Effect of pH on amino acids

Question 1

When something is protonated does it gain or lose an electron? What are two examples?

Answer 1

When protonated an electron is gained
Below isoelectric point
Examples are COO and NH2

Question 2

When something is deprotonated does it gain or lose an electron? What are two examples?

Answer 2

When deprotonated an electron is lost
Above isoelectric point
Examples are COOH and NH3+

Question 3

What does pKa indicate?

Answer 3

Acid strength

Question 4

What is meant by isoelectric point?

Answer 4

The point at which the amino acid has a neutral charge

Question 5

How is the pi worked out?

Answer 5

Identify the neutral charge point, between the Carboxyl group and the amine group (will be a + on the left and +/- on the right)
Take the 2 pKas from either side and divide them by 2

Question 6

What is the role of a pH buffer?

Answer 6

To resist pH change

Question 7

What is the buffering range?

Answer 7

pKa +/- 1 pH unit

Question 8

What is an example of a biological buffering system?

Answer 8

Bicarbonate

• transports CO2 in the blood, bound to haemoglobin and in the bicarbonate form
• CO2 is exported from cells and converted to carbonic acid which disassociates slowly to carbonate
• In RBCs carbonic anhydrase is used to catalyse the conversion of carbonic acid to carbonate

Question 9

Does an acidic amino acid have a pKa above or below 7?

Answer 9

Below

Question 10

Does an basic amino acid have a pKa above or below 7?

Answer 10

Above

Question 11

What is being described when the term ‘free amino acid’ is used?

Answer 11

Single amino acids- not linked in a chain