Quiz IV Flashcards
T or F: all genes are expressed into proteins.
F: only some genes are expressed into proteins
What is RNA splicing?
Removal of non-coding intron sequences, leaving coding exons
What is the final result of RNA splicing?
Messenger RNA (mRNA)
What are the main processes that occur during gene expression? Explain what happens during each.
- Transcription - DNA acts as a template for RNA synthesis
- Splicing - removal of non-coding intron sequences, leaving coding exons in RNA transcript
- Translation - Ribosome and tRNA translate codons in mRNA into sequence of amino acids
What are the three types of RNA that play a role in protein synthesis?
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
- Ribosomal RNA (rRNA)
What are codons?
Groups of three nucleotides that specify the amino acid sequence
When does translation occur?
After mRNA travels to cytoplasm
Where is the mRNA positioned on the ribosome?
Small subunit
What type of RNA helps mRNA position on the ribosome?
rRNA
What are the two ends of tRNA?
- Anticodon sequence
- Amino acid
What role does rRNA and the large ribosomal subunit play in translation?
Catalyzing formation of a peptide bond between two amino acids
Catalyzing the formation of a peptide bond between two amino acids is done by which parts of the ribosome during translation?
- rRNA
- Large subunit
What is transcription?
Process of synthesizing RNA from a DNA template
The pre-initiation complex assembles around the _______ of a gene.
Core promoter
What makes up the promoter in eukaryotes?
- TATA box
- Initiator sequence
_________ bind at the TATA box.
General transcription factors
General transcription factors bind at the _________.
TATA box
Which part of the promoter contains the transcription start site?
Initiator sequence
What is the direction of mRNA synthesis?
5’-3’ direction
The newly-created mRNA strand represents a copy of the information in which DNA strand?
Coding strand
What does RNA polymerase do?
Protein that transcribes DNA to RNA
What are the five subunits that make up the RNA polymerase core enzyme?
- Two identical alpha subunits
- One beta subunit
- One beta prime subunit
- Omega subunit
What two components make up the RNA polymerase holoenzyme?
RNA polymerase core enzyme + sigma factor
What are the three polymerases in eukaryotes? What class of RNAs do each transcribe?
- RNA polymerase I - most ribosomal RNA genes
- RNA polymerase II - all protein-encoding genes
- RNA polymerase III - tRNA genes, some snRNA, and other small RNA genes
Which RNA polymerase has a carboxy-terminal domain?
RNA Pol II
What is the function of the carboxy-terminal domain on RNA polymerase II?
Serves as a binding site for transcription factors
The binding of transcription factors to the carboxy-terminal domain depends on ____________.
Phosphorylation
?
RNA splicing removes _____ and attaches ______ together.
Introns; exons
_______ catalyzes RNA splicing.
Spliceosome
What is a spliceosome?
Large assembly of small nuclear ribonucleoproteins (snRNPs)
What are snRNPs made up of?
- Small nuclear RNAs
- Proteins
What are the five snRNPs that make up the spliceosome?
U1, U2, U4, U5, U6
Explain the process of RNA splicing. What does each snRNP do?
- U1 binds 5’ splice site
- Proteins recognize branch point A. Proteins later replaced by U2
- Complex of U4/U6 and U5 binds to 5’ splice junction and assists in bringing 5’ end to branch point A
- 1st transesterification reaction - reaction between branch point A and 5’ splice site creates a lariat
- 2nd transesterification reaction - reaction between 3’ end of upstream exon and 5’ of next exon (cleaves of intron)
Nuclear pore complexes are composed of what class of proteins?
Nuceoporins
Describe the structure of an NPC.
Hollow, cylindrical structure
What does a nuclear transport receptor do?
Associates with mRNA to help it pass through NPC
List the types of junk RNAs in a cell.
- Pre-spliced mRNA
- Excised introns
- Incompletely spliced products
List the proteins that mRNA associates with.
- Cap Binding Complex (CBC)
- Exon Junction Complex (EJC)
- Poly-A-binding proteins
- Heterogenous nuclear RiboNuclear Proteins (hnRNPs)
- SR proteins
Which protein associated with 5’ cap?
Cap binding complex (CBC)
Which proteins associate with Poly-A tail?
Poly-A-binding proteins
Why are junk RNAs unable to pass the NPC?
Junk RNAs cannot bind to proteins that associate with mRNA and as a result remain stalled
Cell can distinguish between correctly processed mRNA by detecting the proteins associated with RNA
Describe the RNA exosome. What is the function and structure?
• Degrades junk RNAs
• RNA protein complex comprised of a barrel-shaped core
What type of activity does the RNA exosome have?
Exonuclease
