Lippincott CH1: Amino Acids Flashcards
What amino acid point mutation causes Sickle Cell Anemia?
Replacement of polar glutamate with nonpolar valine at the sixth position in the beta subunit of hemoglobin
Explain hydrophobic effect
nonpolar side chains are forced together due to their hydrophobicity
Which uncharged polar side chain amino acids can lose a proton?
cysteine, tyrosine
Which amino acid can form disulfide bonds?
cysteine
Are aspartic acid & glutamic acid protonated at physiologic pH?
No. They are ionized, containing a negatively charged carboxylate group (–COO^-)
Henderson-Hasselbalch equation
pH = pKa + log [A-]/[HA]
when does pH = pKa?
when amount of HA & A- are equal (weak acid/base and its conjugate)
How do you determine whether the acid or base form is predominant in a solution, relative to pKa?
At pH values below the pKa, the protonated acid form is predominant.
At pH values above the pKa, the deprotonated base form is predominant.
What does pKa tell you?
how acidic or not a given hydrogen atom in a molecule is.
What is the isoelectric point?
the pH at which an amino acid is electrically neutral; the sum of positive charges is equal to the sum of negative charges.
How do you calculate isoelectric point?
(average) pI = pKa1 + pKa2 +… /number of pKa
define amphoteric in terms of amino acids
amino acids that can act as an acid or a base (via COO- & NH3+ groups)
pKa of carboxyl group of amino acids?
approx. 2.3
pKa of primary amino group of amino acids?
approx. 9.1
which chiral/optically active form of amino acids are found in humans?
L-form
