Chapter 13 pt.2 Flashcards
What are the 4 types of RNA polymerases in humans?
RNA poly I
RNA poly II
RNA poly III
Mitochondrial RN poly
What does RNA poly I transcribe and where?
some rRNA (ribosomal RNA)
In nucleolus
What does RNA poly II transcribe and where?
mRNA, (messenger RNA), miRNA (microRNA), snRNA (small nuclear RNAs)
In nucleoplasm
What does RNA poly III transcribe and where?
tRNAs (transferRNA), rRNA (ribosomal RNA)
In nucleoplasm
Define nucleoplasm
Any region besides the nucleolus
How many subunits does RNA Poly II have?
12 subunits
What is transcription (eukaryotic) controlled by?
Promoters, enhancers, and silencers
Define promoters (eukaryotic)
Lie just ahead of the gene and binds RNA polymerase and transcription factors. A few dozen base pairs long, before/near the transcription start site (TSS)
Define transcription factors
Proteins that recruit RNA polymerase to begin transcription
Define general transcription factors
TFs used at every gene and are essential.
Define activators
Type of TF that increases transcription
Define repressors
Type of TF that decreases transcription
Define enhancers
DNA sequence located far from the gene and increases transcription
Define silencers
DNA sequence located far from the gene and reduced transcription
How do enhancers/silencers function?
They are found kilobases from the target promoter, with TFs bound to them. The DNA loops around so that they have contact with the promoter, allowing these TFs to either increase or decrease transcription initiation for the target gene.
How does elongation and termination occur (eukaryotic)?
- Termination begins with transcription of polyadenylation signal
- Various proteins then bind, cut, and release the RNA
- RNA goes to be processed
Define polyadenylation signal
DNA sequence that signals the end of the gene - is transcribed.
What is the new, unprocessed RNA molecule called?
precursor mRNA (pre-mRNA)
What does pre-mRNA undergo?
Maturation process called processing
What are the 4 maturation processes?
- Addition of 5’ cap
- Splicing
- Polyadenylation
- Post-transcriptional modifications
What is the addition of the 5’ cap?
An inverted, methylated guanosin protects RNA from degradation
Define splicing
Removing and rejoining pieces of RNA. Removes introns and rejoins the exons.
Define introns
Regions that do NOT code for the protein and are removed during splicing. Average human gene has ~9 introns
What is the importance of introns?
Allows for alternative splicing,
may have functional DNA elements (such as being an enhancer or silencer for another gene)
or other RNA derivatives (when removed, may function as a different type of RNA)
Define alternative splicing
Exons are combined in different orders to produce different proteins.
Define exons
Regions that DO code for the protein and are spliced back together
Define spliceosome
RNA-protein complex that conducts splicing
What is a spliceosome made up of?
snRNAs
Ribozyme
What does an snRNA do?
Recognizes splicing sites in introns
What does the ribozyme do?
Catalyzes the splicing reaction
Define polyadenylation
A series of adenines added to the 3’ end for protection.
AKA poly-A tail
What is poly-A polymerase?
An enzyme that binds to mRNA’s polyadenylation signal. IT adds ~200 adenines to the 3’ end.
What is poly-A-binding protein?
Binds to the poly-A tail, protecting the mRNA and helping carry it to the cytoplasm
What are the 2 common RNA nucleotide editing events?
C->U editing. Cytosine is converted to uracil
A->I editing: Adenine is converted to Inosine (I), which is read like a guanine.
