Assertion (A) All chemicals added to food items are called food preservatives.
Reason (R) All these chemicals increase the nutritive value of the food.
Assertion (A) Preservative are added to food items.
Reason (R) Preservatives inhibit the growth of mircroorganisms.
Assertion (A) Artificial sweeteners are added to the food to control the intake of calories.
Reason (R) Most of the artificial sweeteners are inert and do not metabolise in the body.
In what respect do prontosil and salvarsan resemble. Is there any resemblance between azo dye and prontosil? Explain.
Prontosil, also called sulfamido chrysoidine, trade name of the first synthetic drug used in the treatment of general bacterial infections in humans.
Prontosil resulted from research, directed by German chemist and pathologist Gerhard Domagk, on the antibacterial action of azo dyes. A red azo dye of low toxicity, prontosil was shown by Domagk to prevent mortality in mice infected with Streptococcus bacteria.
The dye was also effective in controlling staphylococcus infections in rabbits. Within a relatively short period, it was demonstrated that prontosil was effective not only in combating experimental infections in animals but also against Streptococcal disease in humans, including meningitis and puerperal sepsis. Structural formula of prontosil is
From the structure of prontosil, it is very clear that it has $-\mathrm{N}=\mathrm{N}$ - linkage. It was discovered that the part of the structure of prontosil molecule shown in box, i.e., p -aminobenzenesulphonamide has antibacterial activity.
Salvarsan is also known as arsphenamine. It was introduced at the beginning of 1910s as the first effective treatment for syphilis. It is an organoarsenic molecule and has $-$As $=$ As$-$ double bond.
Salvarsan and prontosil show similarity in their structure. Both of these drugs are antimicrobials. Salvarsan contains $-\mathrm{As}=\mathrm{As}$ — linkage whereas prontosil has $-\mathrm{N}=\mathrm{N}$ linkage.
Prontosil (a red azo dye) and azo dye both have $-\mathrm{N}=\mathrm{N}-$ linkage.
How do enzymes catalyse a chemical reaction in the living system? Explain drug target interaction taking the example of enzyme as target.
In the catalytic activity, enzymes perform the following two major functions
(i) The first function of an enzyme is to hold the substrate molecule for a chemical reaction. the active sites of the enzymes hold the substrate molecule in a suitable position, so that it can be attacked by the reagent effectively.
The substrate molecules bind to the amino acid residues of the protein present the active site of the enzyme through a variety of interactions such as hydrogen bonding, dipole-dipole interactions, van der Waals' interactions and ionic bonding.
These binding forces should be strong enough to hold the substrate long enough so that the enzyme can catalyse the reaction, but weak enough to allow the products to depart after their formation.
(ii) The second function of the enzyme is to provide functional groups which will attack the substrate to carry out the chemical reaction. This function is carried out by some other amino acid residues of protein present on the active site of the enzyme.
These provide free amino groups to attack the substrate and bring about the chemical reaction. If the amino acid serine is present nearby the substrate held on the active site, then its -OH group is free to act as a nucleophile in the enzyme catalysed reaction.
The part of the amino acid which lies outside the box act as a nucleophile in enzyme catalysed reactions, but the part of the amino acid which is enclosed in the box is involved in the formation of peptide bond in protein molecule.