Question

Lipids are very diverse in both their respective structures and functions. These diverse compounds that make up the lipid family are so grouped because they are insoluble in water. They are also soluble in other organic solvents such as ether, acetone, and other lipids. Lipids serve a variety of important functions in living organisms. They act as chemical messengers, serve as valuable energy sources, provide insulation, and are the main components of membranes. Major lipid groups include fats, phospholipids, steroids, and waxes.​

Q1 Theory: Describe the basic structure of Phospholipids and Sphingolipids. What functions do these lipids have in living organisms?

(250 words)

Answer 1

The structure of Phospholipids: Phospholipids are compound lipids that are found mainly in cell membrane. A phospholipid is basically an amphipathic molecule that consists of

a. Glycerol backbone

b. Two hydrophobic (non polar) fatty acid tails

c. One hydrophilic (polar) head (phosphorylated head) : The phosphate group in head can be modified by attaching to the alcohol moieties e.g. choline (phosphatidylcholine), ethanolamine (phosphatidylethanolamine), or serine (phosphatidylserine).

The hydroxyl group of C-1 and C-2 of glycerol are esterified to the carboxyl group of two fatty acid chain R1 and R2 and the C-3 is esterified to phosphoric acid.

X = choline, ethanolamine or serine etc.

Function of Phospholipids:

i) Phospholipids are the major component of cell membrane. Due to the amphipathic nature they form the lipid bilayer of cell membrane.

ii) The lipid bilayer acts as a protective barrier to the cell.

iii) It is a selectively permeable barrier which allow certain molecules e.g. water, O2 and CO2 to cross the membrane freely but large molecules cannot pass in this way.

iv) The protein molecules associated with phospholipid cell membrane helps in signal transduction pathway.

The basic structure of Sphingolipids: Sphingolipids are class of lipids that consists of

a. Sphingosin: A sphingoid base with 18 carbons, form a long unsaturated hydrocarbon chain.

b. Fatty acid chain.

In the hydrophobic region shingosin is linked to the acyl group of fatty acid chain via an amide group. The hydrophilic region (R) can be H (ceramide), phosphocholine (sphingomyelin) etc.

Function of sphingolipids:

i) It acts as a protective barrier as a componenent of the ccell membrane.

ii) Participates in signalling pathways.