rna processing in prokaryotes and eukaryotes.pptx

This pot is all aboit rna processing.

1. RNA PROCESSING SUBMITTED BY :- Ankita Sunani Registration no:22MSZOLG49

2. WHAT IS RNA PROCESSING? RNA processing prepares the transcript (the product of transcription) so it can function in translation or protein synthesis. As such, it takes place after transcription and before translation.
When it is newly formed and unprocessed, “pre-” is attached to the name of the transcript: pre-mRNA, pre- tRNA , and pre- rRNA . After processing, the transcript is said to become “mature”, meaning it is ready for protein synthesis.

3. TYPES OF RNA Involved in rna processing Messenger RNA (mRNA): produced during transcription, this molecule contains the protein information of the gene that was encoded in DNA and will be used as a template in translation.
Transfer RNA ( tRNA ): decodes mRNA into a protein during translation.
Ribosomal RNA ( rRNA ): makes up the core of the ribosome, the organelle in which protein synthesis takes place.

4. STEPS INVOLVED IN RNA PROCESSING It involves several steps, including capping, splicing, and polyadenylation.

5. CAPPING: This is the first processing event an mRNA undergoes before translation. Capping is the process of adding a 7-methylguanosine cap to the 5’ end of the primary transcript by phosphate linkage. Three enzymes are involved in this process – 7-methyltransferase, RNA triphosphatase and guanylyltransferase . The process of capping is initiated by the removal of phosphate groups from the terminal nucleotide to create a site for the addition of the methylated guanine residues. Guanylyltransferase first adds guanine residues to the site created (the 5’ terminal), which is then followed by the addition of methyl groups by the enzymes methyltransferases .

6. TAILING: Tailing, also known as polyadenylation, is the process of cleavage of the 3’ end and addition of adenylate residues to the same end of the pre-mRNA. A conserved sequence 5’-AAUAAA-3′ is present near the 3’ end of the primary transcript that is a polyadenylation signal sequence. The endonucleolytic cleavage takes place 10-30 base pairs down this signal sequence, leaving the AAUAAA sequence in the transcript. A  GU  rich region is also present downstream this signal sequence that helps in cleavage and polyadenylation. The enzyme poly-A polymerase then adds adenine nucleotides (200-250 in number) to the cleaved pre-mRNA. This addition of adenine residues is called poly-A tailing or polyadenylation.

7. SPLICING: There are many non coding sequences present in the primary transcript that can intervene in the process of translation. The removal of these non-coding sequences (known as introns) and the reattachment of the coding sequences into a continuous molecule is the process of splicing. The coding sequences are referred to as exons. The whole splicing mechanism takes place by recruitment of the spliceosome machinery. This machinery consists of proteins and small nuclear RNAs (snRNA) that recognise the splicing sites. In eukaryotes, the pre- mRNAs  are spliced in various combinations to produce different mature RNAs, this process is referred to as alternative splicing.

8. rRNA PROCESSING: In eukaryotes, rRNA processing takes place primarily in the nucleolus, a specialized region within the nucleus where ribosomal subunits are assembled. The process involves several steps, including: Transcription : rRNA genes are transcribed by RNA polymerase I, resulting in a long precursor RNA molecule called pre- rRNA . 2. Cleavage : Pre- rRNA undergoes several cleavage events that generate the mature rRNA molecules. In eukaryotes, the 45S pre- rRNA precursor is cleaved into three separate rRNAs : the 18S, 5.8S, and 28S rRNAs . The cleavage events are catalyzed by a large ribonucleoprotein complex called the small nucleolar ribonucleoprotein ( snoRNP ) complex, which guides the ribonucleases to the specific cleavage sites.

9. 3. Modification : rRNA molecules are heavily modified by enzymes that add and remove specific chemical groups from the RNA molecule. These modifications include methylation, pseudouridylation , and others. These modifications help stabilize the rRNA structure and regulate ribosome activity. 4. Assembly : The mature rRNA molecules are assembled with ribosomal proteins to form the two subunits of the ribosome. The small subunit contains the 18S rRNA and the large subunit contains the 5.8S, 28S, and 5S rRNAs . In prokaryotes, rRNA processing occurs in a similar but simpler way compared to eukaryotes. There is no nucleolus, and the rRNA genes are transcribed by RNA polymerase alone. The primary transcript undergoes several cleavage events and modification steps, leading to the formation of the mature rRNA molecules.

10. tRNA PROCESSING: Transcription: tRNA genes are transcribed by RNA polymerase III, producing precursor tRNA molecules. Removal of leader and trailer sequences: Non-functional leader and trailer sequences are removed from precursor tRNAs . Addition of CCA sequence: The 3' end of tRNA molecules is modified by adding a CCA sequence, which serves as the attachment site for amino acids. Modification of bases: Bases within the tRNA molecule undergo various modifications for stability and proper functioning. Splicing (in some cases): Some tRNA precursors contain introns, which are non-coding regions that need to be removed through splicing. Quality control and proofreading: tRNA molecules undergo quality control mechanisms to ensure proper folding and functionality.

11. Once processed, mature tRNA molecules participate in protein synthesis by delivering specific amino acids to the ribosome.

12. RNA processing is necessary for the production of functional mRNA molecules that can be efficiently translated into proteins. It enables the removal of non-coding regions, generation of mRNA diversity, addition of important modifications, and regulation of gene expression, thereby playing a vital role in shaping the proteome of a cell and maintaining its proper function. IMPORTANCE OF RNA PROCESSING:

13. RECENT ADVANCEMENTS

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