6.2.2 - Amino Acids, Amides and Chirality

Question 1

What are amino acids?

Answer 1

The building blocks of biological molecules called peptides and proteins.

Question 2

What are proteins called?

Answer 2

Polypeptides.

Question 3

How many different amino acids are there in the body?

Answer 3

20

Question 4

What are alpha amino acids?

Answer 4

Both the basic amine group (NH2) and the acid carboxyl group are bonded to the same carbon atom.

Question 5

What is the general formula for an amino acid?

Answer 5

RCH(NH2)COOH

Question 6

What kind of carbons do amino acids generally have?

Answer 6

Chiral carbons.

Question 7

What can amino acids act as?

Answer 7

An acid or a base (they are amphoteric).

Question 8

What part of amino acid reacts with bases/alkalis?

Answer 8

The COOH group. The base removes H+ to produce the carboxylate salt, COO-

Question 9

What part of amino acid reacts with acids?

Answer 9

NH2 group. The acid supplies H+ to produce an ammonium salt, NH3+

Question 10

Amino acids with alcohols and what conditions?

Answer 10

Forms an ester with concentrated sulphuric acid catalyst.

Question 11

What is a zwitterion?

Answer 11

Where an internal salt can be formed due to the acidic carboxyl group (COOH) and the basic amine group (NH2) in the amino acid interacting.

Question 12

What happens when a zwitter ion is formed?

Answer 12

A proton is transferred from the acidic carboxyl group to the basic amine group.

Question 13

What is the charge on a zwitterion?

Answer 13

The ion contains a positive and negative charge so has no overall charge.

Question 14

What is the isoelectric point?

Answer 14

The specific pH at which an amino acid exists as a zwitterion.

Question 15

What happens to the zwitterion when H+ ions are added?

Answer 15

Acts as a base and so accepts a proton forming NH3+

Question 16

What happens to the zwitterion when OH- ions are added?

Answer 16

Acts as an acid, donating a proton.

Question 17

What is chirality?

Answer 17

When a carbon has 4 different groups attached to it.

Question 18

What does a molecule containing a chiral carbon have?

Answer 18

No plane of symmetry so has a non-superimposable mirror image. These molecules are called optical isomers (enantiomers)

Question 19

What do optical isomers do?

Answer 19

Rotate plane polarised light by equal amounts in opposite directions.

Question 20

What does a racemic mixture mean?

Answer 20

The mixture contains equal amounts of both optical isomers so does not rotate plane polarised light.

Question 21

Are carbons in the benzene ring chiral?

Answer 21

No.

Question 22

What is an amide?

Answer 22

Contains an acyl group attached to a nitrogen.

Question 23

Primary amide structure?

Answer 23

The nitrogen atom has 2 hydrogens and they have the general formula RCONH2

Question 24

Secondary amide structure?

Answer 24

The nitrogen atom has 1 hydrogen and they have the general formula RCONHR’

Question 25

How are primary amides produced?

Answer 25

Reaction of acyl chloride and ammonia.

Question 26

RCOCl + NH3 ->

Answer 26

RCONH2 + HCl

Question 27

RCOCl + 2NH3 ->

Answer 27

RCONH2 + NH4Cl

Question 28

How are secondary amides formed?

Answer 28

The reaction of an acyl chloride with a primary amine.