Why can't adenine bind to cytosine as IT binds to thymine? look at - ProProfs Discuss
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Why can't adenine bind to cytosine as it binds to thymine? Look at the structures of adenine and cytosine.



A. Cytosine has the wrong sugar ring, so it cannot be linked to adenine.
B. The partial charges are not opposites, so no hydrogen bonds can form.
C. The size of cytosine is different from the size of thymine, so the double helix would be kinked.
D. Cytosine is facing the opposite direction from thymine, so adenine cannot bind it.
E. Cytosine cannot form hydrogen bonds, but thymine can.

This question is part of DNA: The Molecule of Heredity quiz
Asked by RiseAsOne, Last updated: Nov 01, 2019

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2 Answers

A. Lucius

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A. LuciusSenior Content writer, Diploma in Literature, Dover, Delaware
Senior Content writer, Diploma in Literature, Dover, Delaware

Answered on Nov 01, 2019

The correct answer to this question is option C – The partial charges are not opposites, so no hydrogen bonds can form. The oxygen and nitrogen present in nitrogenous bases are electronegative atoms. Electronegative oxygen and nitrogen atoms that have free lone pair have potential of accepting hydrogen bonds (hydrogen bond acceptors). DNA nucleotides have the potential to form hydrogen bonds will complementary nucleotides.

For instance, guanine and cytosine form nitrogenous base pair because of their complementary (3) hydrogen bond donor and hydrogen bond acceptors. This makes both nucleotides complementary to one another. Same goes for adenine and thymine, they pair by hydrogen bond donors and acceptors. They have only 2 hydrogen bonds between them.

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RiseAsOne

RiseAsOne

Answered on Dec 12, 2017

The partial charges are not opposites, so no hydrogen bonds can form.
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