Acid Base Chemistry of Amino Acids.

Question 1

Which functional groups of all amino acids can lose a proton?

Answer 1

The amino and carboxyl groups.

Question 2

The carboxyl group and the amino group of an amino acid can be considered to be what type of chemical?

Answer 2

They can each be considered to be weak acids.

Question 3

Why are the carboxyl group and the amino group of amino acids considered to be weak acids?

Answer 3

Because they only partially dissociate in water whereas strong acids completely dissociate.

Question 4

What does the carboxyl group dissociate to?

Answer 4

COO-.

Question 5

What does the amino group dissociate to?

Answer 5

NH2.

Question 6

What is the Ka of an acid?

Answer 6

The dissociation constant.

Question 7

What is the Henderson Hasselbalch equation?

Answer 7

pH = pKa + log * conjugate base/acid.

Question 8

What does the pH stand for in the Henderson Hasselbalch equation?

Answer 8

The negative log of the proton concentration.

Question 9

What does the pKa stand for in the Henderson Hasselbalch equation?

Answer 9

The negative log of the Ka.

Question 10

What is the Henderson Hasselbalch equation used to determine?

Answer 10

The pH of a solution, once a strong base or acid has been added to it.

Question 11

The Henderson Hasselbalch equation is particularly useful when creating what kind of solution?

Answer 11

Buffer solutions.

Question 12

What is a buffer solution?

Answer 12

A solution that resists changes in pH when an acid or base is added to that solution.

Question 13

How is a buffer solution made?

Answer 13

By mixing a weak acid with its conjugate base.

HA + A-.

Question 14

The most effective buffer solutions contain what proportion of weak acid to conjugate base?

Answer 14

The best buffer solutions have the same amounts of weak acid and conjugate base.

Question 15

Are all buffer solutions effective at any pH?

Answer 15

No, buffer solutions are only effective at a certain pH.

Question 16

What is the buffering range of a buffer solution?

Answer 16

The pH range at where the buffer is effective.

Question 17

What is the usual buffering range of a buffer solution?

Answer 17

The pKa of the acid + or - 1.

Question 18

What would be the buffering range for an acid with a pKa of 2.8?

Answer 18

The buffering range would be between 1.8 and 3.8.

Question 19

What happens when pH of the solution is equal to the pKa of the acid?

Answer 19

Exactly 1/2 of the molecules are in a dissociated form and exactly 1/2 are undissociated.

Question 20

If HA is the acid and A- is a base that is added to the acidic solution, what will happen?

Answer 20

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+.

Question 21

When is an acid or base at its best as a buffer?

Answer 21

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.

Question 22

How many pKs do the non-polar and the polar uncharged amino acids have?

Answer 22

2 pKs.

Question 23

How many pKs do the acidic and basic amino acids have?

Answer 23

3 pKs.

Question 24

What will the structure of alanine look like at a low pH?

Answer 24

It will be fully protonated.

The amino end will be NH3+.

The carboxyl end will be COOH.

Question 25

The fully protonated form of alanine has what charge?

Answer 25

+1.

Question 26

As you increase the pH of the solution containing the fully protonated form of alanine, what will happen?

Answer 26

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-.

Question 27

Describe the pK1 of alanine?

Answer 27

This is when half of the carboxyl group is in COO- and the other half is in the COOH form.

Question 28

Is alanine a particularly good buffer at pK1?

Answer 28

Yes.

Question 29

As pH increases in a solution with alanine at pK1, what happens?

Answer 29

The carboxyl end completely dissociates to COO-, this is when alanine reaches its isoelectric point (PI).

Question 30

What is the isoelectric point of an amino acid?

Answer 30

When the molecule has a net charge of 0.

Question 31

How do you calculate the PI of an amino acid?

Answer 31

PK1 + PK2 / 2.

Question 32

Are amino acids good buffers when they are at their isoelectric point?

Answer 32

No. They are the worst buffers at their PI.

Question 33

What happens to alanine in its isoelectric form if more base is added to the solution?

Answer 33

The amino end will donate a proton to the media going from NH3+ to NH2.

Question 34

When does alanine reach its pK2?

Answer 34

When exactly half of the amino group is in its NH3+ form and the other half is in NH2 form.

Question 35

Is alanine a good buffer at pK2?

Answer 35

Yes.

Question 36

What happens to alanine in its pK2 form if more base is added to the solution?

Answer 36

The NH3+ will completely dissociate to form NH2.

Question 37

What charge does the completely dissociated form of alanine have?

Answer 37

COO- and NH2 give a charge of -1.

Question 38

How is the titration of an acidic or basic amino acid differ from a non polar or polar uncharged amino acid?

Answer 38

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.

Question 39

How do you calculate the PI for a basic or acidic amino acid?

Answer 39

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.

Question 40

How can water act as a solvent for macromolecules?

Answer 40

By forming hydrogen bonds with them.

Question 41

What is homeostasis?

Answer 41

When the bodys acid and base levels are normal. The body is at physiological pH.

Question 42

What is physiological pH?

Answer 42

7.36 and 7.44. With extreme ranges of 6.8 - 7.8.

Question 43

How do the lungs buffer the acid levels in the body?

Answer 43

They remove CO2, which if left in the blood could form carbonic acid.

Question 44

How do the kidneys buffer the acid levels in the body?

Answer 44

They remove ammonia and H+ which could form ammonium.