IGCSE Biology Paper-1: Specimen Questions with Answers 192 - 192 of 208

Question 192




Which simple molecules are the basic units of protein?


Choice (4)
a.Amino acids
c.Fatty acids




  • Amino acids: Amino acids are normal components of cell proteins (called amino acid). They are 20 in number specified in genetic code and universal in viruses, prokaryotes, and eukaryotes. Otherwise amino acids may be termed rare amino acids, which take part in protein synthesis e. g. hydroxyproline and non- protein amino acids do not take part in protein synthesis e. g. Ornithine, citrulline, gama-aminobutyric acid (GABA) a neurotransmitter, etc.
  • Structure and Composition: Amino acids are basic units of protein and made up of C, H, O, N and sometimes S. Amino acids are organic acids with a carboxyl group (–COOH) and one amino group on the α -carbon atom. Carboxyl group attributes acidic properties and amino group gives basic ones. In solution, they serve as buffers and help to maintain pH. General formula is .
  • Amino acids are amphoteric or bipolar ions or Zweitter ions. Amino acids link with each other by peptide bond and long chains are called polypeptide chains.
Long Chains are Called Polypeptide

Long Chains Are Called Polypeptide

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