Unit 1- Membrane Structure

Question 1

How are cytoplasmic proteins soluble?

Answer 1

The surface of the protein has a greater proportion of hydrophilic R groups on the surface and during post translational modification charged groups such as phosphates can be added to make the surface more hydrophilic.

Question 2

What molecules can pass straight through the bilayer in the membrane and why?

Answer 2

Carbon dioxide and oxygen as they are small and non-polar so will not be repelled by the hydrophobic tails of the phospholipids.

Question 3

Define and describe integral proteins

Answer 3

These penetrate the hydrophobic interior of the phospholipid bilayer and are folded so that they have regions of hydrophobic R groups. These can then form strong hydrophobic interactions tethering the protein to the tails of the phospholipids in the membrane’s interior. These proteins can extend partly into the bilayer or span the width of the membrane (transmembrane proteins).

Question 4

Define and describe peripheral proteins

Answer 4

These are not embedded in the phospholipid bilayer. Instead they form weak bonds with the surface of the membrane. This can either be with the heads of the phospholipids or more commonly with the exposed parts of integral proteins. Some peripheral proteins on the inside of the membrane are attached to the cytoskeleton, which helps to give mechanical support and shape to the cells.