CHAPTER 12 Flashcards
(39 cards)
What is transcription in genetics?
Transcription is copying a DNA sequence into an RNA sequence, the first gene expression level.
What sequences define the beginning and end of a gene and regulate RNA synthesis?
DNA base sequences define the beginning and end of a gene and regulate RNA synthesis.
What is a promoter in gene transcription?
A promoter is a DNA sequence that promotes gene expression by directing the initiation of transcription. It is typically located upstream of the transcription start site.
What are the three stages of transcription?
- Initiation
- Elongation
- Termination
During transcription initiation, what happens at the promoter?
RNA polymerase binds to the promoter with the help of transcription factors, forming the open complex where DNA unwinds.
What happens during the elongation stage of transcription?
RNA polymerase slides along the DNA in the open complex to synthesize RNA, using the template strand in a 3’ to 5’ direction.
What is the role of sigma factor in bacterial transcription initiation?
Recognizes the -35 and -10 sequences in the promoter, facilitating the binding of RNA polymerase to the DNA.
Describe rho-dependent termination in bacterial transcription.
Rho-dependent termination requires the rho protein, which binds to the RNA and moves toward the RNA polymerase to release the transcript.
What is rho-independent termination?
Rho-independent termination involves a uracil-rich sequence and a stem-loop structure that causes RNA polymerase to dissociate from the DNA.
What is a consensus sequence in a promoter?
The most common promoter sequence results in high transcription levels; sequences deviating from it usually result in lower transcription.
Name the three types of eukaryotic RNA polymerases and their functions.
- RNA pol I: transcribes rRNA genes (except 5S rRNA)
- RNA pol II: transcribes protein-coding genes (mRNAs)
- RNA pol III: transcribes tRNA and 5S rRNA genes
What is the function of enhancers and silencers in transcription regulation?
Enhancers increase the transcription rate, while silencers decrease it; both regulatory elements affect RNA polymerase binding.
What is the role of general transcription factors in eukaryotic transcription?
-Assist RNA polymerase II in binding to the promoter
-Essential for the formation of the transcription initiation complex.
How does the allosteric model explain RNA polymerase II termination?
It suggests that RNA polymerase II destabilizes and dissociates from the DNA after passing the polyA signal.
RNA splicing
Removing introns from pre-mRNA and joining exons to produce a mature mRNA.
What modifications occur to eukaryotic pre-mRNA?
- Addition of a 5’ cap
- Polyadenylation (3’ polyA tail)
- Splicing to remove introns
How are tRNA precursors processed?
tRNA precursors are cleaved at the 5’ and 3’ ends by exonucleases and endonucleases to produce mature tRNA.
What is a ribozyme?
It is an RNA molecule with catalytic activity, such as RNaseP, which cleaves precursor tRNA.
RNaseP (endonuclease)
Enzyme creates the correct 5’ end of tRNA
What happens at the 3’ end of tRNA during processing?
A different endonuclease cuts the 3’ end, and RNaseD (exonuclease) removes 9 nucleotides from the 3’ end.
tRNA nucleotidyltransferase
Enzyme adds CCA to the 3’ end of tRNA
What are the three main splicing mechanisms?
- Group I intron splicing
- Group II intron splicing
- Spliceosome-mediated splicing.
What is a common result in all splicing mechanisms?
Removal of the intron and covalent linkage of exon fragments.
What is self-splicing, and which groups does it include?
Splicing that occurs without enzymes, by the RNA itself; includes Group I and Group II introns.
