Transcription 1&2 (Week 5) Flashcards
What does the role of RNA entail?
RNAs play a vital role in using that information to produce proteins.
Is RNA a linear or double stranded?
Linear Polymer
Is RNA ribose or deoxyribose based?
Ribose
What base replaces thymine in RNA?
Uracil
How is RNA copied from DNA?
The sequence of the RNA molecule is the complement of the TEMPLATE strand (3’-5’ )
The sequence of the RNA molecule is the same as the CODING strand (5’-3’ )
T in DNA is replaced by U in RNA
Can both strands of DNA act as templates or only one?
Both
How is RNAs ability to adapt to a secondary structure Important?
The ability to form complex secondary structures is important for tRNAs and rRNAs
List the major types of RNA in prokaryotes?
Ribosomal RNA (rRNA) Transfer RNA (tRNA) Messenger RNA (mRNA)
List the principle types of RNA produced in cells and their function?
mRNA - code for proteins
rRNA - form the basic structure of the ribosome and catalyse protein synthesis
tRNA - central to protein synthesis as adaptors between mRNA and amino acids
snRNA (small nuclear RNA) - function in a variety of nuclear processes including the splicing of pre-mRNA
snoRNA (small nucleolar RNA) - helps to process and chemically modify rRNAs
miRNA (microRNA) - regulate gene expression by blocking translation of specific mRNA and cause their degradation
siRNA (small interfering RNA) - turn off gene expression by directing the degredation of selective mRNAs and the establishment of compact chromatin structures
piRNA (piwi-interacting RNA) - bind to piwi proteins and protect the germ line from transposable elements
lncRNA (long non-coding RNA) - many of which serve as a scaffolds; they regulate diverse cell processes, including X-Chromosome inactivation.
What do Prokaryotic RNA polymerases consist of?
Prokaryotic RNA polymerase has 5 subunits, 4 make up the core polymerase and 1, the sigma factor, is required for initiation
What signals the start of transcription in prokaryotes?
the consensus sequences (ideal promoter sequences) -35 and -10 signal the start of transcription
What does the Haloenzyme do, during initiation? (1)
Holoenzyme (core polymerase + sigma factor) assembles
and locates a promoter
How does the process of elongation occur?
As polymerase moves along the template, sigma factor loses contact with the promoter.
Sigma factor is released, freeing the polymerase to progress rapidly along the template (~ 50 bases/sec)
How does the process of termination occur?
Termination signal coded in the DNA causes the formation of a hairpin loop in the RNA. This destabilises the polymerase’s hold on the RNA.
The completed RNA is released by the polymerase. The cycle can now begin again.
What does RNA polymerase I consist of?
RNA polymerase I - 5.8S, 18S, and 28S rRNA genes
List the role that TFIID subunits play in transcription?
TBP (subunit); Recognises TATA box (1 subunit)
TAF (subunit); Recognises other DNA sequences near the transcription start point; regulates DNA binding by TBP (11 subunits)
How does the initiation of transcription occur in eukaryotic cells?
Tata binding protein(part of TFIID) binds to the TATA box.
Conformational change in the DNA allows binding of TFIIB
How does TATA binding change the topography of the DNA?
TBP binds to the TATA box and induces a bend in the DNA helix
This may serve as a “landmark” to attract the other general transcription factors