8. Transcription and processing in prokaryotes Flashcards
The central dogma
Flow of genetic info from DNA to RNA (transcription) to proteins (translation)
RNA self-replication
RNA- dependent RNA polymerase activity in RNA viruses
RNA can be retrotranscribed to DNA
Retrotranscriptase activity in retroviruses
Protein + infection
= prion
E.g., self-reproducing pathogenic proteins
Primary function of DNA
Store genetic info.
Primary function of RNA
Transducer DNA messages into protein
Primary functions of proteins
Read info. And catalyze reactions as ribosozymes
Transcription and translation in prokaryote vs eukaryotes
Prokaryotes can’t regulate RNA and protein synthesis
In eukaryotes nucleus divided transcription and translation=greater control of RNA and protein synthesis
RNA molecules involved in transcription
MRNA SnRNA TRNA RRNA MiRNA
RNA polymerase
Highly conserved proteins (so function stays same)
Steps for DNA info transmission to protein:
- Gene expression
- MRNA processing
- MRNA transport
- MRNA translation
Spiegelman’s experiments
Rapid switch from transcription of E.coli genes to phage genes;
phage hijacks cells transcription machinery, but cells then actively destroy messenger
Pulse-chase labeling experiments
Prove RNA synthesized in nucleus and then transported to cytoplasm
RNA ribonucleotides
- Adenosine
- Guanosine
- Cytidine
- Uridine
RNA vs. DNA
1. Single vs. double More options for shape 2. OH groups in position 2 3. Uracil pairs with A during transcription pairs with A or G when folding 4. RNA can catalyze reactions
Ribozymes
Catalytic RNA
mRNA
Messenger RNA
Intermediates that carry genetic info from DNA to ribosomes
snRNA
Small nuclear DNA
Structural components of spliceosomes
tRNA
Transfer RNA
Adaptors between amino acids and codons in mRNA’s
rRNA
Ribosomal RNA
Structural and catalytic components of ribosomes
miRNA
MicroRNA
Short, single-stranded RNA’s that block expression of complementary mRNAs
Differences between DNA and RNA
Precursors are ribonucleic triphosphate (not deoxy)
Only 1 strand of DNA as template (thus, only 1 direction 5 prime-3 prime)
RNA chains can be initiated de novo (no primer)
Uracil instead of thymine
Antisense strand
DNA template strand (complementary to RNA)
Sense strand
DNA nontemplate ‘coding’ strand
Identical to RNA molecule (except U & T)
RNA synthesis is catalyze by…
RNA polymerases
Phosphodiester bond
Free nucleotide triphosphate bonds to hydroxyl strand
Sense (+) RNA
RNA product from template strand is complementary
Transcription bubble
Region in molecule where strand opens up to allow polymerase
Stages of transcription
- RNA chain initiation (polymerase)
- RNA chain elongation
- RNA chain termination (nascent RNA molecule)
Holoenzyme
Initiation of transcription (released after)
Sigma factor
Initiation of transcription (released after)
Stages of initiation (prokaryote)
A)RNA polymerase binds to promoter (via holoenzyme)
Formation of phosphodiester bonds between 1st few ribonucleotides
B) initiation signaled by sigma removal
+1 site
Where transcription starts (between promoter and ATG)
UTR
Untranslated RNA; untranslatable regions of RNA transcript
5’ UTR before AUG & 3’ UTR after stop codon
Termination signals
Rho dependent
Rho independent
Rho-dependent terminators
Require protein factor
Stop codons in mRNA triggers release of attached ribosomes (leaves room for rho to bind)
Rho migrates on RNA and reaches polymerase at the transcription bubble
Rho-independent terminators
Do not require protein factor
G-C rich stemloop structure upstream of poly-U sequence
Polymerase pauses, backtracks, proceeds, and encounters stem loop
Encourages disassociation of RNA and RNA polymerase—> transcript released
