lecture 6.pdf

RNA structure Lecture 6 w of nucleotides At the end of this lecture, students should be able to: • Understand different types of RNA molecules. • Recognize the role of RNA polymerase enzymes in RNA synthesis. 5 3 G E C A Fut O O O 0 o phospho difford ribose ja m Idol's double s...

RNA structure Lecture 6 w of nucleotides At the end of this lecture, students should be able to: • Understand different types of RNA molecules. • Recognize the role of RNA polymerase enzymes in RNA synthesis. 5 3 G E C A Fut O O O 0 o phospho difford ribose ja m Idol's double strand signal strand Types of RNA RNA can largely be divided into two types: Coding RNA that carries the code for making proteins • messenger RNA (mRNA) Non -coding RNA (ncRNA), divided according to the length of the RNA or on the function • S hort ncRNAs (~ 20 – 30 nt ), which include microRNAs (miRNAs), and small interfering (siRNAs). • S mall ncRNAs up to 200 nt , which include transfer RNA (tRNA), small nuclear RNA (snRNA), and small nucleolar RNA (snoRNA). • L ong ncRNAs ( > 200 nt ), which include ribosomal RNA (rRNA), enhancer RNA ( eRNA ) and long intergeneic ncRNAs (lincRNAs) 5 3 Protein ite it 6 a I é Te a m t ahi.no acids common codon BIASI IN MANI noncoded MRNA 1 Short small long rRNA miRNA SiRNA tRNA Sn RNA ERNA snoRNA line RNA two g 5 The three main types of RNA directly involved in protein synthesis are: messenger RNA (mRNA), carries the message from the DNA. ribosomal RNA (rRNA), part of ribosomes. transfer RNA (tRNA ), carries amino acids. transcription wt 0Wh DNA RHINO's coding RNA g ma __ M long ncRNA Synth inside nucleolus translation't 31090 25 000000 Ld apt tRNA and rRNA are encoded by the DNA, where they are transcribed into long RNA molecules that are subsequently cut to release smaller fragments containing the individual mature RNA species . In eukaryotes, synthesis, cutting, and assembly of rRNA into ribosomes takes place in the nucleolus. Ribosomes assembly requires the activity of numerous snoRNAs y synthesized as long chain Pre tRNA Pre rRNA then cut into shorter 0 Foot Small nucleolar RNA rRNA composes up to about 60 % of the ribosome by mass and providing the location where the mRNA binds . The rRNA ensures the proper alignment of the mRNA, tRNA, and the ribosomes ; the rRNA of the ribosome also has an enzymatic activity (peptidyl transferase) and catalyzes the formation of the peptide bonds between two aligned amino acids during protein synthesis O mat n É irRNA Is 160 mass ribosome Proper alignment MRNA tRNA ribosome enzymatic activity peptidyl transferase 5 peptide't bond fixing tRNA mRNA in their places tRNAs are usually only 70 – 90 nucleotides long, they have a distinctive folded structure with three hairpin loops that form the shape of a three -leafed clover . One of these hairpin loops contains a sequence called the anticodon, which can recognize and decode an mRNA codon . Each tRNA has its corresponding amino acid attached to its 3 `end . 00 I and ait ED A A ZEN MRNA snRNAs function as ribozymes during the process of intron removal from mRNA sequences. Other small ncRNA and lncRNA molecules play a role in the regulation of transcriptional and translational processes. miRNAs, pair with mRNA regions and target them for degradation by specific proteins. Iiakudear ng or I Pre RNA needs to be sliced by nybozyn Si RNA Mi RNA ARNA 84 50 IAN ibid pan marking for degradation The principal enzyme responsible for RNA synthesis is RNA polymerase , which catalyzes the polymerization of ribonucleotide triphosphates (NTPs) as directed by a DNA template . The synthesis of RNA is similar to that of DNA, and like DNA polymerase, RNA polymerase catalyzes the growth of RNA chains always in the 5 ′ to 3 ′ direction . Unlike DNA polymerase . RNA polymerase does not require a preformed primer to initiate the synthesis of RNA . Instead, transcription initiates de novo at specific sites at the beginning of genes . The initiation process is particularly important because this is a major step at which transcription is regulated . bind mrna and g for gred n EEE Eic Iss In eukaryotic cells, three RNAPs share the task of transcription, the first step in gene expression. RNA Polymerase I (Pol I) is responsible for the synthesis of the majority of rRNA transcripts, RNA Polymerase III (Pol III) produces short, structured RNAs such as tRNAs and 5S rRNA . RNA Polymerase II (Pol II) produces all mRNAs and most regulatory and untranslated RNAs . RNA polymerases require the recognition of promoter sites to initiate RNA synthesis. RNA polymerases require additional proteins (general transcription factors) to initiate transcription. The recruitment of RNA polymerase II to promoters requires a minimum of five general transcription factors. Other factors are required for RNA polymerases I and III to bind their promoters n age I small nucleolar RNAs (snoRNAs) that function in pre -rRNA processing . The snoRNAs are complexed with proteins, forming small ribonucleoprotein particles that are called snoRNPs . Pre -tRNA will also be processed by cleavage at 3 ` and 5` ends, addition of CCA to 3` end and modification of several nitrogen base s snoRNA a to nucleolus ton RNA contain thy amine TRNA I rRNA HI tRNA 58 Ms.MRNA J É