Nucleic acids 5- Small RNAs Flashcards
What is the c value and c-value paradox?
C-value = genome size
The complexity of an organism is not necessarily related to its genome size (C-value).
How much non coding RNA is functionally active?
20%
What is non coding RNA?
Any RNA molecule that is NOT TRANSLATED into a protein. (i.e. does not include mRNA)
What is the role of antisense RNA?
If there is a gene you want to block, you can transcribe a reverse of the gene to make an ANTISENSE RNA STRAND.
The antisense and sense RNA strands will hydrogen bond to form a double strand.
Therefore, sense RNA cannot be translated.
Describe the process of RNAi (rna interference)
DICER breaks up RNA into 21-25bp fragments - Dicer is an Rnase III like endonuclease activity,
‘Passenger’ Strand is removed - siRNA guided, endonuclease activity acts to remove one of the siRNA strand known as the passenger strand. Required ARGONAUTE-PIWI PROTEINS (AGO). The strand that is retained is antisense to the target strand.
Multiprotein, RNA-induced silencing complexes or RISC complexes are formed. They recognise and cleave target mRNA molecules which have complementary sequences to the incorporated single-stranded guide siRNA.
What happens when the DICER gene isnt present in mammals
lethality in early embryonic stages because embryonic stem cells are unable to differentiate leading to a depletion of multipotent stem cells.
This leads to: limb morphogenesis defects, lung development defects, incomplete embryonic myogenesis, epidermal hyperproliferation`
What is the role of miRNAs
There are miRNAs in the genome that are involved in regulating other genes. It’s another level of gene regulation.
describing the processing and transcription of miRNAs
miRNAs are not made as very small RNAs. They are made as much bigger RNAs called pri-miRNAs and pre-miRNAs.
Pri-miRNA is processed and chopped up a little and is exported into the cytoplasm as pre-miRNA.
Processing allows the pre-miRNA to be passed down into the RISC complex
IMPORTANT: THERE ARE SEQUENCES IN THE pre-miRNA THAT END UP AS siRNA IN THE RISC COMPLEX.
Once the pre-miRNAs become miRNAs they can target genes at an RNA level and silence genes.
This is called gene knockdown - decreasing the amount of protein you get from a gene.
To summarise: A lot of transcriptional activity in genome makes pri-pre miRNA which is edited down to miRNA which is eventually used to control other genes.
What is the seed region
‘Seed Region’ - most important region of the miRNA for targeting. Lies between nucleotide positions 2 to 8 from 5’ end and is often flanked by adenosines.
How are the buldges formed in miRNA bioinformatics
Mismatches, usually in the centre form a bulge, often followed by a less stringent degree of complementarity in the 3’ region.
What disease is due to loss of miRNA
chronic lymphoid leukoemia
