Tutor profile: Kyle R.

When placed in an aqueous solution, purified phospholipids can spontaneously assemble into enclosed, spherical lipid bilayers resembling cell membranes. Explain why this happens.

The spheres formed by purified phospholipids are called "Micelles". This is a phenomenon that happens with phospholipids and a commonly observed example of this is oil and water. Oil, when in water will form spheres exclusive of water. This occurs as phospholipids possess a hydrophobic (water hating/repelling) fatty acid tail as well as a hydrophilic (water loving/attracting) head. The hydrophobic tails will congregate together to remove water between them, reaching a state that is most energetically favorable while having the hydrophilic heads face outside as they prefer interacting with water.

Describe the normal function of potassium channel during an action potential.

The potassium channel is a fundamental channel in maintaining the electrochemical gradient across the phospholipid bilayer in cells. This gradient is created by the Sodium-Potassium Pump (Na+/K+), which functions by utilizing ATP to pump 3 sodium outside of the cell and 2 potassium into the pump creating a negative charge on the inside of the cell. When an action potential has been triggered, potassium ion channels open to allow an influx of potassium back into the cell, allowing for quick repolarization of the cell.

Antarctic fish have a higher percentage of unsaturated phospholipids and fewer cholesterol molecules in their membranes compared to warm water fish. Explain how do these changes in membrane lipid composition help Antarctic fish survive in very cold temperatures?

In cold temperature environments, cell membranes will require enhanced fluidity to compensate for the reduced fluidity caused by a cold environment in this case, cells will produce higher levels of unsaturated fatty acids and reduced cholesterol into the cellular membrane to restore fluidity. When these fish are transferred to a warmer environment, more saturated fatty acids, fatty acids with longer tails, and cholesterol will be added to the phospholipid bilayer to increase membrane rigidity.