Textbook Notes (290,000)
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BIO130H1 (100)
Chapter 2

BIO130H1 Chapter Notes - Chapter 2: Leucine, Valine, Tryptophan

Course Code
Kenneth Yip

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Amino Acid Basic Structure
Proteins are polymers made of Amino Acid monomers
Each protein has a
unique sequence of amino acids
that gives the
molecule its
unique properties
o Many of the capabilities of a protein can be understood by
examining the chemical properties of its constituent amino
Twenty different amino acids
are commonly used in the
construction of proteins, whether from a virus or a human
There are two aspects of amino acid structure to consider: that
which is
common to all
of them and that which is
unique to each
All amino acids have a
carboxyl group
and an
amino group
, which
from each other by a single carbon atom, the
o In a neutral aqueous solution, the α‐carboxyl group loses
its proton and exists in a negatively charged state (
COO, and the α ‐amino group accepts a proton and exists
in a positively charged state (NH3+)
Carbon atoms bonded to four different groups can exist in two
configurations (stereoisomers) that cannot be superimposed on
one another
o Amino acids also have asymmetric carbon atoms
With the
exception of glycine
, the α‐carbon of amino acids
to four different groups
so that each amino acid can exist in either
a D or an L form
Amino acids used in the synthesis of a protein on a ribosome are
always L‐amino acids
o The selection L‐amino acids must have occurred very
early in cellular evolution and has been conserved for
billions of years
Microorganisms, however, use D‐amino acids in the synthesis of
certain small peptides, including those of the cell wall and several
During the process of protein synthesis, each amino acid becomes
joined to two other amino acids, forming a long, continuous,
unbranched polymer called a Polypeptide Chain
The amino acids that make up a polypeptide chain are joined by
Peptide Bonds that result from the linkage of the carboxyl group
of one amino acid to the amino group of its neighbor, with the
elimination of a molecule of water
o A polypeptide chain is composed of a string of amino acids
joined by peptide bonds
The average polypeptide chain contains about 0 amino acids
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