CSIR NET JRF notes MCQ on Basic biology Answer


1. What name can be given to glucose, fructose and galactose?

The correct answer was Monosaccarides

All three (glucose, fructose and galactose) contain 6 oxygen atoms, 6 carbon atoms and 12 hydrogen atoms. However, all are arranged differently and have different shapes.All three are soluble in water.

2. It is widely known that the building blocks of proteins are amino acids. What reaction allows several amino acids to join together to form a protein?

The correct answer was Condensation reaction

In a condensation reaction, water is removed and a peptide bond forms between the amino group of one amino acid and the carboxyl group of another.It is the order of amino acids which determines the structure and function of the protein.Carbohydrates and triglycerides also arise from the joining of molecules via condensation reactions.

3. Many people talk about "good" and "bad" fats. What must a fat contain to be classed as a "good" fat?

The correct answer was At least one C=C double bond

If a fat/lipid contains at least on C=C double bond, it is classified as an unsaturated fat, and will usually be liquid at room temperature.Triglyceride molecules consist of one molecule of glycerol bonded to three fatty acids by ester bonds. Each fatty acid contains an "R" group which is a hydrocarbon chain which determines whether the fat is saturated or unsaturated.

4. When using Biuret's test, which macromolecule will produce a positive reaction (colour change from blue to lilac)?

The correct answer was Protein

Biuret's solution typically consists of equal amounts of sample and sodium hydroxide with 5 drops of copper sulphate solution.When testing for a fat the emulsion test is carried out. The sample is dissolved in ethanol and if the solution becomes cloudy when added to water a fat is present.

Benedict's test will show a brick red precipitate in the presence of a reducing sugar (glucose, fructose, galactose, maltose or lactose).Iodine is used to test for the presence of starch which turns the iodine black/blue.

5. After eating proteins, fats or carbohydrates, they must be digested as they are large insoluble molecules and so cannot be absorbed into the blood stream. Enzymes catalyse the breakdown of these molecules into smaller soluble molecules. Which macromolecule would be most likely to bind with endopeptidase?

The correct answer was Protein

Endopeptidase is one of the three main enzymes which catalyse the breakdown of proteins into amino acids. Endopeptidase is produced in the stomach and the pancreas and breaks long chain polypeptides into shorter chains.

The clue is in the name endoPEPTIDase as it is peptide bonds which join amino acids together.

6. Once digested, fats, proteins and carbohydrates eventually enter the bloodstream. Which of the following recombine to form chylomicrons in epithelial cells of the small intestine before eventually entering the bloodstream via the subclavian vein?

The correct answer was Fatty acids and glycerol

Fats are churned and heated in the stomach, emulsified by bile secreted by the gall bladder and then broken down by lipase secreted by the pancreas.After forming chylomicrons they diffuse into a lacteal and are transported to the subclavian vein.

7. Which macromolecule's functions include insulation, waterproofing, energy storage and shock absorption?

The correct answer was Fats

It is well known that respiration typically involves the oxidation of glucose, however when glucose is in short supply triglyceride molecules can be broken down. These yield about 3 times more energy that glucose.

8. Which carbohydrate is a long unbranched chain of beta-glucose molecules, which is indigestible to mammals?

The correct answer was Cellulose

Glycogen and starch are both made from alpha-glucose molecules.The difference between alpha and beta-glucose molecules is small but significant. The -H and -OH groups in a beta-glucose molecule swap positions relative to in an alpha-glucose molecule.

9. Animal cell membranes are mainly composed of a phospholipid bilayer. What happens to a triglyceride to form a phospholipid?

The correct answer was Loss of one fatty acid and gain of one inorganic phosphate groupAlthough the "phosphate head" of a phospholipid is water soluble (hydrophilic) the "fatty acid tail" is insoluble (hydrophobic) and so the phospholipid bilayer provides a barrier to polar, water soluble molecules.

Although water molecules are polar, they are small enough to slip between phospholipids and so enter the cell.

10. There are 20 naturally occurring amino acids and the many combinations of these monomers gives rise to a huge number of proteins, all with different functions. One use of proteins in the human body is as enzymes. Which of these bonds holds an enzyme in its tertiary structure?

The correct answer was Hydrogen bonds

Disulphide bridges, ionic bonds and Van der Waals' forces also keep the enzyme in its shape.The reason enzyme shape is so important is because each enzyme has a complimentary shape to a particular substrate.Hydrogen bonds are also the bonds between water molecules and are what keep two strands of DNA together.