The flow of genetic information occurs in all living cells

1
The Central Dogma
The flow of genetic information occurs in all
living cells from DNA to RNA
(transcription) from RNA to protein
(translation)
Figure 1
2
Transcription produces a single-stranded RNA
molecule complementary to the template strand of
the DNA
Transcription is catalyzed by a molecular
machine called RNA polymerase (RNAP)
Figure 2
3
Genes are transcribed
How does RNAP recognize genes?
Figure 3
4
Structure determines function

• ?Rpb2
• ? ? Rpb1

7 more eukaryotic subunits
All RNAPs are structurally similar the core
bacterial subunits are homologous and
structurally similar to the core eukaryotic
subunits
Figure 4
5
The minimal RNAP the bacterial model
Figure 5
6
Step 4. Once RNAP synthesizes about 10 nt of RNA,
sigma relaxes its grip, and RNAP undergoes a
series of conformational changes (which probably
includes a tightening of its jaws and the
placement of RNA in the exit channel.
Step 7. RNAP releases the DNA template and the
newly transcribed RNA.
Bacterial transcription cycle
7
Step 1a Forming the Active Polymerase
? ?
? ??
NT? dimer
HOLOENZYME (E?)
CT? dimer
? ?
?
? ??
NT? dimer
?
CORE ENZYME (E)

CT? dimer
?
?
SIGMA (?) specificity factor
Figure 7
8
Step 1b. Forming the TCC
? binds a DNA sequence called the Promoter
Figure 8
9
? gets help from the CT?
1
?
CT? dimer
CT? dimer
DNA
UP element
UP element CT? binding site
Figure 9
10
NOTE
1) downstream (3) double-stranded (DS) DNA 2)
unwound DNA (transcription bubble) with template
non-template strands
Figure 10
11
Step 4 promoter clearance the TEC
NOTE
3) DNARNA hybrid and the rudder that separates
DNA and RNA 4) Exit of RNA and rewound upstream
(5) DS DNA
Figure 11
12
Eukaryotic transcription Bacterial
transcription With the following exceptions
1. Core has 12 subunits vs 5
5. Promoter clearance requires modification of
core polymerase
Figure 12
13
Eukaryotic transcription
Figure 13
14
TFIIH (a helicase) unwinds DNA (not
shown) requires ATP similar to E?54 of
bacteria other bacterial E?s do not require ATP
TIC forms with addition of NTs abortive
transcripts formed, until
Phosphorylation of the CTD TIC morphs into TEC
TEC clears promoter leaving TF complex behind
TEC operates as in bacteria
Figure 14
15
Eukaryotic transcription Bacterial
transcription With a few exceptions
Eukaryotic DNA packaged by histones chromatin
tightly packed
Figure 15
16
Eukaryotic transcription Bacterial
transcription Several more exceptions
Prokaryotic transcripts often encode multiple
proteins - polycistronic Eukaryotic transcripts
typically encode a single protein - monocistronic
Eukaryotic transcripts are capped
polyadenylated Prokaryotic transcripts are not
Figure 16
17
Eukaryotic transcription Bacterial
transcription Several more exceptions
Eukaryotic transcripts must pass through the
nuclear membrane Prokaryotic transcripts do not
no nuclear membrane
Eukaryotic transcripts are spliced Prokaryotic
transcripts are not however, some are processed

Consequence
Eukaryotic transcription and translation are
uncoupled Prokaryotic transcription and
translation are coupled
Figure 17
18
Eukaryotic transcription Bacterial
transcription Several more exceptions