Steps Of Protein Synthesis (Translation)

STEPS OF PROTEIN SYNTHESIS (Translation)


TRANSLATION 

  • Translation is the process in which the genetic information stored in DNA is passed on to mRNA where it is translated into proteins.
  • Translation occurs in ribosomes.
  • mRNA is translated from its 5’ end to its 3’- end (51 à 31 )
  • 4 letter language information from nucleic acids to 20 letter language proteins.

STEPS OF PROTEIN SYNTHESIS-

  1. Activation of Amino acid
  2. Initiation
  3. Elongation
  4. Termination

1. Activation of amino acid (charging of tRNA)

  • Activation of amino acids takes place cytosol.
  • Each of the 20 amino acids covalently attached to the respective tRNA, by the ATP as two high energy phosphate bond catalyzed by aminoacyl tRNA synthase (AAS) so called as charging tRNA.
  • AAS is identified by DHU arm and is considered as proofreading mechanism of translation.
  • Aminoacyl tRNA synthase – are specific for particular amino acids and tRNA.
  • They are responsible for high fidelity of translation of genetic message.
  • Implements genetic code by acting as molecular dictionaries.
  • 2 ATPs are required for this reaction.

2.  Initiation- is a multi process stage.

  • It is facilitated by accessory proteins called Initiation factors (IF) and for eukaryotic initiation factor (eIF).

a) Ribosomal dissociation

  • Two initiation factors(eIF3 & eIF-1A) binds to 40S subunit of eukaryotic ribosome (80S).
  • 80S ribosomes disassociates into 40S and 60S subunits.

b) Formation of 43S preinitiation complex

  • A ternary complex containing met- tRNA1 and eIF-2(controlling factor in eukaryotes) bound to GTP attaches to 40S subunit to form 43S preinitiation complex.
  •  AUG serves as initiation codon for protein synthesis and codes for methionine

c)Formation of 48S Initiation complex-

  • The binding of mRNA to 43S preinitiation complex results in the formation 48S initiation complex is facilitated by 7- methyguanylate cap at 51 –end of mRNA.
  • In Eukaryotes, Kozak consensus sequence surrounds AUG and determines the initiating codon of mRNA.
  • In Prokaryotes, a sequence of nucleotide bases on mRNA called as Shine- Dalgarno sequence (SD sequence). It is located -6 to -10bp from AUG codon. (purine rich)

d) Formation of 80S initiation complex-

  • 48S initiation complex + 60S subunit = 80S initiation complex
  • 3 sites on 80S Ribosome- A site, P site, E site.

3. Elongation-

  • Catalyzed by proteins called as elongation fators.
  • Has 4 steps-

a) Binding of aminoacyl tRNA to the A-site-

  • Elongation factor EF-1 helps in binding of tRNA.

b) Peptide bond formation-

  • The methionine of tRNA of P- site is transferred to the new amino acid on tRNA of A-site to form peptide bond catalyzed by peptidyl transferase (a ribozyme).

c) Translocation-

  • It requires elongation factor eEF2 (translocase) and hydrolysis of GTP.

4. Termination-

  • Stop codon is in the A site now.
  • In eukaryotes, one single releasing factor, eRF.
  • In prokaryotes, 3 releasing factors- RF- 1, RF-2, RF-3.

Exam Important

  1. Translation occurs in ribosomes.
  2. mRNA is translated from its 5’ end to its 3’- end (51 à 31 )
  3. AAS is identified by DHU arm and is considered as proofreading mechanism of translation.
  4. Aminoacyl synthase implements genetic code by acting as molecular dictionaries.
  5. Two initiation factors(eIF3 & eIF-1A) binds to 40S subunit of eukaryotic ribosome (80S).
  6. AUG serves as initiation codon for protein synthesis and codes for methionine
  7. Shine- Dalgarno sequence located -6 to -10bp from AUG codon. (purine rich).
  8. 3 sites on 80S Ribosome-
  • A site- new aminoacyl tRNA binds
  • P site- growing peptidyl chain present
  • E site- deacylated tRNA present.
  1. 2 ATPs are required for activation of amino acid.
  2.  There is no tRNA for hydroxyproline and hydroxylysine.

 

Don’t Forget to Solve all the previous Year Question asked on STEPS OF PROTEIN SYNTHESIS (Translation)

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