lecture 4 - amino acids & peptides

Question 1

What is the basic structure of an amino acid?

Answer 1

Central alpha carbon, R side chain, amino group, carboxylic group

Question 2

Are amino acids in nature L or D stereoisomers?

Answer 2

Almost always L

Question 3

Which amino acid does not have a chiral carbon, and is therefore not a stereoisomer?

Answer 3

Glycine

Question 4

As the pH of a solution increases, are amino acids protonated or deprotonated?

Answer 4

deprotonated

Question 5

What are the 3 key classifications of amino acids?

Answer 5

Non-polar, polar (uncharged), polar (charged)

Question 6

What are the 2 amino acids that have acidic side chains?

Answer 6

Aspartame, glutamate

Question 7

What are the 3 amino acids that have basic side chains?

Answer 7

Lysine, arginine, histidine

Question 8

How would an amino acid mutation in a protein be described using single letter codes?

Answer 8

3 letter code for mutation - 1st letter=original aa, 2nd letter=location of mutant on protein chain, 3rd letter=new residue

Question 9

What reaction type is involved in the formation of a disulphide bond?

Answer 9

Oxidation reaction

Question 10

What is the double bond character of the peptide bond?

Answer 10

40% double bond character

Question 11

Is the peptide bond planar or non-planar?

Answer 11

Planar

Question 12

What is the value of the rotational barrier of the peptide bond?

Answer 12

80KJ/mol

Question 13

What is the ‘rotational barrier’ of a bond?

Answer 13

The difference in energy between the most stable and least stable configurations of rotation around a bond.

Question 14

Are peptide bonds usually cis or trans?

Answer 14

Trans

Question 15

Why do peptide bonds have dipoles?

Answer 15

The double bond resonance form produces a dipole

Question 16

What is the name for an amino acid when it is in a polypeptide chain?

Answer 16

An amino acid residue

Question 17

Are amino acids typically charged or uncharged in solution?

Answer 17

Usually exist as zwitterions in neutral solution so have a net neutral charge, but the side amino and carboxyl groups are equally and oppositely charged.

Question 18

What is the nature of an amino acid at its pI?

Answer 18

Has no net charge

Question 19

What is the pI of an amino acid?

Answer 19

The isoelectric point - the pH at which an amino acid has no net charge

Question 20

Which amino acid is involved in disulfide bridge formation?

Answer 20

Cysteine

Question 21

What is phosphorylation, in terms of amino acid modification?

Answer 21

The covalent addition of a phosphate group to a residue

Question 22

What is hydroxylation, in terms of amino acid modification?

Answer 22

The addition of a hydroxyl (OH) group to an amino acid

Question 23

What is carboxylation, in terms of amino acid modification?

Answer 23

The addition of a carboxylate group to an amino acid residue

Question 24

What is metal binding, in terms of amino acid modification?

Answer 24

The binding of a metal ion to a peptide

Question 25

What is iodination, in terms of amino acid modification?

Answer 25

The addition of an iodine atom to an amino acid residue/protein

Question 26

What is glycosylation, in terms of amino acid modification?

Answer 26

The addition of a sugar/carbohydrate molecule to an amino acid in a protein chain.