1. Transcription
How the Information in DNA Is Used to Produce RNA in Prokaryotes and Eukaryotes

2. Information Flow From DNA
replication
DNA
transcription
RNA
translation
Protein

3. Components of RNA Nucleotides
Purine bases
Adenine (A)
Guanine (G)
Pyrimidine bases
Cytosine (C)
Uracil (U)
5-carbon sugar
Ribose
Phosphate
PO4

4. RNA Structure Primary Structure Chain of Nucleotides
Secondary Structure
Single folded chain
RNA to RNA
base pairing rules:
G pairs with C
A pairs with U

5. Base pairing creates the unique
secondary structure of transfer RNA
molecules.

6. Transcription
Transcription = production of RNA using DNA as a template
One DNA strand is used to produce a RNA strand, beginning at a promoter and ending at a terminator.
Base in DNA
template
Base in RNA product A U T G C

7. Structure of Transcribed Region

8. Transcription 3’---TACAAA GAGACT---5’ DNA template
Transcription requires
1. RNA polymerase, an enzyme that adds
nucleotides in a 5’3’ direction.
2. Nucleoside triphosphates
3. Energy: release of diphosphate
3’---TACAAA GAGACT---5’ DNA template
5’---ATGTTTCTCTGA---3’
Antisense strand
3’---TACAAAGAGACT---5’
5’---ATGTTTCTCTGA ---3’
5’---AUGUUUCUCUGA---3’ mRNA
Sense strand

9. Different Genes Can Have Different Template Strands
For each gene, only one of the two DNA strands is used as a template.

10. Applying Your Knowledge
What is the sequence of an RNA molecule transcribed from a DNA template strand that reads 3’-ATG-5’?
5’-TAC-3’
5’-CAU-3’
5’-AUG-3’
5’-UAC-3’
3’-TAC-5’

11. Stages of Transcription
Initiation
transcription apparatus binds to promoter
Elongation
RNA polymerase adds nucleotides to chain
Termination
recognition of termination signal
separation of RNA from DNA template

12. Features of the Prokaryotic Promoter

13. Two Forms of RNA Polymerase in Prokaryotes
Holoenzyme = Core enzyme Sigma factor Recognizes –10 and –35 regions
Binds to promoter Forms open promoter complex
Core enzyme continues transcription after initiation

14. Initiation Holoenzyme forms Holoenzyme binds to promoter
Open promoter complex forms
First RNA nucleotide binds

15. Elongation
RNA nucleotides are added in a 5’3’ direction by RNA polymerase core enzyme.

16. Rho-Dependent Termination
Rho-Dependent terminators have
region without secondary structure
sequence that produces a pause in transcription
Rho protein binds to region without secondary structure
Terminator sequences form hairpin to slow polymerase
Rho travels to terminator region and unwinds RNA-DNA duplex

17. Rho-Independent Termination
Rho-independent terminators have
inverted repeats
string of adenines
When terminator is transcribed
inverted repeats form hairpin that slows RNA polymerase
A-U pairs are unstable
RNA separates from template

18. Eukaryotic Transcription
Different types of RNA are produced by different polymerases.
Eukaryotic RNA Polymerase
Messenger RNA (mRNA)
RNA Polymerase II
Ribosomal RNA (rRNA)
RNA Polymerase I
Transfer RNA
(tRNA)
RNA Polymerase III

19. Features of the Eukaryotic RNA Polymerase II Promoter
General Transcription Factors + RNA Polymerase II bind to Core Promoter
Transcriptional Activator Proteins bind to the Regulatory Promoter

20. Initiation of Eukaryotic Polymerase II Transcription
Transcription Factor IID binds to TATA box on core promoter
Holoenzyme forms and binds to TFIID Holoenzyme = RNA Pol II + Transcription Factors
Basal Transcription Apparatus

21. Initiation of Eukaryotic Polymerase II Transcription
Basal Transcription Apparatus is needed to support minimal levels of transcription.
Transcription can be increased by Transcriptional Activator Proteins bound to
Regulatory Promoter
Enhancer Sequence

22. Termination of Eukaryotic Polymerase II Transcription
exonuclease
Termination of Eukaryotic Polymerase II Transcription
Polymerase II continues transcription beyond the coding region
Cleavage occurs at the 3’ end, near consensus sequence
Rat1 exonuclease binds to 5’ end and moves toward Polymerase II, degrading the RNA from 5’3’
Transcription terminates when Rat1 reaches Polymerase II

23. Transcription Termination for Eukaryotic RNA Polymerases I and III
RNA Polymerase I requires a termination factor that binds to a DNA sequence downstream of the termination site
RNA Polymerase III transcribes a terminator sequence to produce a region rich in uracil residues on the transcript
Pol I is similar to rho-dependent termination except that the terminator binds to DNA rather than RNA.
Pol III is similar to rho-independent termination except that a hairpin does not precede the string of uracils.

24. Applying Your Knowledge
Prokaryotes
Eukaryotes
Both Prokaryotes and Eukaryotes
Neither Prokaryotes nor Eukaryotes
Which organism(s) have
A. Sequences at –10 and –35 that are recognized by Holoenzyme?
B. Transcriptional Activator Proteins?
C. Rho-Dependent Termination?
D. Rat1 exonuclease activity?