Question #dcae6

FULL QUESTION

http://ocw.mit.edu/courses/biology/7-016-introductory-biology-fall-2014/exams/MIT7_016F14_Prac_Exam_1Sol.pdf

For Question Number 1 Part B. Can the alcohol group (OH) interact to a Lone oxygen atom #O^(-)# with hydrogen bonding?

Please explain why part B is hydrogen bonding interaction.

As you know, hydrogen bonding is a special case of the more general dipole-dipole interactions characterized by a covalent bonding that takes place between a hydrogen atom and three of the most electronegative atoms in the periodic table, oxygen, nitrogen, and fluorine.

This pairing between hydrogen and three of the most electronegative elements gives molecules the possibility of forming hydrogen bonds.

However, molecules that do not contain such a covalent bond can still act as either hydrogen bond acceptors or hydrogen bond donors.

The interaction between the negative charge located on the phosphate group and the positive charge located on #NH_3^(+)# results in an ionic interaction.

However, the electrostatic attraction between the negative charge present on the oxygen in the side-chain of #"Glu"^(150)# and the partial positive charge that exists on the hydrogen in the hydroxide group belonging to the ribose sugar is not great enough to create an ionic interaction.

This happens of course because you don't have a full positive charge on the hydrogen atom.

However, a hydrogen bond will most definitely form.

A lone pair of electrons present on the oxygen atom in the #"Glu"^(150)# will interact with the partial positive charge formed on the hydrogen of the #"OH"# group.

The oxygen atom acts as a hydrogen bond acceptor, and the #"OH"# group acts as a hydrogen bond donor.

Because it lacks a bond to a hydrogen atom, the oxygen belonging to the side-chain of #"Glu"^(150)# cannot donate hydrogen bonds, but it can readily accept them.

This is not the case for the side-chain of #"Tyr"^(201)#. The #"OH"# group belonging to the side-chain can both donate and accept hydrogen bonds. The same can be said for the #NH_2# group.

Read more about hydrogen bond donors and acceptors here:

http://socratic.org/questions/do-ethers-and-esters-form-hydrogen-bonds-with-water-and-with-themselves