Ask A Scientist© Molecular Biology Archive

name         laura
 status       student
age          17
Question -   the differences between amino acids

First, what they have in common is the basic structure HXN-CHR-CO2H.  The
differences are the substituent groups N and R.  For most of the twenty
common biological amino acids, X = Hydrogen.  The R groups are what set them
apart.  In one of the common biological amino acids, proline, the R group
curls around and connects to the N atom, so the substituent "X" is the end
of the R group.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
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Imagine amino acids as pieces of a jigsaw puzzle.  Each of the pieces can
be described mostly the same way -- squarish cardboard with a piece of a
picture on one side.  But to put the puzzle together, the differences
between the pieces become important.  All those indentations and
projections tell you where each piece fits into the whole thing.

In chemical terms, amino acids can be described much the same way.  They
have a general structure made of nitrogens and carbons that is used to link
amino acids together to build proteins.  The unique feature is a
hydrocarbon sidechain which can be as chemically simple as a single
hydrogen atom (the Glycine below), or as complicated as a carbon ring
structure (Tryptophan).  (If the diagram on the right doesn't have two
rings with 6 and 5 points each, try realigning the font in courier.)  The
catch here is that the protein can still be put together and look okay, but
it may not work right.

Glycine                                   Tryptophan

  -O H                                       -O H
   | |                                        | |
O=C-C-NH3+                                 O=C-C-NH3+
     |                                          |
     H                                    C   H-C-H
                                         / \    |
                                        C   C - C
                                        |   |   |
                                        C   C   C-H
                                         \ / \ /
                                          C   N
                                              |
                                              H

---------
Christine Ticknor
Ph.D. Student
Yale University
New Haven, Connecticut
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Hi Laura!
The amino acids are the monomeric units that make the proteins.
They all contain both a basic group (-NH2) and an acidic group
(-COOH). So they are amphotheric compounds.
All amino acids have 2 important structural features in common:
they are all alfa-amino acids and with the exception of glycine
(whose molecules are achiral), almost all naturally occcurring
amino acids have the L-configuration at the alfa-carbon.
OK...that are the similarities. And about the differences?
Let's see...if you consider their general formula to be:
(NH2)- (R)- (COOH)
R can be different organic  radicals more or less complicated.
and it is possible to classify
the amino acids upon what is R:
R group is neutral
R contains an -OH group
R contains Sulfur
R contains a carboxyl group
R contain a basic amino group

Of course it results all have different molecular weights and
different physical, chemical and biochemical  properties.
OK?
Thanks for asking NEWTON!
Mabel
(Dr.Mabel Rodrigues)
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