Post transcriptional processing ppt BIOCHEMISTRY
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Post transcriptional processing ppt BIOCHEMISTRY

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  • Figure 30.17 Posttranscriptional modification of mRNA showing the 7-methylguanosine cap and poly-A tail.
  • FIGURE 26–21 Processing of pre-rRNAtranscripts in bacteria. 1 Before cleavage,the 30S RNA precursor is methylated atspecific bases. 2 Cleavage liberatesprecursors of rRNAs and tRNA(s). Cleavage atthe points labeled 1, 2, and 3 is carried outby the enzymes RNase III, RNase P, andRNase E, respectively. As discussed later in thetext, RNase P is a ribozyme. 3 The final 16S,23S, and 5S rRNA products result from theaction of a variety of specific nucleases. Theseven copies of the gene for pre-rRNA in theE. coli chromosome differ in the number,location, and identity of tRNAs included inthe primary transcript. Some copies of thegene have additional tRNA gene segmentsbetween the 16S and 23S rRNA segments andat the far 3 end of the primary transcript.
  • Figure 30.15 Posttranscriptional processing of eukaryotic ribosomal RNA by ribonucleases (RNases).
  • FIGURE 26–23 Processing of tRNAs in bacteria and eukaryotes. Theyeast tRNATyr (the tRNA specific for tyrosine binding; see Chapter 27)is used to illustrate the important steps. The nucleotide sequencesshown in yellow are removed from the primary transcript. The endsare processed first, the 5 end before the 3 end. CCA is then addedto the 3 end, a necessary step in processing eukaryotic tRNAs andthose bacterial tRNAs that lack this sequence in the primary transcript.While the ends are being processed, specific bases in the rest of thetranscript are modified (see Fig. 26–24). For the eukaryotic tRNAshown here, the final step is splicing of the 14-nucleotide intron. Intronsare found in some eukaryotic tRNAs but not in bacterial tRNAs.
  • FIGURE 26–23 Processing of tRNAs in bacteria and eukaryotes. Theyeast tRNATyr (the tRNA specific for tyrosine binding; see Chapter 27)is used to illustrate the important steps. The nucleotide sequencesshown in yellow are removed from the primary transcript. The endsare processed first, the 5 end before the 3 end. CCA is then addedto the 3 end, a necessary step in processing eukaryotic tRNAs andthose bacterial tRNAs that lack this sequence in the primary transcript.While the ends are being processed, specific bases in the rest of thetranscript are modified (see Fig. 26–24). For the eukaryotic tRNAshown here, the final step is splicing of the 14-nucleotide intron. Intronsare found in some eukaryotic tRNAs but not in bacterial tRNAs.
  • Figure 30.16 A. Primary tRNA transcript. B. Functional tRNA after posttranscriptional modification. Modified bases include D (dihydrouracil), ψ (pseudouracil), and m, which means that the base has been methylated
  • Figure 30.19 Alternative splicing patterns in eukaryotic mRNA
  • FIGURE 26–20 Alternative processing of the calcitonin gene transcriptin rats. The primary transcript has two poly(A) sites; one predominatesin the brain, the other in the thyroid. In the brain, splicingeliminates the calcitonin exon (exon 4); in the thyroid, this exon is retained.The resulting peptides are processed further to yield the finalhormone products: calcitonin-gene-related peptide (CGRP) in thebrain and calcitonin in the thyroid.

Post transcriptional processing ppt BIOCHEMISTRY Post transcriptional processing ppt BIOCHEMISTRY Presentation Transcript

  • POST TRANSCRIPTIONAL PROCESSING GENETIC CODE
  • POST TRANSCRIPTIONAL PROCESSING Primary transcript made by RNA polymerase normally undergo further alteration, called post transcriptional processing
  • POST TRANSCRIPTIONAL PROCESSING
  • POST TRANSCRIPTIONAL PROCESSING
  • POST TRANSCRIPTIONAL PROCESSING Different types of processing Cleavage of precursor of RNA Terminal addition of nucleotides Base modification Splicing
  • POST TRANSCRIPTIONAL PROCESSING Prokaryotic mRNA is not post transcriptionally processed
  • POST TRANSCRIPTIONAL mRNA PROCESSING mRNA processing 5’ capping Addition of poly A tail Splicing
  • POST TRANSCRIPTIONAL mRNA PROCESSING 5’ capping Poly A tail
  • POST TRANSCRIPTIONAL mRNA PROCESSING SPLICING SnRNPs
  • POST TRANSCRIPTIONAL mRNA PROCESSING
  • POST TRANSCRIPTIONAL rRNA PROCESSING PROKARYOTIC rRNA processing
  • POST TRANSCRIPTIONAL rRNA PROCESSING EUKARYOTIC rRNA processing
  • POST TRANSCRIPTIONAL tRNA PROCESSING tRNA PROCESSING Cleavage of a 5’ leader sequence Splicing to remove intron Replacement of 3’terminal UU by CCA Modification of several bases
  • POST TRANSCRIPTIONAL tRNA PROCESSING
  • POST TRANSCRIPTIONAL tRNA PROCESSING
  • ALTERNATE SPLICING
  • ALTERNATE SPLICING
  • RNA EDITING A change in the base sequence of RNA after transcription by process other than RNA splicing is called RNA editing
  • RNA EDITING ApoB-48 ApoB-100 ApoB gene Transcription CAA5’ 3’ Unedited mRNA NH4 RNA editing by deaminase 5’ 3’ UAA Translation in intestine Translation in liver 4536 amino acids 2152 amino acids
  • INHIBITORS OF RNA SYNTHESIS Binds to DNA Actinomycin D Binds to β subunit of prokaryotic RNA polymerase Rifampicin Inhibits eukaryotic RNA polymerase α-Amanitin
  • REVERSE TRANSCRIPTION
  • GENETIC CODE The genetic code is the system of nucleotide sequences of mRNA that designates particular amino acid sequences in the process of translation
  • GENETIC CODE The genetic code is in the form of CODONS. CODONS are a group of three adjacent bases that specify the amino acids of protein
  • GENETIC CODE
  • CHARACTERISTICS OF GENETIC CODE Number of codons Stop or nonsense codons Code is degenerate but unambiguous The code is almost universal The code is non- overlapping
  • Codon- anticodon recognition
  • Codon- anticodon recognition
  • WOBBLE HYPOTHESIS  The first 2 bases of codons are same, third is different, “wobble”  Wobble allows some tRNAs to recognize more than one codon