Transcription Lecture 2024/2025 - University of Hertfordshire PDF

Transcription 2 (Part B) Lecture 5 Dr. Nada K. Sedky Assistant Prof. of Biochemistry E-mail: [email protected] Office: L5.12 Semester A (2024/2025) Molecular Biology Adopted from Dr. Maria Braoudaki-UH-UK ...

Transcription 2 (Part B) Lecture 5 Dr. Nada K. Sedky Assistant Prof. of Biochemistry E-mail: [email protected] Office: L5.12 Semester A (2024/2025) Molecular Biology Adopted from Dr. Maria Braoudaki-UH-UK  Transcription – Part B Learning Objectives After attending the lecture and studying appropriate textbooks you should understand: The process of transcription in eukaryotic cells RNA processing Capping, Splicing, Polyadenylation  Transcription – Part B Flow of information from gene to polypeptide 1. Transcription 1. Transcription In Eukaryotes, mRNA is first In prokaryotes, 2. RNA processing being Transcription & Splicing transcribed in and translation 2. Translation the nucleus occur 3. Transport then it’s simultaneously translated in the cytoplasm 4. Translation 3. Protein Assembly 5. Protein Assembly  Transcription – Part B Reminder: Transcription in prokaryotic cells 1. RNA polymerase first needs to bind to sigma factor to be able to bind to the promotor and form a holoenzyme. 2. An open loop is obtained where the initiation starts. 3. Then, the elongation step occurs where RNA polymerase adds nucleotides towards the 3’ end. 4. Lastly, Termination of transcription is taking place by two different ways Rho dependent and Rho independent termination.  Transcription – Part B Prokaryotes vs Eukaryotes No membrane bound Membrane bound nucleus nucleus - Eukaryotes have nucleus, membrane bound organelles and - Prokaryotes are unicellular organisms that lack membrane organelles enclosed by plasma membrane. bound structures - With genes bound to the nucleus, eukaryotic cell must be - Prokaryotes have distinct cellular regions. In prokaryotic able to transport its mRNA to the cytoplasm and protect it cells, the DNA bundles together in a lesion called nucleoid. from degradation before being translated in the cytoplasm.  Transcription – Part B RNA polymerase; ≥10 subunits Ribosome components & protein synthesis All protein-coding genes RNA splicing, repression Translation control Protein synthesis Ribosome component RNA splicing Insertion of peptides into ER other unknown functions 6  Transcription – Part B Summary of the different types of RNAs produced in cells 7  Transcription – Part B A typical promoter in a eukaryotic cell… Transcription factors (TFIIs) recognize the promoter RNA polymerase II binds and forms the transcription initiation complex 8  Transcription – Part B …A typical promoter in a eukaryotic cell TATA box plays a role much like that of -10 element in bacteria. It is recognized by one of the transcription factors which eventually allows other transcription BRE is a sequence of 7 factors to bind to it. Also, contains lots of CAAT and GC box form nucleotides that is found As and Ts which makes it easier to pull parts of promotors and immediately upstream of the DNA strands apart. assist in binding different TATA box. It forms part of the promotor region as well. TFs Necessary for Found in many initiation promoters 9  Transcription – Part B Formation of the preinitiation complex Eukaryotic promoter TFs systematically fall into place on the DNA template, with each one further stabilizing the preinitiation complex and contributing to the recruitment of RNA polymerase II. General transcription factors bind TBP “TFII”; Transcription Factor for RNA polymerase II. Specified Preinitiation complex with the letters A–J.  Transcription – Part B TRANSCRIPTION: INITIATION  Transcription – Part B TRANSCRIPTION: ELONGATION Polymerase adds the nucleotides in the direction of 5’ to 3’ on the newly growing RNA strand Rate of Elongation: 1000 nucleotides / min at 37 oC  Transcription – Part B TRANSCRIPTION: TERMINATION The termination in Eukaryotes isn’t clearly understood as in prokaryotes RNA polymerase II transcribes a particular sequence (poly-adenylation sequence) at end of gene (often AAUAAA), then continues for 10-35 nucleotides, while proteins recognise sequence and cut RNA free.  Transcription – Part B Following Transcription eukaryotic RNA is processed Exons are the expressing regions. Introns are just intervening regions that aren’t expressed in the product. 14  Transcription – Part B Why is Eukaryotic RNA processed? 15  Transcription – Part B RNA processing: 1. Capping The CAP has two functions: 1) protects the RNA from degradation 2) It’s required for translation of the mRNA A cap is added to the 5’end at the carboxyl terminus. A cap consists of 7-methyl guanosyl residue linked to the transcript. 16  Transcription – Part B RNA processing: 2. Splicing; removal of introns and joining of exons GU–AG rule: Each intron will be cut at each end, and these ends almost always have GU at the 5’ end and AG at the 3’ end. Introns are removed from the primary transcript while RNA is still being synthesized and after the cap has been added, but before the transcript is transported into the cytoplasm 17  Transcription – Part B A eukaryotic intron in a pre-mRNA molecule forms a branched structure during RNA splicing. Splicing is carried out by a collective of RNA-protein complexes called small nuclear ribonuclear proteins (snRNPs) pronounced snurps. N.B: There are 5 snurps (u1, u2, u4,u5, u6). There is no u3 Lariat (removed intron) Mature mRNA  Transcription – Part B RNA Splicing Enzyme ❑snRNPs Small nuclear RNA proteins ❑ Spliceosome o Several snRNPs o Recognize splice site sequence o Cut & paste gene Intron  Transcription – Part B Summary Transcription in Eukaryotic cells is somehow different from that of prokaryotic cells. Eukaryotic cell must be able to transport its mRNA to the cytoplasm and protect it from degradation before being translated in the cytoplasm. Eukaryotic cells have 3 RNA polymerases, each comprising 10 or more subunits. Transcribed mRNA must undergo 3 processing steps: 5’capping, splicing and 3’polyadenylation. 20  Transcription – Part B MCQ 1 Which feature of promoters can be found in both prokaryotes and eukaryotes? A. GC box B. TATA box C. Octamer box D. -10 and -35 sequences B. TATA box 21  Transcription – Part B MCQ 2 Which pre-mRNA processing step is important for initiating translation? A. Poly-A tail B. RNA editing C. Splicing D. 7-methylguanosine cap D. 7-methylguanosine cap 22  Transcription – Part B MCQ 3 Which of the following best describes the 'cap' modification of eukaryotic mRNA? A. A modified guanine nucleotide added to the 3' end of the transcript. B. A modified guanine nucleotide added to the 5' end of the transcript. C. A string of adenine nucleotides added to the 3' end of the transcript. D. A string of adenine nucleotides added to the 5' end of the transcript. B. A modified guanine nucleotide added to the 5' end of the transcript. 23  Transcription – Part B MCQ 4 Which of the following does the abbreviation TBP stand for? A. TATA-box binding protein B. Transcription associated factor C. Transcription factor binding protein D. TATA box polymerase A. TATA-box binding protein 24  Transcription – Part B MCQ 5 What is the role of eukaryotic RNA polymerase I? A. Transcription of the major rRNA transcript. B. Transcription of mRNA only C. Transcription of mRNA, rRNA and tRNA. D. Transcription of 'small' RNAs including tRNAs, 5S RNAs and snRNAs. A. Transcription of the major rRNA transcript. 25  Transcription – Part B MCQ 6 Is the following statement true or false? 'Eukaryotic mRNA is transcribed by RNA polymerase II’. A. True B. False A. True. 26  Transcription – Part B MCQ 7 The promoter sequence in eukaryotes is A. TAATAA B. TATAAA C. TTGACA D. GTTAAA B. TATAAA 27  Transcription – Part B MCQ 8 In transcription, the nucleotide sequence CAT in DNA would specify _______________ in mRNA. A. GAU B. GUA C. CAT D. GTU B. GUA 28  Transcription – Part B Useful Textbooks for the Transcription Chapter; use any of these books or combinations of them Chapter 8 Chapter 8 Chapter 6 Transcription – Part B 30 Transcription – Part B 31  Transcription – Part B Thank You 32