Question

In a DNA molecule, the phosphate group is attached to ______ carbon of the sugar residue of its nucleotide and ______ carbon of the sugar residue of the next nucleotide by ______ bonds.
A. 5',3',phosphodiester
B. 3',5',phosphodiester
C. 5',3',glycosidic
D. 3',5',glycosidic

Answer 1

Nitrogen base pair, sugar residue and phosphate group combinely formed nucleotide by glycosidic and phosphodiester bond.so we have to identify the linkage or bonding of phosphate group with its molecule to another nucleotide present beside it and so on.

Complete answer:
• With the help of this study, Watson and Crick (1953) proposed a double helix model for DNA. For this model Watson, Crick and Wilkins were awarded the Nobel Prize in 1962.
• One main hallmark (main point) of the double helix model is complementary base pairing between purine and pyrimidines.
• DNA-DNA is composed of two polynucleotide chains according to the model given by Watson and crick.
• Both polynucleotide chains are complementary and antiparallel to each other.
• In both strands of DNA the direction of phosphodiester bond is always the opposite manner. i.e. If the direction of the phosphodiester bond in one strand is 3-5 then it is 5-3’ in another strand.
• Both strands of DNA are held together by hydrogen bonds. These hydrogen bonds are always present between nitrogen Bases of both strands of DNA.
• Adenine binds to thymine by two hydrogen bonds whereas cytosine binds to guanine by three hydrogen bonds, it is the ultimate truth.
• In a DNA molecule, one purine always pairs with a pyrimidine. For which an approximately uniform distance Between the two strands of DNA is generated.
• In a DNA plane one base pair stacks over the other in a double helix. This, in addition to H-bonds, counters stability Of the helical structure of DNA.
• So it concludes that one phosphate group is attached to the 5’position of its molecule and 3’position of the next nucleotide molecule by a phosphodiester bond.

Hence, the correct answer is option (A).

Note: We have to know the details linkage or bonding of the phosphate group with the own nucleotide and the next nucleotide thoroughly so we can answer this type of questions easily. remember that if 5 ends of its own molecule then others have it opposite i.e. 3 must be. It also follows in case of identification of coding and noncoding strands.