Ch 5 Amino Acids - Biochemistry

general pKa of carboxy group of aa

2.9

general pKa of amino group of aa

9.5

pI

• pH at which molecule has a net zero charge

• taken by averaging the 2 pKa’s flanking the section in the graph where the molecule has a net 0 charge

aromatic amino acids

W, Y, F

pKa

pH at which molecule DEprotonates

7 ionizable aa’s

DEHCYKR

“Don’t Express Hate, Create Your Kindness, Right?”

Which pKa’s do you take into account when calculating the charge of a polypeptide?

• N-terminus (~9.5)

• C-terminus (~2.2)

• R groups of the (7) ionizable aa’s, if present

  • pKa will be given in table

amphoteric

acidic and basic properties

T/F? Proteins are amphipathic and amphoteric.

True

amphipathic

having hydrophilic/polar and hydrophobic/nonpolar properties

T/F? The location of functional groups (R groups) are the basis

for protein function.

True

T/F? Dr. Howerton groups Y as nonpolar.

True

Glycine is the only ___ and therefore ___ aa.

chiral; symmetrical

Which amino acids are synthesized during translation, specifically while on tRNA?

Selenocysteine (Sec) & pyrrolysine (Pyl)

Which amino acids are a result of post-translational modifications?

• Phosphoserine

• 4-Hydroxyproline

• N-e-acetyllysine

• y-carboxyglutamate

What does acetylation of Lys play a role in?

gene expression/suppression

Post-translation modification functions

• signaling pathways

• Ca2+ binding

• stabilizing structures, eg. collagen

• gene expression or suppression

Essential aa’s (9)

MILKFTW HV

T/F? Peptide bond formation requires energy and releases water, thus it is a condenstation reaction.

True

Peptide bonds are shorter than ___ but longer than ____.

shorter than C-N (single bonds);

longer than C=N (double bond, not amide)

Most constrained aa

Proline

Peptide bond is rigid due to ____

resonance