Unit 9: Eukaryotic Transcription Flashcards
What are the differences between prokaryotic and eukaryotic transcription?
1) bacterial transcription occurs on a DNA template and in eukaryotes transcription occurs on chromatin
2) in prokaryotes RNA pol can scan the DNA to find and bind to the promoter. Inn Eukaryotes RNA polymerase cannot read the DNA and instead uses transcription factors that must bind to the DNA at specific sites before the RNA polymerase can bind
What is chromatin? What is chromatins main component?
-The DNA in eukaryotes that is associated w/proteins. this DNA + protein form chromatin and the primary components of chromatic are histones
What are histones?
-proteins that compact the DNA
What must happen to the chromatin in eukaryotes in order for the RNA polymerase to bind to the promoter?
-the chromatin must be opened
Why are transcription factors needed for eukaryotic transcription but not prokaryotic?
-b/c prokaryotic RNAs cannot read the DNA w/o transcription factors
What do the basal transcription factors form? Why are these transcription factors needed?
-they form the initiation complex at the promoter region. These factors are needed for initiation and bind to DNA, allowing RNA polymerase to bind to the transcription factors of DNA complex with the core promoter
TRUE OR FALSE: Elongation in eukaryotes always need basal transcription factors
FALSE: these factors are needed for initiation but most are not needed for elongation
What is a core promoter?
-The shortest sequence at which an RNA polymerase can initiate transcription
What is the core promoter for RNA polymerase II?
-it is the minimal sequence at which the basal transcription apparatus can assemble, and it includes three sequence elements: The Inr, the TATA box, and the DPE (downstream promoter element)
What are the three sequence elements of the core promoter?
1) the Inr (initiator)
2) the TATA box
3) the DPE (downstream promoter element)
What forms the basal transcription apparatus?
-the basal factors (initiation complex) joined to the RNA polymerase forms the basal transcription apparatus.
What is an enhacer?
-a cis-acting sequence that increases the utilization of most eukaryotic promoters and can function in either orientation and in any location (up or downstream) relative to the promoter
what is a silencer?
-a short sequence of DNA that can inactivate expression of genes in its vicinity (this is an example of negative regulation)
What are housekeeping genes?
genes that are constitutively expressed in all cells b/c they provide basic functions needed for sustenance/survival of all cell types
What is a coactivator?
-factors required for transcription that do not bind DNA, but are required for DNA-binding activators to interact w/the basal transcription factos
What does RNA polymerase I synthesize?
-RNA pol I synthesizes ribosomal RNA (rRNA) in the nucleolus
What does RNA polymerase II synthesize?
- it synthesizes messenger RNA (mRNA) in the nucleoplasm and a few small RNAs
- it is also responsible for heterogenous nuclear RNA (hnRNA), which is a precursor for most of the mRNA
What is heterogenous nuclear RNA (hnRNA)?
-RNA that consists of transcripts of nuclear genes made primarily by RNA pol II; it has a wide size distribution and variable stability
What does polymerase III synthesize?
- it transcribes transfer RNA (tRNA), ribosomal RNA (rRNA), and some small RNAs in the nucleoplasm
TRUE OR FALSE: Some subunits are common to all three eukaryotic RNA polymerase?
TRUE; like TBP (TATA binding protein)
WHat is the largest subunit in RNA polymerase II?
-Carboxy-terminal domain or CTD, which consists of multiple repeats of a heptamer/heptapetide (multiple consesus sequence of seven amino acids)
TRUE OR FALSE: The two largest subunits in eukaryotic polymerase are homologous to the beta and beta prime subunit of the bacteria RNA polymerase
TRUE
Is there a homologous subunit in eukaryotic RNA polymerase that is similar to the sigma factor in prokaryotes?
-no b/c the function of the sigma factor is taken over by the basal transcription factors
What is CTD? What is the role of CTD?
- carboxy terminal domain that consists of multiple repeats of a consensus sequence of 7 amino acids or heptapeptides (deletion of more than half of these repeats can be lethal)
- CTD is phosphorylated at several serine and threonine residues and it is involved in regulating the initiation process, elongation, mRNA processing, and transport of mRNA into the cytoplasm.