Polymers of Life 4: Amino Acids

Question 1

What is the general structure of an amino acid

Answer 1

H
            I
H2N - C - COOH
            I
           R

Question 2

What 2 functional groups are contained in amino acids

Answer 2

1. Amine, NH2

2. Carboxylic acid , COOH

Question 3

What do amines act as and why

Answer 3

Bases due to lone pair

Question 4

What can carboxylic acids act as and why

Answer 4

Acids due to H+ ion which then can lose

Question 5

What is the rule for naming amino acids

Answer 5

COOH group acts as 1st carbon

Question 6

Name this amino acid ( aka glycine)

           H
            I
H2N - C - COOH
            I
           H

Answer 6

2-aminoethanoic acid

Question 7

Name this amino acid ( aka valine )

           H
            I
H2N - C - COOH
            I
           CH - CH3
            I
           CH3

Answer 7

2 - amino-3- methyl butanoic acid

Question 8

Name this amino acid ( aka serine )

           H
            I
H2N - C - COOH
            I
           CH2OH

Answer 8

2-amino-3-hydroxypropanoic acid

Question 9

Name this amino acid ( aka aspartic acid)

           H
            I
H2N - C - COOH
            I
           CH2 COOH

Answer 9

2-aminobutan-1,4-dioic acid

Question 10

What is special about amino acids ( in terms of optical isomers )

Answer 10

• they are chiral ( except glycine where R = H )

- only 1 enantiomer occurs usually naturally have to synthesis in a lab if want mirror image

Question 11

What happens to amines at neutral pH in water

Answer 11

• amine +ve charged
• carboxylic acid -ve charged

= zwitterion= positive & negative charges are present on the same molecule

Question 12

Definition of zwitterion

Answer 12

positive & negative charges are present on the same molecule

Question 13

What happens to amines at low pH ( 1-7 = acidic )

Answer 13

• base i.e amine group gets protonated

Question 14

What happens to amines at high pH ( 7-14 = alkali )

Answer 14

• Carboxylic acids = negatively charged

- starts to act as an acid

Question 15

Reactions of amino acids in terms of amine group

Answer 15

• protonated by acids
• acylation with acyl chloride / acid anhydride
• nucleophilic substitution with halogenoalkanes

Question 16

Reactions of amino acids in terms of carboxylic acid group

Answer 16

• deprotonated by bases

- esterification with alcohols ( with acid catalyst )

Question 17

What does joining amino acids form and what kind of reaction is this

Answer 17

• Polypeptides and proteins

- Condensation polymerisation

Question 18

What do peptides contain

Answer 18

Amide linkage = COCH

Question 19

How are polypeptides brown down and into what products

Answer 19

• Hydrolysis reaction

- amino acid & proteins

Question 20

Definition of hydrolysis reaction

Answer 20

• requires acid / enzyme

- reaction with water in which O-H bond breaks

Question 21

How do you test for different amino acids

Answer 21

TLC - thin layer chromatography

Question 22

How do you identify acid in a TLC

Answer 22

Spray plate with ninhydrin

= sticks to amino acids on the plate and shows them up in different colours

= identification of spots without UV light becomes possible

Question 23

What is the rule for Rf values

Answer 23

Should always be < 1

Question 24

How would you describe any amino acid with a benzene ring

Answer 24

Aromatic ( everything else is aliphatic )