Lecture 7 Flashcards
Messenger RNA (mRNA) is complementary to what strand of DNA?
- Template - reverse complement
- Coding - resembles (identical to) transcript
What are the differences between DNA and RNA?
RNA:
* Ribonucleotides (contain sugar ribose)
* Contains uracil (U) instead of thymine (T)
* Single-stranded
DNA:
* Sugar: deoxyribose
* Contain thymine (T)
* Double-stranded
(1) Compare the error rate of RNA polymerase and DNA polymerase. (2) Why isn’t this difference very consequential?
(1)
* RNA polymerase - 10^4 nucleotides
* DNA polymerase - 10^7 nucleotides
(2)
* Error in DNA = everything else gets affected (everything is inherited)
- Error in RNA = nothing is inherited (goes unnoticed)
- RNA is not used as permanent storage form of genetic information
What are noncoding RNAs?
RNA that is final product of a gene and does not code for protein
What is the function of the following types of RNAs: mRNA, rRNA, miRNA, tRNA?
- mRNA - code for proteins
- rRNA - form core of ribosome’s structure and catalyze protein synthesis
- miRNA - regulate gene expression
- tRNA - serve as adaptors between mRNA and amino acids during protein synthesis
What is gene expression?
process by which information encoded in a DNA sequence is converted into a product (RNA or protein)
(1) What is a promoter? (2) Is it transcribed?
(1) DNA sequence that initiates transcription
(2) No
What is the purpose of the sigma factor?
Responsible for recognizing promoter sequence on DNA
RNA polymerase always move in the __________ direction with respect to the template DNA strand.
3’-to-5’
mRNA synthesis requires a ________ (not a primer) to begin transcription
promoter
What are the differences between initiation of transcription in eukaryotes and bacterial?
Bacteria:
* 1 RNA polymerase
* Rely on sigma factor to initiate transcription
Eukaryotes:
* 3 RNA polymerase
* Require general transcription factors
What are the three types of RNA polymerase in eukaryotic cells? What do each transcribe?
- RNA Pol I - rRNA
- RNA Pol II - mRNA
- RNA Pol III - tRNA
What are the two locations of the RNA Pol II promoter?
- -35
- -30
What two components are needed for the formation of the initiation complex in eukaryotes?
- General transcription factors
- RNA polymerase II
Which of the below is the coding strand? The template strand? The transcript?
(1) B - resembles mRNA transcript (exception of T not U)
(2) C
(3) A - has uracil; single strand
When RNA pol is moving along, it’s synthesizing transcript in what direction? What direction along template strand?
(1) 5’-3’ direction
(2) 3’-5’ direction
What will be the second anti-codon, codon, and its corresponding amino acid for the transcript below?
GCC (codon) –> GGC (anticodon); Alanine
(1) To what sequence will a release factor bind to in the transcript below? What will be the terminating amino acid? Where will the release factor bind in the ribosome?
(1) UAG (stop codon)
(2) GAU (Asp)
(3) A site
What anticodon will have left the E site once the release factor engages its site?
GGA
When is the only time tRNA binds to P site?
Initiation
Describe the RNA transcript.
- RNA chain produced by transcription
- Single-stranded
- Complementary to template strand
What is the coding strand?
Sequence is equivalent to RNA product
What direction is the RNA chain elongated in?
5’-to-3’ direction
What is the difference between RNA polymerase and DNA polymerase?
RNA polymerase:
- Catalyzes linkage of ribonucleotides
- Do not need a primer
- Do not accurately proofread
What are the three steps of RNA processing?
- RNA capping:
- Modifies 5’ end of RNA transcript
- Guanine (G) with methyl group attached to 5’ of RNA - Polyadenylation:
- Enzyme adds a series of repeated adenine (A) to 3’ end (poly-A tail) - Splicing:
- Introns are removed from RNA
- Exons are stitched together
What are snRNAs?
RNA molecules that carry out RNA splicing
What is the spliceosome?
Assembly of RNA and protein that carries out RNA splicing
Explain the process of RNA splicing. How do snRNPs contribute to this process?
- U1 binds to 5’ splice site
- U2 binds to branch point
What is alternative splicing?
Splicing transcript in different ways to produce different proteins from same gene
What proteins bind to mature mRNA?
- Poly-A-binding proteins
- Cap-binding protein
- Exon junction complexes
What is the 3’ untranslated region (UTR)?
Region that lies between 3’ end of coding sequence and poly-A-tail
What is the difference between general and gene-specific transcription factors?
- General transcription factors - requires for setting up transcription apparatus
- Gene specific factors - binds to enhancer sequence (enhances basal levels)
What is the order that general transcription bind? Which one carries RNA polyermase?
D → B → E → H, F comes in w/RNA Pol
How is elongation promoted in eukaryotes? Prokaryotes”
Eukaryotes: phosphorylation of C-terminal tail
Prokaryotes: sigma factor is released from RNA polymerase
In bacteria transcription and translation are coupled. What does this mean?
Translation happens at the same time transcription is happening
In eukaryotes they are uncoupled - what does that mean?
transcription in nucleus before ribosome can begin translation
Compare introns and exons.
Introns:
- Long, noncoding, intervening sequences
- Typically much larger than exons
Exons:
- expressed sequences
What is the importance of capping and polyadenylation of mRNA in eukaryotes”
- Increases the stability of eukaryotic mRNA
- Facilitate export from the nucleus and protein synthesis
What are key mechanistic differences in gene expression between eukaryotes and prokaryotes?
Prokaryotes - coupled (transcription + translation occur at the same time)
Eukaryotes - uncoupled
Where is mRNA degraded?
Cytosol
the poly A tail is not encoded in genome. It must be added by what enzyme?
Poly A polymerase (PAP)
