6.2.2- Amino Acids, Amides and Chirality

Question 1

What are the two functional groups of amino acids?

Answer 1

NH2 and COOH (amino and carboxylic acid)

Question 2

Are alpha-amino acids chiral? Why?

Answer 2

Yes, one carbon has 4 different substituents. Except glycine, where R=H

Question 3

Define a zwitterion

Answer 3

Ions which have both a permanent positive and negative charge, but are neutral overall.

Question 4

How do zwitterions occur in amino acids?

Answer 4

COOH is deprotonated -> COO-
NH2 is protonated -> NH3+

Question 5

What happens to amino acids in acidic conditions?

Answer 5

Gains a proton on NH2 group

Question 6

What happens to amino acids in alkaline conditions?

Answer 6

Loses a proton from COOH group

Question 7

What is the peptide linkage?

Answer 7

-CONH-

Question 8

What property must a carbon atom have for the molecule to display optical isomerism about that carbon atom?

Answer 8

4 different substituents attached to one carbon atom

Question 9

What are similarities and differences between two optical isomers?

Answer 9

• Same atoms and bonds, but they are non-superimposable mirror images of one another. Not identical in chemical properties necessarily.
• Differ in the way they rotate plane polarised light- rotate plane of polarisation by the same angle but in different directions.

Question 10

What word is used to describe optically active molecules?

Answer 10

Chiral

Question 11

Give 2 examples of chiral molecules

Answer 11

All alpha amino acids, except glycine
Lactic acid/ 2-hydroxypropanoic acid