Acid Base Chemistry of Amino Acids. Flashcards
Which functional groups of all amino acids can lose a proton?
The amino and carboxyl groups.
The carboxyl group and the amino group of an amino acid can be considered to be what type of chemical?
They can each be considered to be weak acids.
Why are the carboxyl group and the amino group of amino acids considered to be weak acids?
Because they only partially dissociate in water whereas strong acids completely dissociate.
What does the carboxyl group dissociate to?
COO-.
What does the amino group dissociate to?
NH2.
What is the Ka of an acid?
The dissociation constant.
What is the Henderson Hasselbalch equation?
pH = pKa + log * conjugate base/acid.
What does the pH stand for in the Henderson Hasselbalch equation?
The negative log of the proton concentration.
What does the pKa stand for in the Henderson Hasselbalch equation?
The negative log of the Ka.
What is the Henderson Hasselbalch equation used to determine?
The pH of a solution, once a strong base or acid has been added to it.
The Henderson Hasselbalch equation is particularly useful when creating what kind of solution?
Buffer solutions.
What is a buffer solution?
A solution that resists changes in pH when an acid or base is added to that solution.
How is a buffer solution made?
By mixing a weak acid with its conjugate base.
HA + A-.
The most effective buffer solutions contain what proportion of weak acid to conjugate base?
The best buffer solutions have the same amounts of weak acid and conjugate base.
Are all buffer solutions effective at any pH?
No, buffer solutions are only effective at a certain pH.
What is the buffering range of a buffer solution?
The pH range at where the buffer is effective.
What is the usual buffering range of a buffer solution?
The pKa of the acid + or - 1.
What would be the buffering range for an acid with a pKa of 2.8?
The buffering range would be between 1.8 and 3.8.
What happens when pH of the solution is equal to the pKa of the acid?
Exactly 1/2 of the molecules are in a dissociated form and exactly 1/2 are undissociated.
If HA is the acid and A- is a base that is added to the acidic solution, what will happen?
HA goes to A- and H+.
When Ph of solution = pKa of the acid there are equal amounts of HA and A- with H+.
As more base is added there will be no more HA and the solution will be A- and H+.
When is an acid or base at its best as a buffer?
When pH = pKa.
This is because large amounts of acid or base can be added to the solution without significantly changing the pH of the solution.
How many pKs do the non-polar and the polar uncharged amino acids have?
2 pKs.
How many pKs do the acidic and basic amino acids have?
3 pKs.
What will the structure of alanine look like at a low pH?
It will be fully protonated.
The amino end will be NH3+.
The carboxyl end will be COOH.
The fully protonated form of alanine has what charge?
+1.
As you increase the pH of the solution containing the fully protonated form of alanine, what will happen?
COOH begins to lose H, forming COO- and H+.
At a pH of 2.3, alanine will exist in 2 forms where 1/2 of the carboxyl groups are COOH and the other 1/2 are COO-.
Describe the pK1 of alanine?
This is when half of the carboxyl group is in COO- and the other half is in the COOH form.
Is alanine a particularly good buffer at pK1?
Yes.
As pH increases in a solution with alanine at pK1, what happens?
The carboxyl end completely dissociates to COO-, this is when alanine reaches its isoelectric point (PI).
What is the isoelectric point of an amino acid?
When the molecule has a net charge of 0.
How do you calculate the PI of an amino acid?
PK1 + PK2 / 2.
Are amino acids good buffers when they are at their isoelectric point?
No. They are the worst buffers at their PI.
What happens to alanine in its isoelectric form if more base is added to the solution?
The amino end will donate a proton to the media going from NH3+ to NH2.
When does alanine reach its pK2?
When exactly half of the amino group is in its NH3+ form and the other half is in NH2 form.
Is alanine a good buffer at pK2?
Yes.
What happens to alanine in its pK2 form if more base is added to the solution?
The NH3+ will completely dissociate to form NH2.
What charge does the completely dissociated form of alanine have?
COO- and NH2 give a charge of -1.
How is the titration of an acidic or basic amino acid differ from a non polar or polar uncharged amino acid?
If adding base to an acidic solution, the carboxyl end will dissociate first to give pK1.
The R group will dissociate 2nd to give pK2.
The amino group will dissociate 3rd to give pK3.
How do you calculate the PI for a basic or acidic amino acid?
Take the 2 pKas that are on either side of the form of the amino acid that has a charge of 0, add them together and divide by 2.
How can water act as a solvent for macromolecules?
By forming hydrogen bonds with them.
What is homeostasis?
When the bodys acid and base levels are normal.
The body is at physiological pH.
What is physiological pH?
7.36 and 7.44.
With extreme ranges of 6.8 - 7.8.
How do the lungs buffer the acid levels in the body?
They remove CO2, which if left in the blood could form carbonic acid.
How do the kidneys buffer the acid levels in the body?
They remove ammonia and H+ which could form ammonium.
