1. LECTURE CONNECTIONS 13 | Transcription © 2009 W. H. Freeman and Company

2. Chapter 13 Outline 13.1 RNA Consisting of a Single Strand of Ribonucleotides Participates in a Variety of Cellular Functions 13.2 Transcription Is the Synthesis of an RNA Molecule from a DNA Template 13.3 The Process of Bacterial Transcription Consists of Initiation, Elongation, and Termination 13.4 The Process of Eukaryotic Transcription Is Similar to Bacterial Transcription but Has Some Important Differences 13.5 Transcription in Archaea Is More Similar to Transcription in Eukaryotes than to Transcription in Eubacteria

3. 13.1 RNA Consisting of a Single Strand of Ribonucleotides Participates in a Variety of Cellular Functions RNA is polymer consisting of nucleotides joined together by ________________________ bonds. RNA has a free hydroxyl group on the ___’ carbon atom of the ribose sugar. RNA is degraded rapidly under alkaline conditions. RNA’s pyrimidines are cytosine and URACIL. RNA is usually single stranded.

4. Primary structure Secondary structure RNA molecules can assume different structures. The Structure of RNA

6. Classes of RNA Ribosomal RNA – rRNA Messenger RNA – mRNA: carries the coding instructions for polypeptides chains from DNA to ribosomes. Pre-messenger RNAs (pre-mRNAs or nRNAs): the intermediate product of transcription in eukaryotes cells. Transfer RNA – tRNA: serve as the link between the coding sequence of nucleotides in the mRNA and the amino acid sequence of a polypeptide chain.

7. Classes of RNA Small nuclear RNAs – snRNAs: some participate in the processing of RNA. MicroRNAs – miRNAs: carry out RNA interference (RNAi) Small interfering RNAs – siRNAs: triggers degradation of other RNA molecules

8. 13.2 Transcription Is the Synthesis of an RNA Molecule from a DNA Template Only the gene (s) of interested are transcribed into RNA. Transcription is a highly selective process. Transcription requires: - DNA template - a raw materials needed to build a new RNA molecule - the transcription apparatus

9. The Template The transcribed strand: template strand. During transcription, an RNA molecule that is complementary and antiparallel to the DNA template strand is synthesized.

10. The Template The transcription unit Promoter: is a DNA sequence that the transcription apparatus recognizes and binds. RNA-coding sequence: a sequence of DNA nucleotides that is copied into a RNA molecule Terminator: a sequence of nucleotides that signals where transcription is to end.

11. The transcription apparatus is said to move downstream during transcription: it binds to the promoter (which is usually upstream of the start site) and moves toward the terminator (which is downstream of the start site). The first nucleotide transcribed is numbered +1. Nucleotides upstream of the start site are assigned negative numbers.

12. Concept Check 1 Which of the following phrases does not describe a function of the promoter? a.Serves as sequences to which the transcription apparatus binds b.Determines the first nucleotide that is transcribed into RNA c.Determines which DNA strand is template d.Signals where transcription ends

13. Initiation The substrate for transcription: Ribonucleoside triphosphates – rNTPs added to the 3′ end of the RNA molecule Nucleotides are added one at a time to the 3’-OH group of the growing RNA molecule. Two phosphate groups are cleaved from the incoming rNTP; the remaining phosphate group participates in a phosphodiester bond that connects the nucleotide to the growing RNA molecule.

14. Initiation The transcription apparatus: Bacterial RNA polymerase: five subunits made up of the core enzyme: Two copies of α Single copy of β Single copy of β′ A stabilize enzyme: ω The sigma  factor: binding to the promoter when transcription starts

15. Initiation The transcription apparatus: Eukaryotic RNA polymerases