Amino Acid Properties

Question 1

Which amino acid has the highest R group pKa?

Answer 1

Arginine, pKa of 12.5

Question 2

Which group on an amino acid has the lowest pKa?

Answer 2

Alpha Carboxyl group

Question 3

What is the pKa of the alpha amino group?

Answer 3

8

Question 4

Proteins exclusively contain: L or D amino acid isomers

Answer 4

L-amino acids are only found in proteins, L and D reflect R and COO- groups

Question 5

Where would a carbon labelled C-1 be on an amino acid?

Answer 5

This would be the carboxyl carbon, not same place as alpha-carbon which is chiral

Question 6

An ion which contain both positive and negative charges ic called…

Answer 6

a zwitterion

Question 7

A compound with a low pKa would be an acid or a base?

Answer 7

Acid (stronger if lower pKa)

Question 8

What is the Henderson-Hasselbach equation?

Answer 8

pH = pKa+ log([A-]/[HA])

Question 9

If the pH of a weak acid solution is greater than its pKa, what would the relative concentrations of A- and H+ be?

Answer 9

Conc. A- is greater than conc. HA

Question 10

What is phosphorylation (in relation to proteins)?

Answer 10

The addition of a phosphate group to a polar, neutral amino acid in place of a hydroxyl group (affect S, T, Y -> MAPK)

Question 11

What 3 amino acids may be phosphorylated?

Answer 11

Serine (S), Tyrosine (Y) and Threonine (T)

Question 12

What is the use of phosphorylation?

Answer 12

Modulating protein function, cellular signalling, protein kinases

Question 13

What disease is caused by a mutation in protein kinases?

Answer 13

Cancer (Protein kinases phosphorylate proteins)

Question 14

What are the 6 Amino acids which are hydrophobic, with a non polar R group?

Answer 14

Glycine (G), Alanine (A), Valine (V), Leucine (L), Isoleucine (I) and Methionine (M)

Question 15

Which amino acid is the most hydrophobic?

Answer 15

Methionine, due to methyl-thioether (methyl group bound to Sulphur)

Question 16

What is the ring structure in proline known as?

Answer 16

Pyrrolidine Ring

Question 17

Which amino acid from does proline favour?

Answer 17

Trans form (most Amino acids favour the cis form)

Question 18

Which amino acid are aromatic?

Answer 18

Phenylalanine (F), Tryptophan (W), Histidine (H), Tyrosine (Y) - but Histidine does not absorb light at 280nm like others

Question 19

Which amino acids contain Hydroxy groups?

Answer 19

Serine (S), Threonine (T), Tyrosine (Y) —> can be phosphorylated

Question 20

What amino acid has a pKa very similar to physiological pH and as such is uncharged and can act as acid/base?

Answer 20

Histidine (H), ability to conduct acid/base chemistry makes it useful in enzymes such as carbonic anhydrase

Question 21

What enzyme forms 4 disulphide bonds and is used by the body to defend against infection?

Answer 21

Lysozyme(s)

Question 22

What amino acids are positively charged?

Answer 22

Lysine (K), Arginine (R) and sometimes Histidine (H) - contribute to basicity

Question 23

What is the major driving force behind protein folding?

Answer 23

Hydrophobic character of residues

Question 24

What mentioned enzyme is Histidine (H) present in?

Answer 24

Carbonic Anhydrase

Question 25

What form is usually favoured by Amino acids in a peptide?

Answer 25

Cis form, reduces steric crowding

Question 26

Between which atoms does a peptide bond form?

Answer 26

Partial double bond forms between nitrogen of amide and carbon of carbonyl

Question 27

Would the N-terminal amide be at the left or right of a linear peptide?

Answer 27

Left hand side (start)