Transcription MBC 223 1446 PDF

Transcription Dr. Ayaz K. Mallick This PowerPoint is to illustrate the lectures and should not be used as a substitute for textbooks. You must read the recommended textbooks for complete understanding and preparation for the exams.  Learnin...

Transcription Dr. Ayaz K. Mallick This PowerPoint is to illustrate the lectures and should not be used as a substitute for textbooks. You must read the recommended textbooks for complete understanding and preparation for the exams.  Learning Objectives At the end of the lecture, the students should be able to Define translation Describe the steps of initiation, elongation, and termination in transcription Compare and contrast the steps of transcription in eukaryotes and prokaryotes List the inhibitors of transcription Describe the post-transcriptional modification process  Transcription Transcription is a process of mRNA (messenger RNA) synthesis from DNA (gene) The enzyme responsible for this process is RNA polymerase  Transcription RNA polymerase binds to the promoter region of a gene Only one of the DNA strands is transcribed The strand varies from gene to gene A complementary strand of RNA, called messenger RNA (mRNA), is produced from the DNA template RNA polymerase synthesizes RNA by attaching nucleotides in the 5’ → 3’ direction Transcription steps (In Prokaryotes) 1. Chain initiation 2. Chain elongation 3. Chain termination  Chain Initiation RNA synthesis is initiated only at specific sites on the DNA known as promoter regions Pribnow box - 35 sequence The strand of DNA gives rise to mRNA is called as Transcribed strand /Template strand / anti-sense strand / non-coding strand It has sequence complementary to that of RNA The other strand of DNA is called as Non-template /sense strand / coding strand Sequence is same as that of RNA  v1 o The sense (non-template) strand sequences of selected E. coli (prokaryotes) promoters  Chain Elongation DNA at the origin site of transcription unwinds forming a transcription bubble RNA polymerase synthesizes the RNA This forms the RNA-DNA hybrid RNA chain elongation by RNA polymerase  Chain Termination Occurs at the termination site Two types of termination Rho dependent (requires rho protein) 3595820 Rho independent ( intrinsic) it Twins Transcription is terminated at a sequence of 4-10 AT base pairs These AT base pairs are present after a GC rich region Rho independent or intrinsic termination  Transcription in Eukaryotes Eukaryotes have multiple RNA polymerases ✓RNA polymerase I (produces rRNA) ✓RNA polymerase II (produces mRNA) ✓RNA polymerase III (produces tRNA and some rRNA) Particals small  Transcription in Eukaryotes Chain Initiation thy 3W Eukaryotic genes contain promoter (TATA box / CCAAT box) and enhancer sequences They require transcription factors (proteins) that recognize promoter and enhancer sequences Chain Elongation Same as in prokaryotes Chain Termination Eukaryotic genes have no termination sequences like prokaryotes RNA polymerase II makes extra mRNA up to 1000 to 2000 nucleotides more at the 3’ end before termination  Inhibitors of Transcription Rifampicin Bactiva aw _stB  Antibiotic used as anti-tuberculosis drug  Binds to prokaryotic RNA polymerase and prevents chain elongation α-Amanitin  a potent toxin produced from mushrooms  Binds tightly to eukaryotic RNA polymerase II  Post-Transcriptional Modifications (RNA Processing) In prokaryotes, the mRNA is ready to synthesize protein In eukaryotes, the nascent mRNA is modified after transcription (post-transcriptional modifications) to produce mature mRNA The modified mRNA moves out of the nucleus and into the cytoplasm for translation FWIWRNA W 703,4 1. Capping is sit I ie 2. Polyadenylation- Addition of Poly A tail 3. Splicing-removal of introns ones III weibo.tt To wantes T.IM  1. Capping head Addition of a methylated guanine nucleotide at 5’ end of mRNA Function: To prevent mRNA degradation of exonuclease enzymes 2. Polyadenylation Addition of a poly A tail (polyAdenylate…AAA…) at 3’ end of mRNA Function: To protect the mRNA from degradation For ribosomal RNA recognition  3. Splicing (Removal of Introns ) Function: To make mRNA active for translation w ̅ I  Eukaryotes vs Prokaryotes (Transcription Differences) Overall, the process of transcription in eukaryotes is similar to that of prokaryotes But there are differences ! Eukaryotes vs Prokaryotes (Transcription Differences)  i3tpw II WI ̅ Layaway www.dt.ws DNA II histamin Web