What is the basis for the difference in how the leading and lagging strands of dna molecules are synthesized?
a. the origins of replication occur only at the 5′ end.
b. helicases and single-strand binding proteins work at the 5′ end.
c. dna polymerase can join new nucleotides only to the 3′ end of a pre-existing strand.
d. dna ligase works only in the 3′ -> 5′ direction

c. DNA polymerase can join new nucleotides only to the 3′ end of a pre-existing strand.

Explanation:

The double stranded molecule of DNA having the pairing strands in the anti-parallel condition. One strand is remain in configuration as the 5’ to 3’ end, the complementary strand is positioned 3’ to 5’ end.

New DNA strand synthesis occurs from the 3’ to 5’ end as the enzyme DNA polymerase attach itself to the 3’ end of a DNA strand. It will add new nucleotides to the 3' end of the DNA.

Hence, the option (c) is the correct answer.

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i guess you forgot putting it.