Question

Lecture 4. Interfacial phenomena and membranes

• How are proteins positioning themselves on the surface of membranes?
• What are liposomes, how are they prepared and for what purposes are they used?
• Which factors of phospholipids are important in determining the fluidity of membranes?
• What are the differences between the phospholipids?
• What are the causes of structural bending of the membrane

Answer 1

How are proteins positioning themselves on the surface of membranes?

Integral membrane proteins, also called intrinsic proteins, have one or more segments that are embedded in the phospholipid bilayer. Most integral proteins contain residues with hydrophobic side chains that interact with fatty acyl groups of the membrane phospholipids, thus anchoring the protein to the membrane.

What are liposomes, how are they prepared and for what purposes are they used

Lysosomes - Little Enzyme Packages

The purpose of the lysosome is to digest things. They might be used to digest food or break down the cell when it dies. ... The Golgi then does its final work to create the digestive enzymes and pinches off a small, very specific vesicle. That vesicle is a lysosome.

Lysosomes are surrounded by a membrane composed of phospholipids that separate the inside of the lysosomes from the membrane's external environment. Phospholipids are the same cellular molecules that make up the cell membrane surrounding the entire cell. Lysosomes range in size from 0.1 to 1.2 micrometers. Structurally, lysosomes are like a floating garbage bag that contains enzymes capable of digesting molecules. Their external membrane is like a gateway that allows molecules inside of the lysosome without allowing the digestive enzymes to escape into the cell.

The lysosome membrane helps to keep its internal compartment acidic and separates the digestive enzymes from the rest of the cell. Lysosome enzymes are made by proteins from the endoplasmic reticulum and enclosed within vesicles by the Golgi apparatus. Lysosomes are formed by budding from the Golgi complex

• Which factors of phospholipids are important in determining the fluidity of membranes?

Factors that influence bilayer fluidity

• The length of the fatty acid tail. The length of the fatty acid tail impacts the fluidity of the membrane. ...
• Temperature. As temperature increases, so does phospholipid bilayer fluidity. ...
• Cholesterol content of the bilayer. ...
• The degree of saturation of fatty acids tails.
• What are the differences between the phospholipids?
• Phospholipids are similar to triglycerides, but they do vary slightly in form and function. While triglycerides have glycerol and three fatty acids, phospholipids have glycerol, two fatty acids and a phosphate. Phosphates are molecules with charges and have oxygen and phosphorus.

  Phospholipids of a lipid bilayer can be divided in to two groups:

• Those derived from glycerol - phosphoglycerides.
• Those derived from sphingosine - sphingomyelin.
• What are the causes of structural bending of the membrane ?

  Membrane bending caused by proteins that directly deform cellular membranes. Many processes in the cell require proteins that shape membranes

• Second, membrane morphology and dynamics can also be affected by the heterogeneous distribution of some lipids within a bilayer.