RNA Synthesis and Transcription in Bacteria Flashcards
Two parts of gene expression
- DNA –> RNA = TRANSCRIPTION
2.RNA –> protein = TRANSLATION
Pulse-chase method
Infecting nucleotides with radioactive components and traced in cells
Difference between RNA and DNA
RNA:
- thymine replaced by uracil
- ribose sugar instead of deoxyribose. Ribose has one more OH group
What form is RNA in?
A type. DNA IS B TYPE HELIX
Where does RNA synthesis take place on the strand?
between 3’ hydroxyl of one nucleotide and 5’ phosphate on adjacent one
mRNA
Messenger RNA produced by protein producing genes. Intermediate between DNA and protein. Only type of RNA that undergoes translation
What are the functional RNAs?
Transfer RNAs (tRNAs) and Ribosomal RNA (rRNA)
Which of the following RNA are involved in the process that leads to protein synthesis?
mRNA, tRNA, rRNA
How long is the transcription bubble of unwound DNA?
14 bp. ~8 RNA nucleotides paired with DNA inside transcription bubble
Transcription vs Replication?
Transcription:
- DNA-dependent RNA polymerases
- DNA unwinding is minimal
- Some regions copied at high levels; some low. Level of expression can be changed
How are bacterial genes expressed?
In groups called OPERONS consisting of genes relating to similar metabolic function
Where does RNA transcription begin?
Promoter upstream (5’)
Where does RNA transcription end?
Terminator region downstream (3’) from coding segment of gene
What catalyzes transcription in RNA?
RNA polymerase. Makes RNA from DNA but does not bind promoter or initiate RNA synthesis
Consensus sequences
Promoter– 5’ to 3’ coding strand sequence
E. coli promoter consensus sequence
TTGACA —17+/- 1 — TATAAT
Bacterial Transcription 4 steps
- promoter recognition
- transcription initiation
- chain elongation
- chain termination
What initiates transcription?
Holoenzyme that binds tightly to form CLOSED PROMOTER COMPLEX and unwinds 14 bp of DNA= OPEN PROMOTER COMPLEX. Holoenzyme initiates RNA synthesis at +1 site
What are the two transcription termination mechanisms in bacteria?
- Intrinsic termination
- Rho- dependent termination
What is intrinsic termination?
** most bacterial termination occurs this way
Inverted repeat sequences in transcript (6-8 uracil’s) fold into a stem loop structure called a hairpin. Hydrogen bonds break between A-U releasing transcript and terminating the process of transcription
What is Rho-dependent termination?
Rho protein binds to mRNA and brings separation of new mRNA and RNA polymerase. Rut site where Rho binds rich in cytosines. The Rho protein is activated by ATP
