Amino acids with the aliphatic ‘R’ group are

The correct option is Glycine, alanine, leucine.

Amino acids are categorized based on the chemical properties of their side chains (R groups). An aliphatic R group consists of hydrocarbon chains that are non-aromatic (meaning they do not contain a benzene ring) and are hydrophobic. These side chains are saturated hydrocarbons consisting only of carbon and hydrogen atoms.

Let's break down the structure of the amino acids in the correct option:
1. Glycine: The simplest amino acid, where the R group is a single hydrogen atom (-H). It is considered aliphatic due to its simple hydrocarbon-like nature.
2. Alanine: Has a methyl group (-CH₃) as its R group, which is a simple aliphatic hydrocarbon.
3. Leucine: Has a branched-chain hydrocarbon R group (-CH₂-CH(CH₃)₂), which is also aliphatic.

Why the other options are incorrect:
- Serine, threonine, cysteine: These contain polar or reactive groups (hydroxyl groups in serine and threonine, and a thiol group in cysteine), not simple hydrocarbons.
- Lysine, arginine, histidine: These have basic (positively charged) side chains.
- Phenylalanine, tyrosine and tryptophan: These contain aromatic rings (benzene or indole rings) and are classified as aromatic amino acids rather than aliphatic.