Chapter 17: Gene Expression Flashcards
What carries out transcription?
RNA polymerase
Explain how RNA polymerase works in transcription.
- builds RNA 5’ —> 3’
- does not require a primer
Where does transcription begin?
at the 3’ of a promoter
What is a promoter?
short sequence of DNA where proteins bind to initiate transcription
Describe promoters in bacteria.
contain -35 box and -10 box
Describe promoters in eukaryotes.
promoters are variable
What are transcription factors?
proteins that bind to DNA and are involved in the process of transcription
What are the transition factors in bacteria?
sigma factors
Describe sigma factors.
- primary is sigma 70
- detachable subunit of RNA polymerase
Describe the binding of sigma factors.
- sigma looks for a specific site on the promoter
- binds first to DNA (-10/-35 boxes), then guides the RNAP to where transcription will begin
What happens to sigma when transcription begins?
detaches from the core enzyme, then the core enzyme continues transcribing
Describe the RNAP holoenzyme.
- only in bacteria
- means “whole enzyme” (holo=whole)
- is a sigma + core enzyme
What are the 3 overall steps of transcription?
- initiation
- elongation
- termination
What is the initiation step of transcription?
- RNAP binds to sigma, sigma binds to promoter
- RNAP opens DNA to begin transcription
- sigma released, which allows RNAP to continue transcribing
What is the elongation step of transcription?
- RNAP continues transcribing
- RNAP moves along DNA continuously
What is the termination step of transcription?
- a termination signal is transcribed from RNAP and folds into hairpin
- hairpin causes the release of RNA from RNAP
- THINK HAIRPIN=TERMINATOR
- at dance, hairpin hurt head SO BAD, so you terminate it and causes a release of hair
What are some differences between eukaryotic transcription and bacterial transcription?
- euks have 3 RNA polymerases (one for each type of rna), proks have 1
- euks have diverse promoters
- euks=general transcription factors (and mu;tiple required for initiation of transcription); proks=sigma
- euks have multiple methods of termination (poly(A) signal)
- euks= separate transcription and translation
What is the poly (A) signal?
termination downstream of a long stretch of A nucleotides
Describe RNA processing in eukaryotes.
DNA –> pre-mRNA –> mature mRNA
DNA to pre-mRNA = transcription
pre-mRNA to mature mRNA = RNA processing
What are exons?
genes that remain part of mRNA (EXons=EXpressed)
What are introns?
sections removed from mRNA (INtrons=INtervene)
Describe the 3 steps of RNA processing (splicing).
- snRNPs assemble, then bind the the pre-mRNA
- snRNPs assemble to form the spliceosome
- the intron is cut out/removed as a ‘lariat’ structure (snRNAs/ribozymes perform the cleavage)
What are the cap and tail in RNA processing?
cap: 5’ cap (modified GTP added to 5’ end)
tail: poly (A) tail (long chain of As added to 3’ end)
What are the functions of having a cap and tail in RNA processing?
- enables ribosome to bind to the mRNA
- protects mRNA from degradation by ribonucleases (RNases)
