Gene transcription and RNA modification - RNA modification
41 important questions on Gene transcription and RNA modification - RNA modification
What has been called the colinearity of gene expression?
Why is the colinearity of gene expression not (entirely) true?
What process is needed to produce mature mRNA out of a pre-mRNA, and what happens during this process?
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Does splicing occur in both eukaryotic and prokaryotic species?
Is RNA modification the same as RNA splicing?
Where does processing occur in eukaryotes?
For the production of tRNA molecules, which kind of enzymes are needed?
What is the difference between exoncleases and endonucleases?
What kind of endonuclease and exonuclease can be involved at the processing of a tRNA?
What did scientists discover about RNaseP in 1983?
How is an enzyme like RNaseP called?
What is RNA splicing?
In what kind of RNAs and in what species does RNA splicing occur?
What is the difference between the group I, group II and pre-mRNA introns?
How does splicing of group I introns occur?
- The guanosine breaks the bond between exon 1 and the intron.
- The guanosine becomes attached to the 5' end of the intron.
- At the 3' end of exon 1 is an OH-group, which breaks the bond next to a nucleotide between the end of the intron and exon 2.
- Exon 1 forms a covalent bond with the 5' end of exon 2.
What is the difference between the splicing of group I introns and group II introns?
Which proteins in eukaryotes often enhance the rate of self-splicing?
Pre-mRNA introns are not self-splicing. What do they need then?
What is the function of the spliceosome in the splicing of pre-mRNA?
How many introns does an average human gene have?
Of what 5 subunits is the spliceosome composed?
What are these subunits called and where does that name come from?
How does the spliceosome recognize the intron-exon boundaries?
Which of the 5 subunits cleaves the RNA at the exon-intron boundaries and connects the remaining exons?
Splicing costs a huge amount of energy. This implicates that it must have a biological advantage (due to natural selection). What is a biological advantage of pre-mRNA splicing?
How many percent of the human pre-mRNAs are alternatively spliced?
A pre-mRNA that can be alternatively spliced, as two types of exons. Which two types are these?
- Alternative exons, exons that vary from one cell type to another.
Alternative splicing is not random. What proteins are involved in the regulation of alternative splicing?
In which two ways can splicing factors modulate the ability of a spliceosome to choose 5' and 3' splice sites?
- Other splicing factors enhance the ability of the spliceosome to recognize particular splice sites (which are not automatically recognized).
What forms the basis for alternative splicing outcomes?
2. Splicing factors are regulated by the binding of small effector molecules, protein-protein interactions and covalent modifications.
On which types of RNAs does capping occur?
In which 3 steps does capping occur?
2. An enzyme, guanylyltransferase, hydrolyzes guanosine triphosphate and attaches a guanosine monophosphate to the 5' end;
3. An enzyme, methyltransferase attaches a methyl group to the nitrogen at position 7 in the base guanine.
What are the functions of the cap?
- The cap is recognized by initiation factors that are needed during the early stages of translation;
- The cap may be important in the efficient splicing of introns.
The polyA tail is not encoded in the gene sequence. How is it then added at the 3' end of the mRNA?
What is the consensus sequence for the polyadenylation signal near the 3' end of the pre-mRNA?
Of which 2 steps does polyadenylation consist?
2. PolyA-polymerase adds adenine nucleotides to the 3' end.
What is the function of the polyA tail?
- Facilitates stability of mRNA in the cytosol
- Facilitates translation.
On what kinds of RNAs does polyadenylation occur?
What is RNA editing?
- additians or deletions of particular bases
- conversion of one type of base to another.
What kind of molecule do you get when cytosine is deaminated? And what when adenine is deaminated?
- When adenine is deaminated, hypoxanthine (H) is formed (which is recognized as guanine during translation).
What kind of effects can RNA editing have?
(When a stop codon is generated, the protein is much shorter then it would be without RNA editing).
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