Bacteril transcription (L11) Flashcards
(24 cards)
What is the ‘antisense’ strand
the Template strand used in transcription.
What bases does RNA use
Adenine, cytosine, guanine and Uracil instead of Thymine
Why is Uracil not in DNA
Cytosine undergoes spontaneous deamination, which produces Uracil, but enzyme uracil-DNA glycosylase removes the Uracil in DNA, and is repaired by DNA polymerases.
What are the three major classes of bacterial RNA
mRNA, tRNA, rRNA
what is mRNA
messenger RNA, codes for proteins
What is tRNA?
transfer RNA, used to match codon to its complementary amino acid in protein synthesis.
What is rRNA?
ribosomal RNA, constituents of ribosomes, used in protein synthesis.
What is the gene being transcripted called?
An operon
Name all parts of an operon, downstream.
promoter region, which includes the operator region, protein coding sequences, terminator sequence.
What is the role of the promoter region in an operon.
it is the binding site for RNA Polymerase
what is the role for the operator region?
binding site for transcription factors. determines whether the gene is expressed depending on conditions. (‘on/off’ switch)
What is the function of the terminator sequence.
transcription ends here.
what does polycistronic mean?
multiple genes, in this context the operon is polycistronic, as it contains multiple protein coding sequences.
What is the STRUCTURAL difference between core RNA Polymerase and the holoenzyme RNA Polymerase
holoenzyme includes a sigma subunit - in addition to alpha, beta, omega subunits
What is the difference in function between the core and holoenzyme RNA Polymerase.
holoenzyme RNA Polymerase is essential to bind to the promoter region. core RNA Pol is non specific but allows for transcription as it is not bound to the promoter region.I
What was the method to identify the promoter region
addition of small amount of DNase to create ‘ nicks’ in DNA, and in an electropherisis, will display fragments, DNase will not ‘nick’ where the RNA Pol sits, showing a ‘footprint’ of protected sequence i.e the promoter region. There are two protected regions
why are there two protected areas during the promoter region test
because the sigma unit in holoenzyme RNA Pol has 2 contact points.
Where are the protected sequences on the operon.
-10bp and -35bp
What are the 3 stages of transcription
Initiation, elongation, termination
What is the inititation stage of transcription
core RNA polymerase binds to DNA non-specifically
sigma unit then binds to the core polymerase, which allows it to bind to the specific promoter region based on WHICH sigma subunit was bound to the core enzyme.
RNA pol pulls downstream dna towards itself, scrunching the DNA (i.e ‘abortive initiation’) until bound to the promotor region and DNA opens at -10bp, promotor sequence is now OPEN.
this causes NEGATIVE supercoiling upstream, POSITIVE supercoiling downstream, which topoisomerases deal with
the sigma subunit detatches after about 10 or 15 nucleotides have been synthesised.
What is the elongation stage?
the synthesis of the new RNA .
What is the termination stage?
there are two mechanism:
p-independent and p dependant
independant- terminatior sequence in the RNA is recognised. common sequence is palindromic GC rich sequence followed by T rich sequence, which when transcripted will form a hair pin, causing the RNA Pol to dissociate.
dependent- p protein is required to break the RNA:DNA duplex in the transcription bubble. protein binds to the RNA strand and chases RNA pol and disrupts it causing dissociation.
