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Biochem Take 2. > Acid Base Chemistry of Amino Acids. > Flashcards

Acid Base Chemistry of Amino Acids. Flashcards

1
Q

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

A

The amino and carboxyl groups.

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2
Q

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

A

They can each be considered to be weak acids.

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3
Q

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

A

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

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4
Q

What does the carboxyl group dissociate to?

A

COO-.

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5
Q

What does the amino group dissociate to?

A

NH2.

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6
Q

What is the Ka of an acid?

A

The dissociation constant.

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7
Q

What is the Henderson Hasselbalch equation?

A

pH = pKa + log * conjugate base/acid.

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8
Q

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

A

The negative log of the proton concentration.

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9
Q

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

A

The negative log of the Ka.

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10
Q

What is the Henderson Hasselbalch equation used to determine?

A

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

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11
Q

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

A

Buffer solutions.

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12
Q

What is a buffer solution?

A

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

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13
Q

How is a buffer solution made?

A

By mixing a weak acid with its conjugate base.

HA + A-.

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14
Q

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

A

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

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15
Q

Are all buffer solutions effective at any pH?

A

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

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16
Q

What is the buffering range of a buffer solution?

A

The pH range at where the buffer is effective.

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17
Q

What is the usual buffering range of a buffer solution?

A

The pKa of the acid + or - 1.

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18
Q

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

A

The buffering range would be between 1.8 and 3.8.

19
Q

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

A

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

20
Q

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

A

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+.

21
Q

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

A

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.

22
Q

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

A

2 pKs.

23
Q

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

A

3 pKs.

24
Q

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

A

It will be fully protonated.

The amino end will be NH3+.

The carboxyl end will be COOH.

25
Q

The fully protonated form of alanine has what charge?

A

+1.

26
Q

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

A

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-.

27
Q

Describe the pK1 of alanine?

A

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

28
Q

Is alanine a particularly good buffer at pK1?

A

Yes.

29
Q

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

A

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

30
Q

What is the isoelectric point of an amino acid?

A

When the molecule has a net charge of 0.

31
Q

How do you calculate the PI of an amino acid?

A

PK1 + PK2 / 2.

32
Q

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

A

No. They are the worst buffers at their PI.

33
Q

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

A

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

34
Q

When does alanine reach its pK2?

A

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

35
Q

Is alanine a good buffer at pK2?

A

Yes.

36
Q

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

A

The NH3+ will completely dissociate to form NH2.

37
Q

What charge does the completely dissociated form of alanine have?

A

COO- and NH2 give a charge of -1.

38
Q

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

A

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.

39
Q

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

A

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.

40
Q

How can water act as a solvent for macromolecules?

A

By forming hydrogen bonds with them.

41
Q

What is homeostasis?

A

When the bodys acid and base levels are normal.

The body is at physiological pH.

42
Q

What is physiological pH?

A

7.36 and 7.44.

With extreme ranges of 6.8 - 7.8.

43
Q

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

A

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

44
Q

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

A

They remove ammonia and H+ which could form ammonium.

Biochem Take 2. (24 decks)

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