Test: Chemistry and Metabolism of Amino Acids- 1 - NEET PG MCQ

• The stop codon UGA encodes for Selenocysteine.
• The stop codon UAG encodes for Pyrrolysine.

Amino acids are categorised based on nutritional needs into the following groups:

• Essential: These amino acids cannot be produced by the body and must be obtained through the diet.
• Semiessential: These are necessary in the diets of growing children but are not critical for adults.
• Nonessential: These amino acids can be synthesised by the body, meaning they are not necessary in the diet.

• Polar amino acids have side chains that can form hydrogen bonds with water (hydrophilic).

• Serine – polar, contains a hydroxyl (-OH) group.

• Tyrosine – polar, contains a phenolic (-OH) group.

• Lysine – polar, basic amino acid with an amino group (-NH3⁺).

• Tryptophan – mostly nonpolar, slightly polar due to nitrogen in indole ring but generally considered nonpolar.

• Valine – nonpolar, hydrophobic side chain.

So the polar amino acids among the given options are Serine, Tyrosine, and Lysine.

1. Alanine – Nonpolar (hydrophobic side chain: -CH3).

2. Tryptophan – Slightly polar (aromatic ring with nitrogen, not fully nonpolar).

3. Isoleucine – Nonpolar (hydrophobic branched side chain).

4. Lysine – Polar, basic (positively charged at physiological pH).

5. Tyrosine – Polar (hydroxyl group in side chain).

Correct answer: Alanine, Isoleucine

So the correct nonpolar amino acids are:
a) Alanine and c) Isoleucine.

• The primary amino acids include Histidine, Arginine, and Lysine.
• The acidic amino acids consist of Aspartic Acid (Aspartate) and Glutamic Acid (Glutamate).

The distinctive group in phenylalanine is the benzene ring.

In tyrosine, the unique group is the phenol ring.

The enzyme responsible for the hydroxylation of phenylalanine to tyrosine is known as phenylalanine hydroxylase.

Essential amino acids include Methionine, Threonine, Tryptophan, Valine, Isoleucine, Leucine, Phenylalanine, Lysine (remembered with the mnemonic MeTT VIL PhLy), and Histidine. The semi-essential amino acid is Arginine.

• Histidine (featuring an Imidazole ring)
• Phenylalanine (containing a Benzene ring)
• Tyrosine (which has a Phenol ring)
• Tryptophan (possessing an Indole ring)

Branched chain amino acids, which consist solely of essential amino acids, include:

• Leucine
• Isoleucine
• Valine

The group of amino acids that solely comprises non-essential amino acids includes:

• Acidic amino acids
• Amide group containing amino acids
• Imino acids
• Simple amino acids

• Glutamine and Asparagine are amino acids that contain an amide group.
• Aspartate and Glutamate are classified as acidic amino acids.

Semiessential amino acid, arginine, plays a vital role in various bodily functions.

• It is crucial for protein synthesis.
• Arginine aids in the production of nitric oxide, which is important for blood flow.
• This amino acid supports the immune system by promoting the activity of T-cells.
• Additionally, it contributes to wound healing and tissue repair.

While the body can produce arginine, it may be necessary to obtain it from dietary sources, especially during periods of stress or illness.

Derived amino acids do not necessitate Aminoacyl tRNA. Of the listed options, Hydroxyproline is classified as a derived amino acid.

• Tryptophan
• Phenylalanine
• Tyrosine

Protein kinases phosphorylate proteins by facilitating the transfer of the terminal phosphoryl group from ATP to the hydroxyl groups of seryl, threonyl, or tyrosyl residues. This process results in the formation of O-phosphoseryl, O-phosphothreonyl, or O-phosphotyrosyl residues, respectively.

• The most frequent sites of phosphorylation are Serine and Threonine.
• Tyrosine follows as the next common site.

• Factor II (Prothrombin)
• Factor VII (Proconvertin or Serum Prothrombin Conversion Accelerator, SPCA)
• Factor IX (Antihemophilic factor or Christmas factor)
• Factor X (Stuart Prower factor)
• Protein C
• Protein S
• Osteocalcin
• Nephrocalcin

Glycine is the sole amino acid that does not exhibit optical activity.

Amino acids primarily occur in L forms, while carbohydrates are generally found in D forms.

The only amino acid that is optically inactive is Glycine.