Lecture 2 handout (17/1 2017).

-philic: friend

-phobic: fearing

Polar: implies a direction of some kind (may be used for e.g. DNA/RNA, H2O or a compound with a charge)

Polar properties of H2O: The unequal sharing of electrons within a bond leads to the formation of an electric dipole (i.e. a separation of positive and negative electric charge)

Lipohilic  hydrophobic  non-polar (these terms may sometimes be used as synonyms)

“Non-polar substances are friends with long aliphatic carbon chains (i.e. lipids) and fears H2O”

Amphi: on both sides, around (e.g. amphibians, amphitheater)

-pathy: feeling: suffering; perception (e.g.: amphipathy, telepathy, sympathy)

acyl group: any group of the form RCO- (R is some type of an organic group)

fatty acid: a carboxylic acid with a long aliphatic carbon chain

Ester bond: esters are chemical compounds consisting of a carbonyl adjacent to an ether linkage. They are derived by reacting an oxoacid (e.g. acetic acid) with a hydroxyl compound (e.g. an alcohol).

Most membrane phospholipids are phosphoglycerides, i.e., esters of two fatty acids, phosphoric acid and a tri-functional alcohol – glycerol. The fatty acids are attached to the glycerol at the 1st and 2nd positions on glycerol through ester bonds. There may be a variety of fatty acids, both saturated and unsatured.The third position contains a phosphodiester bond (the same bond as in DNA/RNA).

The properties of a phospholipid are characterized by the properties of the fatty acid chains and the hydrophilic group. The long hydrocarbon chains of the fatty acids are non-polar. The phosphate group has a negatively charged oxygen to make this group ionic. In addition,a hydrophilic group is attached through the phosphodiester bond, which creates a highly water soluble head of phospholipids.

Comments to slide 11:

The plasma membrane is a lipid bilayer (interspersed with proteins). This is because the amphipathic nature of its phospholipid components that assembles into a double layer - or bilayer - when placed in a polar surrounding, like water.

Fluid mosaic model: A model conceived by S.J. Singer and Garth Nicolson in 1972 to describe the structural features of biological membranes.

The plasma membrane is described to be fluid because of its components (i.e. lipids and membrane proteins) are floating around laterally (a 2D-fluid).

The plasma membrane is termed amosaic because it is composed of many different kinds of macromolecules, such as various phospholipids, glycolipids, cholesterol, integral proteins, and lipoproteins. Since these molecules interacts to different extent  compartmentalization (e.g. within “lipid rafts”, see slide 8 - 11).