McMurry (Kap. 19,2) Flashcards
According to the Henderson-Hasselbach equation, if:
- The pH of a solution is known.
- The pKa of an acid is known.
We can calculate the [base] and [acid] in the solution.
See page 684-685 for tutorial of how to find it for alanine at pH=9.
83% of alanine molecules in 1M solution are neutral, and 17% are deprotonated taken pKa2 reaction into account.
Page 684-685.
In the titration curve for the amino acid (alanine) is plotted using the henderson hasselbach equation on page 685.
See the tutorial for how its done on the same page:
1.leg: pH 1-6
2.leg: pG 6-11
see page 685.
In the titration curve, it can be seen that in the acidic solution the amino acid is in protonated form, and in basic solution is in deprotonated form.
In between the two is an intermediate pH at which the amino acid is balanced between anionic and cationic forms and exist as the neutral zwitterionic form.
this pH is called the amino acids isoelectric point (pI)
correct.
The different pI values for the different amino acids can be found in page 680-681.
The (pI) value depends on the structure of the amino acid.
How are they catagorized?
15 neutral amino acids = pH range from 5-6,5 near neutrality.
2 acidic amino acids = lower pH, so the deprotonation of the side chain doesnt occur at pI.
3 basic amino acids = higher pH, so the protonation of the side chain doesnt occur at their pI.
Just as individual amino acids have pI values, thus does proteins because of the accumulative pI of the amino acids.
What are some examples?
lysozome (predominance of basic amino acids - therefore a higher pI value = 11).
Pepsin (predominance of acidic amino acids - therefore a lower pI value = 1)
How does the solubility of the protein get affected by the pI value?
Solubility in water is usually lowest at the (pI) where the protein has no net charge.
Higher solubility when pH is higher/lower then the (pI-value) where the protein is charged.
Can the different solubilities of the protein in different pI values get taken advantage of?
Yes - electrophoresis technique.
to seperate a mixture of proteins ito its pure constituents.
Se page 687 for explanation.
