Topic 3: Transcription Flashcards
Do all cells have the same genomic DNA?
yes
If all cells have the same genomic DNA, how are there so many different types of cells?
Because different cells express different genes making them different.
In which direction are mRNA molecules made?
5’ to 3’ direction
Describe the bacterial RNA polymerase. What is the significance of the sigma subunit?
RNA polymerase catalyze the growth of an RNA chain in 5’ to 3’ direction. Sigma subunit positions RNA polymerase at the site of transcription initiation.
Why are the -10 and -35 elements important?
DNA sequence that RNA binds in order to initiate transcription. Where the sigma subunit binds to. Genes with elements that differ from the consensus are transcribed less efficiently than closer ones.
How does initiation of transcription happen in bacterial cells?
Sigma factor guides RNA polymerase to the promoter by binding to 10 and 35 consensus sequence. RNA polymerase unwinds parts of the DNA. RNA polymerase joins two free nucleotides together. After 10 nucleotides are joined the sigma factor leaves the polymerase and RNA polymerase continues to elongate the growing RNA chain.
How does elongation of transcription happen in bacterial cells?
RNA polymerase continues to unwind the DNA in the 3’ direction while unwinding in the 5’ direction.
How does termination of transcription happen in bacterial cells?
Elongation continues until RNA polymerase hits a termination signal. RNA formed from the transcription of termination site will from a stable stem looped structure through base pairing. After transcription of residues, the RNA is released from RNA polymerase and RNA polymerase will then dissociate from the DNA template.
How many polymerase prokaryotes have? How many does eukaryotes have?
prokaryotes = 5
Eukaryotes = 5
What is the TATA box?
Promoter region on eukaryote DNA where transcription factor binds to
What is the transcription factor? How are they different from gene-specific transcription factors?
finds eukaryotic promoters to initiate transcription. Work in gene gene-specific manner is gene specific transcription factors. Needed for transcription of all genes, is general transcription factors.
How is initiation of transcription different eukaryotes?
General transcription factor binds to the promoter. The binding recruits a second general transcription factor. RNA polymerase II binds to this complex with a third factor. Two more factors are added forming the “pre initiation complex”
What is the preinitiation complex and why is it important?
After RNA polymerase II binds to this complex with third factor, two more factors are added forming the “pre initiation complex” stimulates transcription
What are the three modifications done to pre-mRNA and why are they important?
5’ cap = Helps mRNA to be exported. Prevents degradation of mRNA. Assist ribosomal binding during translation.
Poly A tail = prevents degradation of mRNA. Helps regulate translation
RNA splicing: removes introns and joins exons creating an mRNA molecule with a continuous coding sequence.
What would be the consequence of not having splicesomes?
Without spliceosome introns will not be spliced out and will be part of the coding sequence. Also provided a mechanism for tissue specific and developmental regulation of gene expression.
Regulation of gene expression
Behavior of cells determine not just by what genes are inherited but by what genes are expressed at certain times
Bacterial promoter
DNA sequence that RNA polymerase binds in order to initiate transcription
Closed promoter complex
When sigma factor guides RNA polymerase to the promoter by binding to the -10 and -35 regions
Open promoter complex
RNA polymerase unwinds 12-14 bp of the DNA
Termination signal
Signal tells RNA polymerase to release RNA, RNA polymerase will then dissociate from the DNA template
Messenger RNA (mRNA)
Associated with protein coding genes
Ribosomal RNA (rRNA) and Transfer RNA (tRNA)
Associated with RNA processing, translation and protein transport
RNA polymerase II
transcribes protein coding genes to yield mRNA
Promoter elements
Where general transcription factors bind to
