Monday, September 22, 2008

Chapter 7 (7.1 Notes)


Membranes are of the utmost importance to the cell as a whole, and to many of the organelles contained in the cell, because they act as selective barriers to let in only the substances that each cell or specific organelle needs to function properly.

Membranes are primarily made up of phospholipids and proteins (though carbohydrates are crucial to membranes, too) held together by weak interactions that cause the membrane to be fluid. In the fluid mosaic model of the cell membrane, the membrane is fluid, and the proteins are embedded in or associated with the phospholipid bilayer.

There are both integral proteins and peripheral proteins in the cell membrane.
  • Integral proteins are those that are completely embedded in the membrane, some of which are transmembrane proteins that span the membrane completely.
  • Peripheral proteins are loosely bound to the membrane's surface.
Carbohydrates on the membrane are crucial in cell-cell recognition (which is necessary for proper immune function) and in developing organisms (for tissue differentiation). Cell surface carbohydrates--many of which are oligosaccharides--vary from species to species and are the reason that blood transfusions must be type-specific.

Notes from the book:
  • Like all biological membranes, the plasma membrane exhibits selective permeability; that is, it allows some substances to cross it more easily than others.
7.1: Cellular Membranes are fluid mosaics of lipids and proteins
  • A phospholipid is an amphipathic molecule, meaning it has both a hydrophilic region and a hydrophobic region (In a phospholipid, the head is hydrophilic, and the the tail is hydrophobic).
Membrane Models: Scientific Inquiry
  • Lipids and proteins have the ability to drift laterally within the membrane.
The Fluidity of Membranes
  • A membrane remains fluid as a temperature decreases, until finally the phospholipids settle into a closely packed arrangement and the membrane solidifies.
  • The membrane remains fluid to a lower temperature if it is rich in phospholipids with unsaturated carbon tails. Because of kinks in the tail where double bonds are located, unsaturated hydrocarbons cannot pack as closely together and this makes the membrane more fluid.
  • **Cholesterol, which is wedged between phospholipid molecules in the plasma membranes of animal cells, can be thought of as a "temperature buffer" for the membrane, because it hinders the close packing of phospholipids, lowering the temperature required for the membrane to solidify.**

This diagram explains membrane protein functions. You may want to look over synthesis of membrane components and their orientation on the resulting membrane.


SMABiology said...

Fantastic. you got the essence of the the fluidity concept of the membrane. The functions of proteins was an added bonus.

Leigh said...

This is just beautiful Jennifer! Thanks for the notes from the book... very helpful :)