How can we know that the RNA world once existed?
During DNA replication, an RNA primer must be laid down before DNA nucleotides can be added. Deep conservation across life, like ribosomes that are highly conserved across archaea, bacteria. RNA is capable of storing information and catalyzing reactions.
List the post-transcriptional steps that transition pre-mRNA to mature RNA.
5’ capping.
What is the function of the Shine-Dalgarno Consensus sequence?
Functions as the ribosome binding site on the mRNA molecule in bacteria
What makes the spliceosome
Consists of 5 small ribonucleoproteins.
The spliceosome is made of small nuclear RNAs (snRNAs) and proteins, which together form small nuclear ribonucleoproteins (snRNPs). These snRNPs (like U1, U2, U4, U5, and U6) work together to remove introns from pre-mRNA during RNA splicing
What is the function of the spliceosome
The spliceosome removes introns (non-coding regions) from pre-mRNA and joins the exons (coding regions) together.
Describe two types of alternative processing pathways
alternative splicing of pre-mRNA introns or alternative cleavage of 3’ cleavage sites in a pre-mRNA molecule containing two or more cleavage sites for polyadenylation.
What is alternative splicing and its results
The spliceosome removes introns in different ways that can combine different sets of exons. This creates different mature mRNA from the same pre-mRNA
Alternative 3’ cleavage
different 3’ ends are cut- mRNA of different lengths - different proteins.
Function of bacterial ribosomes and eukaryotic ribosomes.
both are made of rRNA + proteins, Bacterial ribosomes are smaller (70s) while eukaryotic is larger and both build protein during translation.
Describe mRNA of a bacterial cell.
mRNA translated as soon as its made, transcription and translation occur together in the cytoplasm, no introns, no 5 cap or poly A tails, Shine dalgarno sequences help ribosomes attach.
Describe mRNA of eukaryotic cells.
Must be processed before translation, transcription occurs in nuclues, translation occurs in cytoplasm, contains introns that must be spliced out, has a 5 cap and a poly A tail, Kozak sequences help ribosomes attach.
What is the impact of a wobble position
makes the genetic code redundant and error tolerant, helping prevent harmful effects from point mutations.
