Chapter 4: Amino Acids Flashcards
What are proteins?
Natural products containing nitrogen
All proteins are composed of what?
20 Amino Acids
The building blocks of protein?
Amino Acids
The common amino acids are known as? Why? Which are an exception to this?
-α-amino acids
-because they have a primary amino group (—NH2 ) as a substituent of the α carbon atom
-The sole exception is Proline, which has a secondary amino group
(—NH—), although for uniformity we will refer to proline as an α-amino acid.
How do amino acids differ?
Different side chains also known as R groups
Draw and describe the general structure of an amino acid?
R
I
H2N—–C—–COOH
I
H
Why are Amino Acids Dipolar Ions?
Have at least 2 charges. Amino(NH3+) and Carboxyl (COOH-) are charged
=neutral
An amino acid can act as both? Why
Acid and Base,
Because at physiological pH (∼7.4), the amino groups are protonated and the carboxylic acid groups are in their conjugate base (carboxylate) form
What is a dipolar ion/zwitterion?
amino acids that bear charged groups of opposite polarity
Structure of a dipolar amino acid?
R
I
H3N+—–C—–COO-
I
H
amino acid is pos or neg?
positive
carboxyl pos or neg?
neg
low pH =
(3 names)
cationic, (+), acidic, fully pronated
high pH=
(3 names)
anionic, basic, unpronated
The process of amino acids forming chains with a peptide bond is known as?
condensation reaction
What is a condensation reaction?
bond formation with the elimination of a water molecule
The bond between amino acids?
Peptide bond
3 steps in condensation reaction
take oh from carboxyl group in one amino acid
take h from amine group in other amino acid
creating elimination of water
3 types of amino acids side chains?
Nonpolar, Uncharged polar, and charged polar R groups
Why do the pK values of ionizable groups differ between free amino acids and amino acid residues in polypeptides?
they depend on environment
all amino acids but _____ are chiral
glycine because it has 2 Hydrogens
What is a polarimeter?
device used to measure optical rotation
which amino acids recovered from polypeptides are optically active?
all except glycine
is optically active asymmetric or symmetric?
asymmetric
what does chiral mean
-when four different groups are bonded to the a-carbon atom
-chiral compounds have non superimposable (non identical) mirror images
what are the two mirror image forms of a chiral called?
L isomer
D isomer
or called enantiomers
Glycine has how many H atoms attached to its a-carbon atom?
2, making it superimposable/mirror image/not optically active
Fischer convention is used for what
to describe the different forms of chiral molecules or asymmetric centers
Chrirals rotate
the plane of polarized light
Fischer projections
simpler ways to represent the complex chiral 3D molecules
horizontal bonds extend ?
above/out the plane of the paper,
vertical bonds extend?
below/in the plane of the paper
Modified amino acids occur when?
after protein has been made “post translational modification”
Amino acid modification include the simple additions of what?
additions of small chemical groups to certain amino acid side chains: hydroxylation, methylation, acetylation, carboxylation, and phosphorylation.
Amino acid modification include the simple additions of what?
additions of small chemical groups to certain amino acid side chains: hydroxylation, methylation, acetylation, carboxylation, and phosphorylation.
what’s unique about Individual amino acids and their derivatives?
they have diverse physiological functions. Such as gluthiaone which plays a role in cellular metabolism.
What is an isoelectric point?
The pH at which a molecule carries no net electric charge
pk1= what group? pH around?
pk2= what group? pH around?
pk1=carboxylic group pH around 2.2
pk2=α-amino groups pH around 9.4
free amino acids in solution at neutral pH?
dipolar ions/zwitterions
cysteine can form what kind of bonds
disulfide bonds (SH-) is attached to the side chain
protein(peptide) chain starts with what and ends with what?
starts with amino end
ends with carboxylate
What is the RS system?
In the Cahn–IngoldPrelog or RS system, the four groups surrounding a chiral center are ranked according to a specific, though arbitrary, priority scheme: Atoms of higher atomic number rank above those of lower atomic number (e.g., —OH ranks above —CH3).
What is the RS system?
configuration classification Atoms of higher atomic number rank above those of lower atomic number (e.g., —OH ranks above —CH3).
Amino acids are chiral molecules. Only blank-amino acids occur in proteins (some bacterial peptides contain D-amino acids).
L
