Amino Acids

Question 1

What are amino acids and how do they build polypeptide chains?

Answer 1

Amino acids are monomers or proteins. Amino acids are joined by peptide bonds during condensation reactions to form polypeptide chains.

Question 2

What is common structure of amino acids?

Answer 2

• Carboxylic acid -COOH
• Amino group - NH2
• H atom
• R group (unique for every amino acid so determines identity)

Question 3

Polypeptide chain has directionality. What does this mean?

Answer 3

Two ends of chain are chemically distinct. N-terminus (amino end) has a free amino group. C-terminus (carboxyl end) has a free carboxyl group.

Question 4

What determines chemical behaviour of amino acid?

Answer 4

The R group

Question 5

Lysine (at physiological pH)

Answer 5

Electrically charged: side chain is positively charged. Considered basic amino acid

Question 6

Acidic Amino Acids: side chains are negatively charged

Answer 6

Aspartic acid (Asp)
Glutamic acid (Glu)

Question 7

Basic Amino Acids: side chains are positively charged

Answer 7

Lysine (Lys)
Arginine (Arg)
Histidine (His)

Question 8

Non-Polar (Hydrophobic) Amino Acids

Answer 8

Glycine (Gly) 
Alanine (Ala)
Valine (Val) 
Leucine (Leu) 
Isoleucine (Ile)
Methionine (Met)
Tryptophan (Trp) 
Phenylalanine (Phe)
Proline (Pro)

Question 9

Polar (Hydrophilic) Amino Acids

Answer 9

Serine (Ser)
Threonine (The)
Cysteine (Lys)
Tyrosine (Tyr)
Asparagine (Asn)
Glutamine (Gln)

Question 10

Glycine at physiological pH?

Answer 10

Non-polar (hydrophobic)

Question 11

Histidine at physiological pH?

Answer 11

Side chain is positively charged: basic amino acid.

ALTHOUGH, at pH 7 side chain is mainly uncharged

Question 12

Arginine at physiological pH?

Answer 12

Side chain is positively charged: basic amino acid

Question 13

Which is the only amino acid that isn’t chiral / doesn’t posses optical activity?

Answer 13

Glycine

Question 14

What do optical isomers do?

Answer 14

Rotate plane-polarised light in opposite directions

Question 15

What is physiological pH?

Answer 15

7.2-7.4

Question 16

At physiological pH, what is the amino group and carboxyl group typically like?

Answer 16

Amino group typically protonated (has positive charge)

Carboxyl group typically deprotonated (has negative charge)

Question 17

What is pKa?

Answer 17

The pH at which a group is 50% ionised

Question 18

What is the pKa for carboxylic acid groups?

Answer 18

Roughly 1.8 – 2.5; almost always negatively charged

Question 19

What is the pKa for amino groups?

Answer 19

Roughly 9-10; almost always positively charged

Question 20

What is the pKa for histidine?

Answer 20

Roughly 6.0

Question 21

If a pH is below pKa, what is seen?

Answer 21

Group will have H attached