6.2.2: Amino acids and chirality

Question 1

Formula of an 𝜶 amino acid

Answer 1

-R
H₂N - C – C =O
-H. –OH

Question 2

What does the ‘𝜶’ prefix indicate?

Answer 2

That the amine group and carboxylic acid group are both attached to the same carbon.

Question 3

Properties of different groups in amino acid

Answer 3

• Amine group = basic, can accept a proton

* Carboxylic group = acidic, can donate a proton

Question 4

How are amino acids capable of acting as buffers?

Answer 4

• They contain weakly acidic and basic groups (so small additions of H⁺ and ⁻OH can be ‘mopped up’
• In this way, small fluctuations of pH can be avoided

Question 5

What is a zwitterion?

Answer 5

The internal salt formed when the carboxylic acid group donates a proton that is picked up by the N.

Question 6

What is the overall charge on a zwitterion?

Answer 6

• 0

* The negative on the O of the carboxylic acid group cancels out the positive on the N of the amino group.

Question 7

What is the isoelectric point?

Answer 7

The pH at which the zwitterion form of the amino acid exists in aqueous solution.

Question 8

What does the isoelectric point depend on?

Answer 8

The R group of the amino acid.

Question 9

At pH below (more acidic than) the isoelectric point…

Answer 9

• The COO⁻ will donate its H⁺ to the amino group
• The COO⁻ will become protonated with an H⁺ from the environment
• The amino acid will exist as a positively charged ion.

Question 10

At pH above (more alkaline than) the isoelectric point…

Answer 10

• OH⁻ ions remove the extra H⁺ from the amino group (the NH₂ group will not be protonated)
• The amino acid will exist as a negatively charged species

Question 11

What is optical isomerism?

Answer 11

type of stereoisomerism in which the mirrors images of the molecules are not superimposable.

Question 12

What is a chiral centre?

Answer 12

carbon atom which has four different groups bonded to it.