a protein that is an integral membrane protein. How can we determine from gene sequence information whether the protein will be an integral membrane protein?

Answer 1

• Functions of membrane proteins: 1. Membrane proteins act as carriers for transporting molecules across the membranes by active, passive and facilitated transport. Besides, they act as pumps that actively transport ions across the membrane.

2. They act as cell adhesion molecules that anchor cells to neighbouring cells or to basal lamina.

3. They functions as enzymes, catalyzing the reaction at the surface of the membrane.

4.They act as receptors for cell-signaling, neurotransmitters and hormones.

• Membrane proteins can be inserted into the membrane by two methods- 1. Co-translational translocation: In this way the trans-membrane proteins are inserted across plasma membrane one or several times until is interrupted by amino-terminal sequence. 2. Post-translational translocation: After translation the nascent proteins are modified as needed, then transported to plasma membrane by post translational system.
• Example of integral membrane protein: 1. Glycophorin 2. Cell adhesion proteins such as integrins, cadherins
• Each integral membrane proteins have specific orientation and that is determined by specific amino acid sequences and these amino acid sequences are determined by gene sequence information.