L4- RNA Synthesis Flashcards
List three differences between RNA and DNA.
- The pentose sugar in RNA is ribose rather than deoxyribose, 2. RNA has Uracil (U) instead of Thymine (T), and 3. DNA normally exists as a double helix whereas RNA exists as a single strand.
True or False. mRNA typically exists as a single-stranded molecule.
True.
The sequence of RNA transcripts is similar to that of which DNA strand?
The coding strand (also called the (+) strand). The other strand is called the template or (-) strand.
In which direction is RNA synthesized?
5’ to 3’.
Name the three eukaryotic polymerases involved in RNA synthesis.
RNA polymerase I, II and III.
What is the cellular location and function of RNA polymerase I?
It is found in the nucleolus and transcribes 28S, 18S and 5.8S ribosomal RNAs (rRNA).
What is the cellular location and function of RNA polymerase II?
It is found in the nucleus and transcribes pre-mRNA.
What is the cellular location and function of RNA polymerase III?
It is found in the nucleus and transcribes tRNA, 5S rRNA and other small RNAs.
What are the two subunits of eukaryotic ribosomes?
60S and 40S. Each of these is composed of multiple rRNA and protein subunits.
Which two transcription factors are required for RNA polymerase I to bind to and transcribe DNA?
Transcription factors B and S (B for binding, S for stimulating).
What marks the termination site of RNA poly I?
A string of T residues.
What transcription factors are required to recruit and activate RNA poly III?
TFIIIA, TFIIIB and TFIIIC (note that the Roman numeral in the name of the transcription factor tells you which polymerase it is associated with).
What conserved sequence in the promoter region directs Poly II binding? What protein binds this sequence?
The TATA box. The most common sequence is TATAAA. This is bound by the TATA-binding protein (TBP) which is part of TFIID.
What is the purpose of an enhancer sequence?
Enhancers increase the transcription of neighboring genes. They can be located either upstream or downstream of the gene that is to be transcribed.
Which set of transcriptions factors are required for the initiation of transcription?
Basal Transcription Factors.
A methylguanylate (m7G) cap is placed at which end of a nascent RNA strand?
The 5’ end. Note that the m7G residue is linked to the RNA via a 5’ to 5’ triphosphate bond.
Cleavage and polyadenylation occur at which end of a pre-mRNA strand?
The 3’ end.
Which sequence element signals for cleavage of hnRNA and addition of the poly(A) tail?
The AAUAA sequence. This is located approximately 15 nucleotides upstream of the site of cleavage and subsequent polyadenylation.
True or False. Poly A tails are encoded within genes.
False. The tails are added by poly(A) polymerase, a polymerase that does not utilize a template.
What transcription factor reads the AAUAA sequence on pre-mRNA?
Cleavage and polyadenylation specificity factor (CPSF).
What is RNA splicing?
The process by which introns are removed from the pre-mRNA molecule.
What is the spliceosome and what is its function?
The spliceosome is a large ribonucleotide protein complex akin to the ribosome. Spliceosomes contain smaller nuclear snRNPs (U1, U2, U4,U5 and U6). This complex removes introns from pre-mRNA molecules.
What is alternative splicing?
A single pre-mRNA can be spliced in different ways, yielding different mature mRNAs. Thus, a single gene can code for a series of related, but non-identical proteins.
Which rRNAs make up the 40S subunit of eukaryotic ribosomes?
18S rRNA (and proteins).
Which rRNAs make up the 60S subunit of eukaryotic ribosomes?
28S, 5.8S and 5S rRNAs (and proteins).
Which rRNA is synthesized outside of the nucleolus?
5S rRNA (it is synthesized by RNA poly III).
Which RNA polymerase is inhibited by the drug actinomycin D?
Mammalian RNA polymerase I.
Which RNA polymerase is inhibited by the drug alpha-amanitin?
Mammalian RNA polymerases II and III.
Which RNA polymerase is inhibited by the drug rifampicin?
Bacterial RNA polymerase.
True or False. The activation region for the 5S rRNA gene is found within the gene itself.
True.
True or False. Genes that are constitutively expressed contain a TATA box as a promoter.
False. They generally contain a GC-rich region instead.
What is the only basal RNA polymerase II transcription factor that directly binds to DNA?
TFIID.
What is the function of the RNA Gppp cap?
It is believed to protect against the degradation of nascent RNA.
True or False. All RNAs acquire a poly(A) tail following transcription.
False. Only those RNAs that are to become mRNAs acquire a poly(A) tail.
Introns in pre-mRNA typically have ___ residues at their 5’ end and ___ residues at the 3’ end.
GU, AG.
What is the first step of RNA splicing?
Cleavage of the 5’ exon-intron junction by the spliceosome.
What is an intron lariat?
It is an intron that has been circularized with a specific branch point between a 5’ G residue and a 3’ splice-site A residue linked in a 5’ to 2’ bond.
Which small nuclear ribonuclearprotein (snRNP) binds to the 5’ exon-intron junction?
U1.
Which small nuclear ribonuclearprotein (snRNP) binds to the branch point of an intron lariat?
U2.
Which small nuclear ribonuclearprotein (snRNP) binds upstream to the 3’ intron-exon junction?
U5.
