Question

Provide an example for each of the three types of lipids and state one structural difference and one function for each type of lipids.

Answer 1

Background information

Lipid:

• It is a class of compounds, are insoluble in water but are soluble in other organic solvents.
• They serve a variety of vital functions in living organisms. a) They are act as chemical messengers, b) serve as valuable energy sources, c) provide insulation, and d) main components of membranes.
• Fats, phospholipids, steroids, and waxes they are major gropus of lipids.

Ans

• Fat:

Structure: A fat molecule consists of two kinds of parts: a glycerol backbone and three fatty acid tails. Glycerol is a small organic molecule with three hydroxyl (OH) groups, while a fatty acid consists of a long hydrocarbon chain attached to a carboxyl group. A typical fatty acid contains 12–18 carbons, though some may have as few as 4 or as many as 36.

Function: vitamins (A, D, E, and K) are fat-soluble, meaning that they must be associated with fat molecules in order to be effectively absorbed by the body. eg. Beta carotene is an important antioxidant. Fats also provide an efficient way to store energy over long time periods, since they contain over twice as much energy per gram as carbohydrates, and they additionally provide insulation for the body.

H-C-OH H-C-OH Fatty Acid HO-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C -H (three of these, may have ifferent stvuctures)

• Phospholipids

Structure: A phospholipid is composed of two fatty acids, a glycerol unit, a phosphate group and a polar molecule. The phosphate group and polar head region of the molecule is hydrophillic (attracted to water), while the fatty acid tail is hydrophobic (repelled by water). When placed in water, phospholipids will orient themselves into a bilayer in which the nonpolar tail region faces the inner area of the bilayer. The polar head region faces outward and interacts with the water.

Function: Phospholipids are a major component of cell membranes, which enclose and protect the cytoplasm and other contents of a cell. They are also a major component of myelin, a fatty substance that is important for insulating nerves and speeding up electrical impulses in the brain.

Phosphate CH2 CH CH2 O C Glycerol LPhospholipid bilayer Saturated fatty acid Hydrophobic tail Unsnurated tatty acid Hydrophilic head group

• Steroids

Structure: Steroids have a carbon backbone that consists of four fused ring-like structures. Although they do not resemble the other lipids structurally, steroids are included in lipid category because they are also hydrophobic and insoluble in water. All steroids have four linked carbon rings and several of them, like cholesterol, also have a short tail. Many steroids also have an –OH functional group attached at a particular site, as shown for cholesterol below; such steroids are also classified as alcohols, and are thus called sterols.

Function: Steroids include cholesterol, sex hormones (progesterone, estrogen, and testosterone) produced by gonads and cortisone.

н,с CH3 н,с CH3 CH3 но Cholesterol он но Cortisol

• Wax

Structure: Waxes are composed of an ester of a long-chain alcohol and a fatty acid.

Function: Wax covers the feathers of some aquatic birds and the leaf surfaces of some plants, where its hydrophobic (water-repelling) properties prevent water from sticking to, or soaking into, the surface.