what are heterocyclic amino acids? i mean understand how amino acids are cyclic in the first place.

plz explain this .. and tell me do i need to know it for NEET?

then what are non non protein amino acids?

  • Amino acids are of three types regarding special structure.

They are

  1. Sulphur containing Amino acids
  2. Alcoholic Amino acids
  3.  Heterocyclic amino acids.


Of which the heterocyclic amino acids have Nitrogen within the ring structure. e.g., Histidine, Proline. The prefix hetero- means “other.” The nitrogen atom is an “other” atom—an atom other than carbon—in the ring itself. 


  • Proline, the only proteinogenic amino acid, is the odd one out among the amino acids. Proline has four carbons; with the alpha amino group bonded not only to the alpha carbon but also to the last side chain carbon. It makes proline as imino acid and the carbon-carbon bonds of proline do not rotate in solution. The cyclic side chain means that proline is conformationally rigid. Other amino acids are more flexible in solution.


This answer is based on my understanding of the question. I could not interpret your query. Please be a little specific so that i could provide you meaningful help. We look forward to hear from you again! 


  • CORE SYLLABUS for National Eligibility-Cum-Entrance Test (NEET) has biomolecules. So, Knowing about amino acids would be an added advantage for you.
  • Amino acids are the building blocks of protein. Around 20 amino acids are normal components of cell protein. But many amino acids found in cells do not form proteins. These are called non protein amino acids which are not encoded in the genetic code. Some examples: Ornithine, Citrulline

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