Structure of RNA

Structure of RNA


  • RNA are unbranched polymeric molecules composed of nucleoside monophosphates joined together by phosphodiester bonds.
  • They are considerably smaller than DNA. does  not  possess  thymine  except  in rare  cases.
  • single-stranded and does not exhibit the equivalence of adenine with uracil and cytosine with guanine.

“S” is the Svedberg unit, which is related to the molecular weight and shape of the compound.

Messenser RNA (mRNA)

  • It carries the information (message) from the nucleus to to ribosome.
  • Synthesized  in  the  nucleus as’heterogenous  RNA (hn  RNA).
  • Its nucleotide  sequence is  complementary i.e adenine for thyamine, guanine for Cytosine, uracil for adenine (as RNA does not contain thymine) and cytosine for guanine.
  • 2-5% of total cellular RNA
  • 5′ end capped by 7 Methylguanosine triphosphate
  • 3′ end nongenetically encoded by polymer of 20-250 adenylate residues.
  • m RNA carries genetic information in the form of codons FOR SPECIFIC AMINO ACIDS.

Transfer RNA (tRNAs) 

  • The smallest (4S) of the three major types of RNA molecules.
  • tRNAs make up about 15% of the total RNA in the cell.
  • contain a high percentage of unusual bases (for example, dihydro uracil).
  • extensive intrachain base-pairing that leads to characteristic secondary  and tertiary structure.
  • RNA  which  transfer  amino  acid from  the  cytoplasm to  the  ribosomal  protein  synthesizing machinery.
  • Clover  leaf  shape in  the  secondary  structure, L shaped  tertiary  structure.
  • Cytoplasmic  translation  system  possess 31tRNA species.
  • Mitochondrial  translation  system  possess  22  tRNA species.

t-RNA  molecule  get  folded  into  a  structure  that  appears  like  a  clover  leaf.  There are  four  arms.

1)  Acceptor arm: 

  • Base  paired  stem that terminates  in  the sequence  CCA  at  the  3’ end,
  • Attachment site for  amino  acids.
  • CCA  tail is  added  during  post-transcriptional  modification.

2) D arm:  It contains  the  base  dihydrouridine.

3) Anticodon  arm:  It  contains  anticodon.

3.1) TΨC arm: It contains  both  ribothymidine  (T)  and pseudouridine  (Ψ).

Ribosomal  RNA (r  RNA)

  • rRNA  is  present  in ribosomes.
  • made up of two  subunits  40  ‘S’  and  60  ‘S ¥(eukaryotes).
  • The  40 S subunit  is  made up  of 18  S rRNA  and  about  30 different  polypeptides.
  • The  60  S subunit  is  made  up  of three types  of rRNA  :  55  rRNA,  5.8  S rRNA and 28S rRNA.
  • The Ribosomal RNAs (28  S+I8 S) represent  roughly  70%o  of  total  cellular  RNA.
  • many  ribosomes  can be  associated  with  mRNA  molecule  to  form  an assembly called  the  polysome.
  • Some rRNAs  also  have  ribozymal  activity.
  • r-RNA  is  sytrthesized  in  the  nucleolus
Don’t Forget to Solve all the previous Year Question asked on Structure of RNA

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