Things to think about from Week1

Well, it's been one week in biochem and we're all realizing that, despite the warm weather, it's not summertime anymore. Work hard this quarter and you'll do fine in 153A.

You guys seem to be okay with drawing a titration curve, but I hope you all understand what a titration curve signifies. I know it's taken me a few years to really understand its implications and what information can be derived from a simple titration curve.
I've had various questions in my office hours and discussions that I found worth some extra thought. Some of you won't even blink before coming up with an answer. Don't worry if you do need to, though, just seek help immediately.

1) Why does buffering occur within the specific region pka +/- 1 pH unit?

2) Equivalence point is not the same as Equilibrium

3) Why are water molecules more densely packed when water is in liquid form?

4) If there are 4 pKa's in a molecule, wouldn't the PI simple be at the midpoint between the extreme two pKa's? That is, the very middle of the titration curve?

5) Amino acids, considered singly, are amphoteric. Within the polypeptide, are they still?

6) I had no clue what you were doing at the end of Friday's noon lecture. (Or, if you're in the 9A lecture: What is an isoelectric point?)
My response: All TA's are covering it in discussions and GSPS this week.
Some of you may have caught my boo-boo in calculation at the end.
The main points are still the same: the PI is achieved when we have 100% of a zero net-charged species, which occurs at the midpoint of the two pKa's surrounding that point in a titration.