Question
Following are the statements with reference to lipids. [NEET 2021]
I. Lipids having only single bonds are called unsaturated fatty acids.
II. Lecithin is a phospholipid.
III. Trihydroxy propane is glycerol.
IV. Palmitic acid has 20 carbon atoms including carboxyl carbon.
V. Arachidonic acid has 16 carbon atoms.
Choose the correct answer from the options given below
(a) I and III
(b) III and IV
(c) II and III
(d) II and V
Answer/Explanation
Ans. (c)
Statements I, IV and V are incorrect, while II and III are correct. The incorrect statements can be corrected as Lipid having only single bonds are called saturated fatty acids. Palmitic acid has 16 carbon atoms including carboxyl carbon. Arachidonic acid has 20 carbon atoms.
Question
Which of the following are not polymeric ? [NEET 2017]
(a) Nucleic acid
(b) Proteins
(c) Polysaccharides
(d) Lipids
Answer/Explanation
Ans. (d)
Among the given options except lipids all are polymers. These are formed by the polymerisation of monomers. The basic unit of lipid are fatty acids and glycerol molecules that do not form repetitive chains. Instead they form triglycerides from three fatty acids and one glycerol molecules.
Question
A typical fat molecule is made up of [NEET 2016, Phase I]
(a) One glycerol and three fatty acid molecules
(b) One glycerol and one fatty acid molecule
(c) Three glycerol and three fatty acid molecules
(d) Three glycerol molecules and one fatty acid molecule
Answer/Explanation
Ans. (a)
A typical fat molecule is triglyceride formed by esterification of one glycerol and three fatty acid molecules. The three fatty acids can be of same type or different depending on the type of the fat molecules.
Question
A phosphoglyceride is always made up of [NEET 2013]
(a) only a saturated fatty acid esterified to a glycerol molecule to which a phosphate group is also attached
(b) only an unsaturated fatty acid esterified to a glycerol molecule to which a phosphate group is also attached
(c) a saturated or unsaturated fatty acid esterified to a glycerol molecule to which a phosphate group is also attached
(d) a saturated or unsaturated fatty acid esterified to a phosphate group, which is also attached to a glycerol molecule
Answer/Explanation
Ans. (c)
A fat is formed of two kinds of smaller molecules, i.e. glycerol and fatty acids. In making a fat free fatty acid molecules join to glycerol by an ester linkage. A fatty acid has a long carbon skeleton, usually 16 or 18 carbon atoms in length. If there are no double bonds between carbon atoms composing the chain, then as many hydrogen atoms as possible are bonded to the carbon skeleton. This is called saturated fatty acid. Unsaturated fatty acid has one or more double bonds. Phosphoglycerides are esters of two fatty acids, phosphoric acid and a trifunctional alcohol glycerol. The fatty acids are attached to the glycerol at the 1 and 2 position on glycerol through ester bonds.
Question
Which one of the following is not a constituent of cell membrane? [CBSE AIPMT 2007]
(a) Cholesterol
(b) Glycolipids
(c) Proline
(d) Phospholipids
Answer/Explanation
Ans. (c)
The lipids of cell membrane are of three types namely phospholipids, glycolipids and sterols. The sterol found in the membrane may be cholesterol (animals), phytosterol (plants) or ergosterol (microorganisms). Cell membrane is made up of lipid+protein $(60 \%)$ and carbohydrates $(2-10 \%)$. Proline is an amino acid.
Question
Lipids are insoluble in water because lipid molecules are [CBSE AIPMT 2002]
(a) hydrophilic
(b) hydrophobic
(c) neutral
(d) Zwitter ions
Answer/Explanation
Ans. (b)
Bloor (1943) first time used the term ‘lipid’. These are the compounds of $\mathrm{C}$, $\mathrm{H}, \mathrm{O}$ but the ratio of $\mathrm{H}$ and $\mathrm{O}$ is more than $2: 1$ that is the ratio of oxygen is lesser as compared to carbohydrates. Lipids are insoluble in water but soluble in non-polar solvents such as benzene, chloroform, etc. Common lipid occurring in a cell is phospholipid. It contains a hydrophilic (polar) head and a hydrophobic (non-polar) tail.
Question
Which steroid is used for transformation? [CBSE AIPMT 2002]
(a) Cortisol
(b) Cholesterol
(c) Testosterone
(d) Progesterone
Answer/Explanation
Ans. (b)
Cholesterol forms a major component of animal cell membranes liposomes (artificially created spheres surrounded by a phospholipid bilayer like a membrane) which are used for transformation (transgenics).
Question
Spoilage of oil can be detected by which fatty acid? [CBSE AIPMT 2001]
(a) Oleic acid
(b) Linolenic acid
(c) Linoleic acid
(d) Erucic acid
Answer/Explanation
Ans. (d)
Erucic acid occurs as glycerides in vegetable oils. It is a monounsaturated omega-9-fatty acid. It is found in rapseed, mustared seed and wallflower seed.