Translation in prokaryotes central dogma

Translation in prokaryotes
Central dogma, ribosomes, initiation, elongation, termination.

1. PG DEPARTMENT OF BIOTECHNOLOGY SAHYADRI SCIENCE COLLEGE, SHIVAMOGGA-577203 A SEMINAR REPORT ON “ TRANSLATION IN PROKAYOTES” UNDER THE GUIDENCE OF Dr . Prabhakar BT Associate Professor PG Department of Biotechnology Sahyadri Science College Shivamogga-577203 SUBMITTED BY M.JYOTHIKA 1 ׀ MSc ׀ 1SEM PG Department of Biotechnology Sahyadri Science College Shivamogga-577203

2. CONTENTS INTRODUCTION CENTRAL DOGMA PROTEIN SYNTHESIS INITIATION ELONGATION TERMINATION OVERVIEW OF TRANSLATION

3. INTRODUCTION It is the process of synthesis of protein from messenger RNA transcripts (mRNA) after the process of transcription of DNA to RNA It place in the cytoplasm by specialised organelle known as ribosome. There are no endoplasmic reticulum in the prokaryotes and ribosomes are suspended in the cytoplasm, whereas endoplasmic reticulum are present in eukaryotes which harbors ribosomes-translation takes place on rough endoplasmic reticulum (RER) in eukaryotes, whereas translation occurs freely in cytoplasm in the prokaryotes. The codons on the mRNA are translated into amino acid sequence which leads to the synthesis as protein. Translation requires a variety of cellular components, such as proteins, RNAs and different small molecules. It has also three main steps: Initiation- Formation of mRNA-ribosome complex Elongation- Formation of polypeptide chain complimentary to the mRNA Termination- Termination of polypeptide chain.

4. CENTRAL DOGMA Flow of genetic information on a cell -How do we move information from DNA to proteins? “It states that genetic information is transmitted from DNA to RNA to Protein and this information cannot be transferred back from protein to either protein or nucleic acid”.

5. WOBBLE HYPOTHESIS There are more than one codon for one amino acid. This is called degeneracy of genetic code. To explain the possible cause of degeneracy of codons, in 1966, Francis Crick proposed “the wobble hypothesis”. According to this hypothesis, only the first two bases of the codon have a precise pairing with bases of the anticodon of tRNA, while the pairing between the third bases of codon and anticodon may wobble(wobble means to sway or move unsteadily). The phenomenon permits a single tRNA to recognize more than one codon. therefore, although there are61 codons for amino acids, the number of tRNA is far less(around40) which is due to wobbling.

6. RIBOSOMES It is made up of rRNA and proteins. 70s ribosome occur in prokaryotic cells. It consists of two subunit smaller(30s) and larger(50s). Larger subunit consists of three site: A site, P site, E site.

7. 30S RIBOSOMAL SUBUNIT 30s subunit, is the smaller subunit of the 70s ribosome found in prokaryotes. It is the complex of the 16s ribosomal RNA (rRNA) and 19 proteins.

8. 50S ribosomal SUBUNIT 50s is the larger subunit of the 70s ribosome of prokaryotes, i.e. bacteria and archaea.

9. Transfer RNA It contains three structural loops joined by hydrogen bonding. Transfer RNA brings or transfers amino acids to the ribosomes.

10. VARIOUS PROTEINS FACTORS INVOLVED IN PROTEIN SYNTHESIS FACTORS IF-1 IF-2 IF-3 EF-TU EF-TS EF-G RF-1 TRANSLATION STEPS INITIATION INITIATION INITIATION ELONGATION ELONGATION ELONGATION TERMINATION FUNCTIONS Helps to stabilize 30s ribosomal subunit Binds Fmet -tRNA withs30s subunit mRNA complex; bind GTP and hydrolyse. Binds 30s subunit with mRNA Binds GTP; bring Aminoacyl-tRNA to A site of ribosome Generates EF-TU Helps in translocation of ribosome Helps to dissociates polypeptide from tRNA ribosome complex; specific for UAA and UGA

11. RF-2 RF-3 TERMINATION TERMINATION Helps to dissociates polypeptide; specific for UGA and UAA Stimulates RF-1 and RF-2

12. PROTEIN SYNTHESIS Three steps ; Initiation: It brings together mRNA, ribosomal subunits and initiator tRNA. Elongation: In this phase, adding of amino acids take place based on codon sequence. Termination: Here codon ends and translation stops

13. ACTIVATION OF AMINO ACID The activation of amino acids take place in cytosol. The activation of amino acids is catalysed by their aminoacyl tRNA synthetases. All the 20 amino acids are activated and bound to 3’ end of their specific tRNA in the presence of ATP and Mg++.

14. 1 . INITIATION translation Initiation of translation in prokaryotes involves the assembly of the components of the translation system which are: The two ribosomal subunits (small and large) The mRNA to be translated,

15. 2.ELONGATION TRANSLATION Elongation begins after the formation of the initiation complex. Elongation means length of polypeptide chain in increasing. This process complete in three steps Binding of aminoacyl tRNA to A site Peptide bond formation Ribosomal Translocation There are three elongation factor involve: EF-Tu, EF-Ts, EF-G

16. Binding of amino acyl tRNA to a site The 2 nd tRNA carrying next amnio acid comes into A site and recoginse the codon mRNA. This binding is facilitated by EF-Tu-GDP.

17. PEPTIDE BOND FORMATION T he amino acid present in tRNA of P-site, F met is transferred to tRNA of A-site forming peptide bond. This reaction is catalysed by peptidyl transferase Now, the tRNA at P-site become uncharged

18. RIBOSOME TRANSLOCATION After peptide bond formation ribosome moves one codon ahead along 5’-3’ direction on mRNA, so that dipeptide-tRNA appear on P-site and next codon appear on A-site. The uncharged tRNA exit from ribosome and enter to cytosol.

19. 3.TERMINATION OF TRANSLATION This is last phase of translation. Termination occurs when one of the three termination codons moves into the A-site. These codons are not recognized by proteins called release factors, namely RF1 Step 1 – After the amino acids needed to make the protein required are properly bonded to each other a release factors binds to the complex when a stop codon enters the A site . Step 2 – The release factor then disconnects the polypeptide from the tRNA in the P site . Step 3 – The remaining components mRNA, ribosomal subunit, and the protein are released and the process of translation ends

20. OVERVIEW OF TRANSLATION

21. CONCLUSION Prokaryotic translation is a highly regulated and intricate process essential for protein synthesis with in these simple cells. Translational initiation, elongation, and termination are coordinated through the interaction of ribosomal RNA and proteins, with messenger RNA providing the template for protein assembly. The involvement of initiation factors, elongation factors, and release factors, alongside other factors, ensures the precision and efficiency of this process. However, despite its complexity, prokaryotic translation remains a vital component of cellular function and is a target for regulation in response to various environmental cues.

22. REFERENCES Willey J., Sherwood L., Woolverton C.J. 2017. Prescott’s Microbiology 10 th Edition, McGraw Hill publication, New York, USA Kerbs J.E., Goldstein E.S,. Kilpatrick S.T. 2017. Lewis Genes X11. jones and Bartlett publishers, Inc., Burlington, MA, USA