Amin Acid-Base Flashcards
what happens to COOH group when pH = pKa
- protonated (neutral) and deprotonated (negative) are equal > each COOH is -0.5
what happens when pH < pKa
pH > pKa
- whatever is protonated will be protonated > +1
- whatever is deprotonated will be deprotonated > -1
very low pH: charges usually positive
very high pH: charges usually negative
What does horizontal component of titration curve?
- pkA value is midpoint of horizontal segment
- acidic FG is donating protons to molecules of the base, neutralize to prevent pH from increasing
- Buffering
What amino acids have 3 pKa values?
Lysine, Glutamate, Histidine
- charged amino acids
what is basic def of pKa
- how likely something is to give up proton
H-H equation? at what equation is pH = pKa
pH = pKa + log A-/HA
- when acid and base are equal, log(1) = 0
- 50% prot and 50% deprot
What is approx pKa of D and E?
Asp and Glut
- 3-4
what is approx pKa of H, L, R in that order?
His: 6
Lys: 11
Arg: 12.5
What is usually the first point on a titration curve strong base and weak acid?
- 1/2 equiv point
- horizontal plateau region 50% protonate and deprotonate, thus neutral charge
- pH = pKa1
- buffering region, midpoint of vertical section
What is the second point on a simple titration curve?
- all the protons from COOH are being used to buff the base
- 1 mol of base used to remove all acidic protons of COOH functional group
What is third point on simple titration curve?
pI: where pH is neutral
- not basic enough to protonate amine group
4th point on simple titration curve?
2nd pKa = pH
- 100% ionization of amine group
- 2nd mol of base used to remove 1 mol of acid
what is happening at pH > pKa2
- too basic, deprotonating and charge will be negative
where is pI of acidic and basic amino acids?
acid: average 2 lowest pKas
base: average 2 highest pKas
what is the equivalence point?
when mol of acid = mol of base
- funcitonal group fully ionized
- mid piont of vertical region
