BIO 205 TRANSCRIPTION Flashcards
what is transcription
- RNA synthesis
* creating of single-stranded molecule on way to being translated into functional model
where does transcription occur in prokaryotes
cytoplasm SAME TIME AS TRANSLATION
where does transcription occur in eukaryotes
nucleus
RNA diff from DNA
- uses uracil not thymine (U-A)
* single-stranded
RNAs can form secondary structures via ___
intramolecular interactions
types of RNA in eukaryotes
major- mRNA: intermediate transient products (short time)
rRNAs, tRNAs, and snRNAs : final products
mRNA stands for
messenger RNA
rRNA stands for
ribosomal RNA
tRNA stands for
transfer RNA
snRNAs stands for
small nuclear RNA
All eukaryotic RNAs are created by
3 types of RNA Polymerases
DNA polymerase and RNA polymerase differ?
DNA polymerase
• synthesizes a DNA strand
• used in DNA replication
• faster
RNA polymerase
• transcription to synthesize the mRNA strand (not H-bonded to the DNA template)
• doesn’t need primer
• no proofreading
• 10x slower
• not all regions of DNA transcribed, only coding region
properties of RNA Polymerase
- uses ribonucleoside triphosphates (ATP, CTP, GTP, UTP) and Mg++
- 5’ –> 3’ phosphodiester bonds
- needs template DNA strand
- RNA is complementary to template
RNA polymerase transcribing for how long
short time
coding strand also called
sense strand
template strand also called
antisense strand
coding strand …
specifics amino acid sequence of protein
template strand …
where RNA is actually transcribed
coding and template formation:
asymmetric transcription
mRNA: 5’ —–> 3’
template: 3’ 3’
gene regions controlling transcription
- PROMOTER : “upstream” - 5’ controlling region
2. TERMINATOR : “downstream” - 3’ controlling region
prokaryotic promotor
- promoter: a key point of regulation for transcription
- consensus sequences (can change slightly)
- provide binding site for RNA polymerase
prokaryotic promotor elements
TATA BOX/Pribnow box @ -10
-35 box
prok. TATA BOX aka:
Pribnow box
prok. TATA BOX is where?
-10
prokaryotic promoter numbers
-10, -35
consensus analysis
can change very slightly
• defines target regions
“Wreck and Check”
1- mutate specific region
2- check if transcription affected
why does mutation work better than wild type
- promoter is never turned on all the way
* only need enough to repair
eukaryotic promoter numbers
-25, -75
euk. TATA box aka:
Hogness box
euk. TATA box is where?
-25
structure of E. coli RNA Polymerase
• core enzyme consists of 5 subunits
Core Enzyme + Sigma Factor
= HOLOENZYME
3 phases of transcription
initiation, elongation, termination
differences between prokaryotic and eukaryotic polymerase binding
- prokaryotic RNA Polymerase binds to the DNA template directly
- eukaryotic RNA Polymerase requires co-factors
transcription of Prokaryotes
- Initiation: RNA polymerase recognizes promoter; starts the transcription
- Elongation: RNA strand continuously grows
- Termination: RNA polymerase stops synthesis and nascent RNA separates from DNA template
Initiation in Prokaryotes
- no primer for RNA synthesis
- sigma factor associates with core enzyme (HOLOENZYME) and begins searching for promoter
- finds promoter, binds between -10 and -35 (ALL)
- sigma factor falls of RNA pol. when first phosphodiester bond is formed
- core enzyme moves along for elongation
Eukaryotic Transcription Initiation
• needs many transcription factor proteins
how much does RNA Polymerase unwind
17 base pairs, doesn’t need ATP
transcription: ELONGATION
- can be transcribed simultaneously from the same segment of DNA
- core enzyme slides on the DNA template toward the 3’ end
- Free NTPs added sequentially to the 3’-OH of the nascent RNA strand
elongation - release of the Sigma factor causes…
• conformational change to core enzyme
NTP
nucleoside triphosphate
RNA Polymerase Enzyme
- One core enzyme complex synthesizes the whole RNA chain (it is 100% processive)
- RNA polymerase has no editing activity – more error-prone
Termination
Prok.
- RNA polymerase stops moving on DNA template
- RNA transcript falls off transcription complex
• occurs in either: Rho-dependent or Rho-independent
Rho-INDependent
versus
Rho-Dependent
- INDEPENDENT: RNA forms a hairpin loop, causes RNA polymerase to pause, allowing Rho protein to catch up, and displace RNA polymerase from the template – STOPPING transcription
- DEPENDENT: rho protein disassociates the RNA Polymerase and moves it off of template
Inhibitors of Transcription
- Rifamycin B:
- Actinomycin D:
- a-Amanitin: (poisonous mushrooms)
what is Rifampin used to treat
TB, leprosy, meningitis
Rifamycin B:
inhibitor of prokaryotic transcription
(not eukaryotes)
– an antibiotic [Rifampin]
- stops chain elongation after first phosphodiester bonds formed
- remains bound to the promoter, blocking other enzymes
transcription and replication
Actinomycin D:
elongation inhibitor for both euk and prok – binds tightly to duplex DNA, inhibiting transcription and replication
a-Amanitin
(poisonous mushrooms)
- forms tight complex w eukaryotic RNA pol II and lose complex w RNA pol III
- blocks elongation steps in eukaryotes
• RNA polymerase I, mitochondrial, & prokaryotic RNA polymerases are insensitive to a-amanitin
Eukaryotic Promoter Elements
TATA Box
CAAT Box
GC Elements
CAAT Box
eukaroytic @ -75
Eukaryotic transcription factors
• TBP = TATA-Binding
Protein
• is part of TFIID = Transcription factor II D
• Involves many transcription factor proteins instead of just sigma factor
(eukaryotic) Enhancer
(on strand) binding site for activator protein
