Chapter 4- Amino Acids Flashcards
pKa of primary amine
~9
pKa of the carboxyl group
~2
Aliphatic hydrocarbon side chains are typically:
Non polar
Characteristics of Met
- first amino acid in proteins
- participates in hydroponic interactions
- involved in metal binding
Proline is conformationally
constrained (No movement)
nonpolar amino acids are typically found in the ____ of proteins
interior (not exposed to water)
AA’s that have maximum absorbance of 280 nm
Trp and Tyr
Why do Phe, Tyr and Trp absorb strongly in the UV/Vis spectrum?
Their phenyl group
UV/Vis spectroscopy is an
absorption technique (transition from ground state to excited state)
Fluorescence is:
emission of a photon from an excited state to the ground state (shows up in higher wavelengths) (typically lower energy than absorption)
The amino acids in the middle of the protein typically participate in _____ with other side chains
H-bonds
The OH in side chains is
Very reactive
common in enzyme active sites
sites of protein modification
Disulfide bond formation requires an
oxidizing agent (O2, H2O2)
Reducing agents often contain a
Thiol group (SH)
Why can His act as a proton donor and an acceptor?
The pH is so close to the physiological pH
Characteristics of His:
- Can be buried in the protein fore or exposed to solvent
- involved in many enzymatic acid-base reactions
Charged amino acids generally prefer to be on the _______ of proteins in an aqueous environment
surface
Charged amino acids can form
electrostatic interactions (salt bridges)
at physiological pH, the -COOH and -NH2 are
Overwhelmingly ionized
Isoelectric point (pI)
pH where no net electric charge
KI and Kj are
dissociation constants of the 2 ionizations flanking the pI
Deprotonation of amino acids is ordered by
the lowest pKa to the highest pKa
Increased distance from the alpha carbon results in
more basicity (electrostatic influence decreases)
Stabilization/ destabilization is caused by
electrostatic interactions
Hydrophobic interactions can ________ the pKa of acidic residues
raise
Hydrophobic interactions can ________ the pKa of basic residues
Lower
Amino acids are optically active because
the alpha carbon is chiral
All amino acids derived from proteins are in the ___ conformation
L
Post-translation modifications
modification of a standard amino acid happens after the polypeptide chain has been synthesized
