Chapter 3-Amino Acids and Peptides Flashcards
How many amino acids are found in proteins?
20
General structure of an amino acid consists of:
amino group and carboxyl group that are both bonded to the alpha carbon
amino group
NH2 group
carboxyl group
-COOH functional group that dissociates to give -COO minus and H ion
sterochemistry
branch of chemistry that deals with the three d shape of molecules
side chain group
portion of amino acid that determines its identity
chiral
non-superimposable mirror images
what is the amino acid that lacks a chiral center (aka achiral)
glycine
stereoisomers
molecules that differ from each other only in their configuration (3D shape); aka optical isomers
L- and D-amino acids
amino acids whose stereochemistry is the same as the stereochemical standards L- and D-glyceraldehyde
L- amino on left
D- amino on right
What form are the amino acids in proteins?
L
List the non polar hydrophobic amino acids.
Methionine Tryptophan Phenylalanine Isoleucine Leucine Proline Alanine Valine Glycine
List the polar uncharged amino acids.
Threonine Cysteine Tyrosine Serine Asparagine Glutamine
List the acidic amino acids.
aspartic acid
glutamic acid
List the basic amino acids.
Histidine
Lysine
Arginine
alipathic
absence of benzene ring or related structure
proline is often called
imino acid
is an indole ring aromatic?
yes
which is a stronger acid: phenol or alipathic alcohol
phenol
what forms disulfides
thiol groups in cysteine
disulfide bridges are formed in what type of reaction
oxidation reduction
when a carboxyl group loses a proton what forms
carboxylate anion
hydroxyproline and hydroxylysine are found in
collagen
thyroxine
- differs from tyrosine in that it has an extra iodine containing aromatic group on the side chain
- produced by thyroid gland only
- formed by post-translational modification of modification of tyrosine residues in thyroglobulin
zwitterion
electrically neutral (equal positive and negative charges)
neutral amino acids do not exist in the form….
without charged groups
what does a titration curve indicate?
the reaction of each function group with hydrogen ion
diprotic
two protonated groups
electrophoresis
method for separating molecules on the basis of ratio charge to size
isoelectric pH (pI)
- a pH at which the molecule has no net charge
- molecule will not migrate an electric field
pI equation
=pKa1 + pKa2
_________
2
what type of bond links amino acids (very general)
covalent
residues
portions of monomer units included in polymers after splitting out water between the linked monomers
peptide bond
amide bond between amino acids in a protein
steps:
- two amino acids
- water removal
- formation of CO-NH bond
peptides
molecules formed by linking two to several dozen amino acids by amide bonds
amide
name for a compound formed by the reaction between an amino group and a carboxyl group
polypeptide chain
backbone of protein; formed by linking amino acids by peptide bonds
the _____ of the peptide bond lead to a planar group
resonance structures (because of the double bond in the resonance structure there really is no significant rotation)
direction of a peptide chain
N—->C
peptides can play a role in?
hormones
non polar side chains contain:
mostly alipathic or aromatic hydrocarbons
amino acids that have electrically neutral polar side chains containing of
electronegative atoms: sulfure, oxygen & nitrogen
which two amino acids have carboxyl groups in their side chains?
glutamic acid and asparatic acid
