Question

A membrane consisting only of phospholipids undergoes a sharp transition from the crystalline form to the fluid form as it is heated. However, a membrane containing and 80% phospholipid and 20% cholesterol undergoes a more gradual change from crystalline to fluid form when heated over the same temperature range. Explain why. Purification of transmembrane proteins requires the addition of detergents to the buffets in order to solubilize the proteins. (a) Why would transmembrane proteins be insoluble if the detergent were not present? (b) Draw a schematic diagram that shows how the detergent sodium dodecyl sulfate interacts with a transmembrane protein. Identify each type of lipid-linked protein in the following drawing. Fig 2 Use Equation 9-4 to calculate the free energy change for the movement of Na+ into a cell at the resisting potential (described in problem 1). Assume the temperature is 37 degree C. Is this process favorable? The concentration of Ca^2+ in the endoplasmic reticulum (outside) is 1 mM, and the concentration of Ca^2+ in the cytosol (inside) is 0.1 Pm. Calculate G at 37 degree C when the membrane is a) -50 mV (cytosol negative) and (b) +50 mV. In which case is Ca^2+ movement more potential thermodynamically favorable? A high fever can interfere with mal neuronal activity. Since temperature is one of the terms in Equation 9-1, which defines membrane potential, a fever could potentially alter a neuron's resting membrane potential.

Answer 1

Ans 9) The change in the rigid, gel like plasma membrane to the free flowing fluid like plasma membrane is known as phase transition and the temperature at which this occurs is known as transition temperature.

As the cholesterol is added, it will interfere with the fatty acid chain movement which results in less fluidity i.e it will require more temperature to convert from rigid to fluid form as compared to the plasma membrane having only phospholipids.