One strand of a fragment of duplex dna has the sequence 5’-atcgacctgatc-3’. a) what is the sequence of the other strand in the duplex? b) what is the name of the bond that joins one nucleotide to another in the dna strand? c) is the bond in part (b) a covalent or a noncovalent bond? d) which chemical groups of nucleotides react to form the bond in part (b)? e) what enzymes catalyze the reaction in part (d)? f) identify the bond that joins one strand of a dna duplex to the other strand. g) is the bond in part (f) a covalent or a noncovalent bond? h) what term is used to describe the pattern of base pairing between one dna strand and its partner in a duplex? i) what term is used to describe the polarity of two dna strands in a duplex?

The structure of DNA was solved by Watson and Crick. They proposed the double helical model of DNA.

Explanation:

a) If one strand has the sequence  5’-ATCGACCTGATC-3’ , then the sequence in the other strand will be complementary to this.

As we know A pairs with T and C pairs with G, so the sequence will be as follows: 3'-TAGCTGGACTAG-5'.

b) Nucleotide are the basic repeating units in a nucleic acid. Nucleotide are joined together by phophodiester bonds in each strand.

c) These phosphodiester bonds are covalent in nature.

d) The phosphodiester bond is formed between the phosphate and  deoxy ribose sugar. Both these units form the backbone of DNA. The hydroxyl group of phosphate reacts with 3' carbon of sugar in adjacent nucleotide to form the ester bond.

e) The enzyme responsible for forming the phosphodiester bond between the nucleotide is DNA polymerase.

f) One strand of DNA is joined to the other strand by the hydrogen bonds between nitrogenous bases.

g) These bonds between nitrogenous bases are hydrogen bonds (not covalent). Two hydrogen bonds are formed between A and T and three hydrogen bonds are formed between C and G.

h) The pairing in DNA double helix is called complementary base pairing.

i) The two strands in DNA are anti parallel i.e. one strand runs from 5' to 3' whereas the other strand runs from 3' to 5'.