CBS - Amino Acids

Question 1

Describe what an amino acid is.

Answer 1

It is a molecule with an amino group and carboxylic group attached to the same carbon (known as the α- carbon).

Amino acids have different R-groups attached to the α- carbon. The R-group defines the physical properties and function of the amino acid.

The amino and carboxyl group are ionised at physiological pH.

There are 20 universal DNA-encoded amino acids that exist.

Question 2

Define essential amino acids (in adults).

Answer 2

They are amino acids that cannot be synthesised de novo by humans, as we lack the necessary enzymes.

Question 3

List the essential amino acids.

Answer 3

• threonine
• methionine
• lysine
• valine
• leucine
• isoleucine
• histidine
• phenylalanine
• tryptophan

Question 4

List the two negatively charged amino acids.

Answer 4

Aspartic acid (Asp)

Glutamic acid (Glu)

Question 5

List the three positively charged amino acids.

Answer 5

Arginine (Arg)

Lysine (Lys)

Histidine (His) (sometimes)

Question 6

Why is histidine important?

Answer 6

It has a complex nitrogen carbon ring structure, and because of the pKa of this amino acid, it can be positively charged or not.

Hence, it plays an important part in buffering haemoglobin but also other proteins.

Question 7

List the uncharged, polar/hydrophilic amino acids, with an amide R group.

Answer 7

Asparagine (Asn)

Glutamine (Gln)

Question 8

List the uncharged polar/hydrophilic amino acids, with a hydroxyl R group.

Answer 8

Serine (Ser)

Threonine (Thr)

Question 9

List the uncharged polar/hydrophilic amino acid, with a benzene ring R group.

Answer 9

Tyrosine (Tyr)

Question 10

List the nonpolar amino acid, with no R group.

Answer 10

Glycine (Gly)

Question 11

List the nonpolar/hydrophobic amino acids, with an aliphatic R group.

Answer 11

Alanine (Ala)

Valine (Val)

Leucine (Leu)

Isoleucine (Ile)

Question 12

List the nonpolar/hydrophobic amino acid, with a ring structure (including an α-amino R group).

Answer 12

Proline (Pro)

Question 13

List the nonpolar/hydrophobic amino acid, with a benzene ring R group.

Answer 13

Phenylalanine (Phe)

Question 14

List the nonpolar/hydrophobic amino acid, with a sulphur-containing R group.

Answer 14

Methionine (Met)

Question 15

List the nonpolar/hydrophobic amino acid, with a ring structure R group.

Answer 15

Tryptophan (Trp)

Question 16

List the nonpolar/hydrophobic amino acid, with a ring structure R group.

Answer 16

Cysteine (Cys)

Question 17

List some examples of clinical considerations of amino acid changes.

Answer 17

PHENYLKETONURIA (PKU):
This results in a defective phenylalanine hydroxylase (which converts phe→tyr)

The reduced tyrosine results in reduced dopamine production, as well as reduced melanin production.

There is also an increase in other phenylalanine by-products e.g. phenylacetate

ALBINISM (many forms):
This comes as a reults of a defective tyrosinase (which converts tyr → melanin)