Test: Introduction & Structure of Nucleotide - Grade 12 MCQ

Purines have two rings in their structure, but pyrimidine bases have only one ring.Adenine has two rings in its structure.

Thymine is present in DNA but not in RNA.

Option A: Sugar component of a nucleotide is ribose. This statement is true for RNA nucleotides. However, for DNA, the sugar is deoxyribose, not ribose.

Option B: Sugar component of a nucleotide is deoxyribose. This statement is true for DNA nucleotides, but not for RNA nucleotides.

Option C: The bases in nucleotides are attached to a pentose sugar moiety by a glycosidic linkage. This statement is universally true for all nucleotides, whether in DNA or RNA. The nitrogenous base is attached to the sugar molecule via a glycosidic bond.

Option D: The sugar molecule of the nucleotide is in L-configuration. This statement is false. The sugar in nucleotides is in the D-configuration.

The correct answer is:

Option C: The bases in nucleotides are attached to a pentose sugar moiety by a glycosidic linkage.

A nucleoside is composed of a base and a sugar.

A nucleotide is composed of a base, a sugar and a phosphate.

In DNA and RNA, the phosphodiester bond is the linkage between the 3' carbon atom of one sugar molecule and the 5' carbon atom of another, deoxyribose in DNA and ribose in RNA

Ribose or deoxyribose is a 5 carbon sugar.

5’-phosphate group of one nucleotide unit is joined to the 3’-hydroxyl group of the next nucleotide.

Purines have two rings in their structure, but pyrimidine bases have only one ring is true.

Purines and pyrimidines are two types of nitrogenous bases that are found in DNA and RNA. Purines have a larger, more complex structure than pyrimidines and contain two rings of atoms in their structure. Pyrimidines, on the other hand, have a simpler structure and contain only one ring of atoms.

Statements 1: They are hydrophobic and relatively insoluble in water at the near-neutral pH of the cell and 2: At acidic or alkaline pH the bases become charged and their solubility in water decreases are both false. Purines and pyrimidines are polar molecules and are generally soluble in water. They are not hydrophobic and do not become less soluble in water at acidic or alkaline pH.

Statement 3: At acidic or alkaline pH the bases become charged and their solubility in water increases is also false. As mentioned above, purines and pyrimidines are polar molecules that are generally soluble in water. They do not become more soluble in water at acidic or alkaline pH.

Therefore, the correct answer is statement 4: Purines have two rings in their structure, but pyrimidine bases have only one ring.

Nucleotides are the building blocks of nucleic acids.