Question

Bonding between deoxyribose and base in pyrimidine nucleoside molecule is:-
1. 1’- 1’ glycosidic linkage
2. 1’- 6’ glycosidic linkage
3. 1’- 9’ glycosidic linkage
4. 1’- 4’ glycosidic linkage

Answer 1

Hint:-Pyrimidines are heterocyclic compounds which contain a single carbon ring. It also contains two nitrogen bases. In nucleic acid, there are three types of pyrimidine- cytosine, thymine, uracil. Cytosine and thymine are present in DNA whereas uracil is present in RNA.

Complete step-by-step solution:-
DNA and RNA are made up of chains of nucleotides. A nucleoside is a purine or pyrimidine nucleobase that is bound to a pentose sugar, either ribose or deoxyribose. When the phosphate group is bonded to a nucleoside, it forms a nucleotide. Purines are heterocyclic compounds made up of two carbon rings. They include adenine and guanine. Pyrimidine is made up of a single carbon ring and includes cytosine, thymine and uracil. The pentose sugar present in DNA is called deoxyribose where a hydroxyl group is present on the 2’ carbon of the ribose ring but the hydroxyl group is absent in the 2’ carbon of the deoxyribose. A glycosidic linkage is also known as the glycosidic bond and is a type of covalent bond which connects the carbohydrate molecules.
1. 1’- 1’ glycosidic linkage- Deoxyribose through the 1’ carbon is linked to 1’ nitrogen of the pyrimidine through a bond called the glycosidic bond.
2. 1’-6’ glycosidic linkage- 1’ carbon of pyrimidine is bonded to the 6’ nitrogen of the base.
3. 1’- 9’ glycosidic linkage- - 1’ carbon of purine is bonded to the 9’ nitrogen of the base through a glycosidic bond.
4. 1’- 4’ glycosidic linkage- 1’ carbon of deoxyribose is attached to the 4’ of nitrogen of pentose sugar.
The correct answer to the question is 1’- 1’ glycosidic linkage.
The correct answer is option A.

Note:- The phosphodiester linkage is between the 3’ carbon atom of pentose sugar and 5’ carbon atom of another deoxyribose in the case of DNA or RNA molecules. Glycosidic linkage is between two pentose sugars.