Biochem 153A: Week 2 Discussion

I. Technical Details
Amino acid quiz
This week's GSPS will address microenvironmental effects on pKa an PI calculations
neon.chem.ucla.edu/~wong/153A.html and voh.chem.ucla.edu/153A-1 (or 2)

II. Biochemical Equilibria
Objectives: Know your pKa's; understand microenvironmental effects on pKa; how to use the Henderson-Hasselbalch equation; how to calculate isoelectric point

Determining the Isoelectric Point of a solution
1) Break down the question
2) Draw the structure as it would appear at pH 0. Everything is protonated.
3) Add the pKa's
4) Draw a quick titration curve and/or chart the deprotonations
5) Find the point in the titration where you have 100% of the neutral zwitterion
6) Calculate the midpoint between the two pKa's surrounding this particular point

Questions:
1) What is a zwitterion?
2) What is PI?
3) How can amounts of glycine species be determined at any point in a titration experiment?
4) What species of the tripeptide lysylprolylaspartate are present at pH 7.0? What are the fractions of each species at any given point in a titration of this molecule? What is the PI of a solution containing this tripeptide?
5) Dissolve 5g of lysine (MW= 128.17) in 50 ml of water and titrate it with 1 M NaOH (MW=40.00). How much base is required to reach the isoelectric point?

II. Primary Structure: Amino Acid Sequence
Objectives: Understand how resonance plays a role in amino acid properties and peptide bond planarity; be able to draw amino acids in a polypeptide backbone; understand directionality of polypeptide drawing and naming; understand formation of peptide plates