Quiz 4 Flashcards
The __ amino acids share a common structure but differ in their ____
20, side chains
amino acids contain a central
tetrahedral a-carbon atom
_____ link amino acid residues in a ______
peptide bonds, polypeptide
some amino acid side chains contain ___ who’s ___ values may vary
ionizable groups ; pka
all amino acids are built on a central
tetrahedral a-carbon
The amino acid is tetrahedral
around the alpha carbon, except fir proline [and uncommon derivatives] , all of the amino acids commonly found in proteins possess this type of structure
amino acids are sorted into groups based on their side chains
- non polar amino acids
- polar uncharged amino acids
- charged acidic amino acids
- charged basic amino acids1
non polar amino acids
- leucine
- alanine
- proline
- valine
- methionine
- phenyl alanine
- isoleucine
- tryptophan
polar amino acids
- glycine
- serine
- asparagine
- glutamine
- threonine
- cysteine
- tyrosine
charged acidic amino acids
- aspartic acid
- glutamic acid
charged basic amino acids
- lysine
- arginine
- histidine
at neutral pH…
the a-carboxyl group and the a- amino group are charged
a-carboxylic group pKa
2
a-amino group pKa
9
aspartic acid
Asp, D, pKa(B-carboxyl)= 3.9 (-) at pH 7
glutamic acid
Glu, E, pKa(y-carboxyl)= 4.1(-) at pH 7
histidine
His, H, pKa(imidazole)= 6.0 neutral at pH 7
Cysteine
Cys, C, pKa(sulfhydryl SH)= 8.4 neutral at pH 7
tyrosine
Tyr, Y, pKa(phenolic OH)=10.5 neutral at pH 7
lysine
Lys, K, pKa(E-aminp)=10.5 (+) at pH 7
arginine
Arg, R, pKa(guanidino group)=12.5 (+) at pH 7
amino acids and many other biological compound are chiral molecules whose
configurations can be depicted by Fischer projections
the amino acids in proteins all have the
L stereochemical configuration
all amino acids [with the exception of glycine] are
chiral, not symmetric at the a carbon
D,L nomenclature is based on
D- and L- glyceraldehyde
Absorb UV
Tyr and Trp
- absorbance at 280 nm is a good diagnostic test for amino acids
amino groups from Schiff bases and
amides
carboxyl groups form amides and
esters
edmans reagent
reacts with the a-amino group of an amino acid or peptide to produce a phenylthiohydantoin, or PTH derivative
Lys residues can form
disulfides and can easily be alkylated
edmans reagent react with the
N-terminal amino acid of a peptide or protein to form a cyclic thiazoline derivative that reacts in weak aqueous acid to yield a PTH-amino acid, plus the polypeptide with a new N-terminus
GFP
green fluorescent protein is a naturally fluorescent protein , can be used to tag virtually any protein, structure or organelle.
- lies in center or b barrel protein structure
