Question

Create some drawings/models of membrane transport proteins. Blob models are fine but they should be annotated as instructed below. In your drawing include a model for a lipid bilayer clearly showing the polar and non-polar nature of the lipid components. The models of the proteins should include annotation/shading or other indication that indicates the types of amino acid functional groups you might expect to see in (a) the exterior of the protein in contact with the lipid bilayer, (b) the regions of the exterior part of the protein that interacts with the lipid polar groups, (c) and some attempt to illustrate the types of residues one might expect to find in the core of the protein (depending on substrate being transported. Also indicate whether the protein should act as a channel (passive no need for external energy) or pump (active and requiring the coupling of an energy source). Do this for: (1) a hypothetical protein that transports Cl- ions down/with their chemical gradient and (2) a transporter of glucose up/against the chemical gradient. Explicitly note if each reaction being catalyzed is exergonic or endergonic and depict it in a reaction coordinate diagram.

Answer 1

Chloride moves down the concentration grandient by passive transport through Chloride channels. No energy is consumed in this process.

Glucose is transported (for example in intestinal cells) up the concentration grandient by acitve transport through sodium glucose cotransporter proteins. In this, alongwith glucose, sodium moves down its concentration grandient to generate energy to drive the process. This process is endergonic(G >0).

Charged amino acids are found on the exterior part of the membrane transport protein in contanct with the lipid bilayer; non-polar amino acids are found in exterior of the transport protein in contact with the lipid polar head and polar amino acids are found in the core of the protein.