The Central DogmaSlide 2Chapter 16 (i): Overview of TranscriptionThe Basics of TranscriptionSlide 5Characteristics of RNA PolymeraseSlide 7Initiation: How Does Transcription Begin?What Role Does Sigma Play in Initiation?Bacterial PromotersSlide 11Eukaryotic PromotersIn Bacteria, Sigma Subunits Initiate TranscriptionWhat Occurs Inside the Holoenzyme in Bacteria?Slide 15Slide 16Elongation and TerminationSlide 18MB- Transcribe to a mRNA? Little tricky!RNA Processing in EukaryotesThe Discovery of Eukaryotic Genes in PiecesSlide 22RNA SplicingSlide 24Adding Caps and Tails to RNA TranscriptsTranscription and Translation in BacteriaSlide 27Transcription and Translation in EukaryotesSlide 29Visualizing the Central Dogma© 2011 Pearson Education, Inc.The Central DogmaThe sequence of bases in a particular stretch of DNA specifies the sequence of bases in an RNA molecule, which specifies the sequence of amino acids in a protein. In this way, genes ultimately code for proteins.The central dogma summarizes the flow of information in cells. It states that DNA codes for RNA, which codes for proteins: DNA  RNA  proteins© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Chapter 16 (i): Overview of Transcription•The first step in converting genetic information into proteins is transcription, the synthesis of an mRNA version of the instructions stored in DNA.•RNA polymerase performs this synthesis by transcribing only one strand of DNA, called the template strand. •The other DNA strand is called the non-template, or coding strand, which matches the sequence of the mRNA, except that RNA has uracil (U) in place of thymine (T).© 2011 Pearson Education, Inc.The Basics of Transcription• Of the 2 DNA strands, one acts as the template (3’Of the 2 DNA strands, one acts as the template (3’5’ strand).5’ strand).This strand is called the ‘This strand is called the ‘template strandtemplate strand’, ’, antisense strand antisense strand or or ((--) ) strandstrand..• The other is called the ‘coding strand’, The other is called the ‘coding strand’, sense strand sense strand or (or (++) strand. ) strand. Sometimes it is called the ‘non-template strand’!Sometimes it is called the ‘non-template strand’!is archived inbase sequences ofDNAGENETIC INFORMATIONGenesEXPRESSEDText sectionwhere youcan find moreinformationconsists offunctional units called13.2Genotypemake upcan bemay regulatewhether genesif firstTRANSCRIBED byRNA polymerase16.14.3to formRNA4.215.115.217.1–418.1–4© 2011 Pearson Education, Inc.Characteristics of RNA PolymeraseLike the DNA polymerases, an RNA polymerase performs a template-directed synthesis in the 5′ to 3′ direction. But unlike DNA polymerases, RNA polymerases do not require a primer to begin transcription.•Bacteria have one RNA polymerase while eukaryotes have three distinct types, RNA polymerase I, II, and III.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Initiation: How Does Transcription Begin?•Initiation is the first phase of transcription.–However, RNA polymerase cannot initiate transcription on its own.–Sigma, a protein subunit, must first bind to the polymerase.© 2011 Pearson Education, Inc.What Role Does Sigma Play in Initiation?•Sigma and RNA polymerase together form a holoenzyme, an enzyme made up of a core enzyme and other required proteins. •Prokaryotic RNA polymerase is a holoenzyme made up of the core enzyme, which has the ability to synthesize RNA, and a sigma subunit.–Sigma acts as a regulatory factor, guiding RNA polymerase to specific promoter sequences on the DNA template strand.© 2011 Pearson Education, Inc.Bacterial Promoters•Bacterial promoters are comprised of 4050 base pairs and have two key regions. •The –10 box is found 10 bases upstream (in the opposite direction of RNA polymerase movement during transcription) from the transcription start site (the +1 site) and consists of the sequence TATAAT.•The –35 box, consisting of the sequence TTGACA, is 35 bases upstream from the +1 site. •All bacterial promoters have a –10 box and a –35 box, the remainder of the promoter sequence varies.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Eukaryotic Promoters•Eukaryotes have a much more diverse and complex series of promoters than do prokaryotes.•Many of the eukaryotic promoters include a unique sequence called the TATA box, centered about 30 base pairs upstream of the transcription start site.© 2011 Pearson Education, Inc.In Bacteria, Sigma Subunits Initiate Transcription•Transcription begins when sigma, as part of the holoenzyme complex, binds to the –35 and –10 boxes. •Sigma, and not RNA polymerase, makes the initial contact with DNA that starts transcription, supporting the hypothesis that sigma is a regulatory protein.•Most bacteria have several types of sigma proteins.–Each type allows RNA polymerase to bind to a different type of promoter and therefore a different kind of gene.© 2011 Pearson Education, Inc.What Occurs Inside the Holoenzyme in Bacteria?•Sigma opens the DNA double helix and the template strand is threaded through the RNA polymerase active site. •An incoming ribonucleoside triphosphate (NTP) pairs with a complementary base on the DNA template strand, and RNA polymerization begins.•Sigma dissociates from the core enzyme once the initiation phase of transcription is completed.© 2011 Pearson Education, Inc.Holo enzyme?Core enzyme?Rudder?Zipper?© 2011 Pearson Education, Inc.During elongation, RNA polymerase has three prominent channels, or grooves. These channels provide sites for ???© 2011 Pearson Education, Inc.Elongation and Termination•During the elongation phase of transcription, RNA polymerase moves along the DNA template and synthesizes RNA in the 5'  3' direction.•Transcription ends with a termination phase. In this phase, RNA polymerase encounters a transcription termination signal in the DNA template. •In bacteria the transcription termination signal codes for RNA forming a hairpin structure, which causes the RNA polymerase to separate from the RNA transcript, ending transcription.•RNA polymerases do not proofread and correct mistakes.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.MB- Transcribe to a mRNA? Little tricky!© 2011 Pearson Education, Inc.RNA Processing in Eukaryotes•In bacteria, the information in DNA is converted to mRNA directly. In