question_answer

Directions : (1 - 5)

Case Based MCQs

Case I : Read the passage given below and answer the following questions.

The sequence of bases along the DNA and RNA chain establishes its primary structure which controls the specific properties of the nucleic acid. An RNA molecule is usually a single chain of ribose-containing nucleotide. On the basis of X-ray analysis of DNA, J.D., Watson and F.H.C. crick (shared noble prize in 1962) proposed a three dimensional secondary structure for DNA. DNA molecule is a long and highly complex, spirally twisted, double helix, ladder like structure. The two polynucleotide chains or strands are linked up by hydrogen bonding between the nitrogeneous base molecules of their nucleotide monomers. Adenine (purine) always links with thymine (pyrimidine) with the help of two hydrogen bonds and guanine (purine) with cytosine (pyrimidine) with the help of three hydrogen bonds. Hence, the two strands extend in opposite directions, i.e., are antiparallel and complimentary.

In the following questions (Q. No. 1-5), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage.

Assertion : DNA molecules and RNA molecules are found in the nucleus of a cell.

Reason : There are two types of nitrogenous bases, purines and pyrimidines. Adenine [A] and guanine [G] are substituted purines; cytosine [C], thymine [T] and uracil [U] are substituted pyrimidines.

A) Assertion and reason both are correct statements and reason is correct explanation for assertion.

B) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

C) Assertion is correct statement but reason is wrong statement.

D) Assertion is wrong statement but reason is correct statement.