Transcription Flashcards
What is Transcription
DNA is copied into RNA by the enzyme RNA polymerase
Reverse transcriptase
make DNA from RNA template
Most eukaryotic genes contain noncoding sequences among the
coding regions
alternative splicing
Coding sequences can be read in various combinations, each coding for a unique polypeptide chain;
Three characteristics of the Genetic Code?
Degenerate, Non-overlapping and Unambiguous -
Who provided the triplet nature of the code?
Francis Crick & Sydney Brenner (1961)
Open reading frame(ORF) can cause?
Frameshift mutations
a way of dividing thesequence of nucleotidesin anucleic acid(DNAorRNA) molecule into a set of consecutive, non-overlapping triplets.
Reading frame
amino acids/ stop signals are called
codons
Open reading frame(ORF) contains?
no stop codons
Causes Garbled words due to changes in reading frame
Due to Frameshift mutation
Transcription of mRNA from DNA does same thing but uses
uracil (U) in place of thymine
Transcription of mRNA from DNA uses what four stages
Binding, Initiation, Elongation and Termination
Sigma factors promotes
binding of RNA polymerase to specific DNA sequences called promoters
RNA polymerase in bacterial cells ONLY has
single kind of RNA polymerase and a lot of α and β subunits and sigma factor
RNA synthesis takes place when the DNA is
unwound
RNA polymerase catalyzes the formation of a
phosphodiester bond between the NTPs
Is transcription in Prokaryotes or Eukaryotes more complex?
Eukaryotes
Uses 3 different RNA polymerases
Transcription in Eukaryotes
a deadly toxin produced by the mushroom, Amanita phalloides an inhibitor of RNA polymerase
α-aminitin
Small nuclear ribonucleic acid(snRNA) AKA
U-RNA, all RNA molecules that are found within the nucleus ofeukaryoticcells.
processing of pre-mRNA in the nucleus
U-RNA
a smallnon-coding RNAmolecule
Functions in transcriptional and post-transcriptionalregulation of gene expression
miRNA
What are the three classes promotors of Eukaryotes
RNA polymerase I
RNA polymerase II
RNA polymerase III
Consists of core promoter and upstream control element
RNA polymerase binds to the core promoter
RNA polymerase I
Which RNA Polymerase uses At least 4 DNA sequences are involved
RNA polymerases II
Used to make mRNA in RNA polymerase II
BRE, TATA box, Inr and DPE
Common upstream control elements
CAAT and GC box
upstream control elements:
Those within 100–200 nucleotides of the startpoint are called
proximal control elements
upstream control elements:
Those farther away from 100–200 nucleotides of the startpoint
enhancer elements
Entirely downstream of the startpoint - for transcribing tRNA and 5S-rRNA
RNA Polymerase III
Required to bind to its promoter and initiate RNA synthesis
General Transcription Factor
What plays a crucial role in binding stage of eukaryotic transcription
protein-protein interactions
General transcription factors in binding RNA polymerase II to DNA:
what binds to what
- TFIID first binds to TATA box in the DNA sequence
- Preinitiation complex binds to promoter region
- General transcription factor TFIIH
possesses both helicase activity, that unwinds DNA, and a protein kinase activity that catalyzes the phosphorylation of RNA polymerase II
General transcription factor TFIIH
changes the shape of RNA polymerase II, so it can initiate RNA synthesis at the startpoint
Phosphorylation
Helicase activity
unwind the DNA, so that RNA polymerase molecule can begin to move
Ability to recognize and bind to DNA promoter sequences is conferred by one of its subunits
TFIID
If there is a DNA damage, RNA polymerase becomes
stalled temporarily during DNA excision repair
RNA polymerase I: Termination signals
Terminated by a protein factor that recognizes an 18-nt termination signal in the growing RNA chain
RNA polymerase II: Termination signals
Termination signals include a short run of U’s and no proteins are required for their recognition
RNA polymerase II: Termination signals
mRNAs are cleaved at a specific site, a cleavage site, before transcription is actually terminated
The cleavage site is10-35 nts downstream from a special AAUAAA sequence in the growing RNA chain
Newly produced RNA molecule
primary transcript
all chemical modifications necessary to generate a final protein product from the primary transcript
RNA processing
RNA processing uses what three RNA’s
rRNA, tRNA and mRNA
most abundant and most stable RNA in cells and In eukaryotes, cytoplasmic ribosomes contain four types?
rRNA
The Presence of three different rRNA genes within a single transcription unit ensures what?
Theres RNAs in equal amounts
The nontranscribed spacers
separate transcript units within each cluster
transcribed spacers
The DNA sequences that code for the three rRNA
remove the transcribed spacers and release the mature rRNAs
Cleavage reactions
i) Removal of leader sequence at the 5’ end
ii) Replacement of two nucleotides at the 3’ end by the sequence CCA
iii) Chemical modification of certain bases
iv) Excision of an intron
tRNA gene into mature tRNA (clover structure)
Which RNA does not require processing before translated?
Bacteria RNA
transcription and translation occur simultaneously
In what Eukaryotes or Prokaryotes is Transcription and translation are separated, both time and space
Eukaryotes
Transcription takes place in
the nucleus
Translation takes place in
in cytoplasm
What are the three processes of mRNA
- Capping
- poly (A) tail
- Splicing
