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The features of this model provide evidence for which explanation of why all growing strands are synthesized in a 5′ to 3′ direction? The two strands need to be antiparallel to bond properly

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marianaegarciaperedo

DNA strand must be synthesized in direction 5'-3'. The phosphate group, attached to the 5′ carbon of the dTMP, forms a covalent bond with the oxygen atom attached to the 3′ carbon of the growing strand  (Option D).

Among the enzymes involved in the DNA replication process, one of them is DNA polymerase III.

DNA polymerase III

  • Responsible for DNA elongation by adding nucleotides to the growing chain, from 3' to 5' extremes.

  • It includes only nucleotides that complement the original strand.

  • DNA polymerase recognizes the primer and starts the synthesis from there.

  • The four dNTPs are used as the substrate for the synthesis of the new chain.

Let us remember that the deoxyribonucleotides triphosphate are

- dATP

- dGTP

- dCTP

- dTTP

  • During the synthesis, a phosphate group is transferred and the 3'-OH group behaves as a nucleophile in the 3' extreme of the growing chain.

  • The reaction occurs on the phosphate group of the new dNTP, releasing inorganic pyrophosphate.

  • A free 3'-OH group is always required to add a new dNTP. This is why DNA synthesis must occur from the 5' extreme to the 3' extreme ⇒ to leave a free OH-group

Options:

A)  The two strands need to be antiparallel to bond properly.

B)   Thymine and adenine would not bond properly if the strand grew from 3′3′ to 5′5′.

C)   The translation of mRNAmRNA occurs in the 5′5′ to 3′3′ direction; therefore, the growing DNADNA strand must also grow in the 5′5′ to 3′3′ direction.

D)   The phosphate group, attached to the 5′ carbon of the dTMP, forms a covalent bond with the oxygen atom attached to the 3′ carbon of the growing strand.

The correct one is option D. The free OH group of the growing chain must join the phophaste group of a new dNTP.

You can learn more about DNA replication process at

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