BIOL2161 Lecture Notes - Lecture 13: Alternative Splicing, Ricin, Hydrolysis
BIOL6: Genes: Replication and
Expression
Block 3: Gene structure & regulation in eukaryotes
• Ricin:
o Isolated from plant
o Seeds contain ricin (they look like ticks)
o Inhibitor of the ribosome
• Hydrolyses adenine of 28s RNA
• Part of the RNA is cleaved, and therefore the ribosome is inactivated
o Extremely powerful: 1 molecule of this toxin will inhibit 1500 ribosomes/min
RNA Processing
• Prokaryotes: Transfer of information is form DNA to (m)RNA to proteins
• Eukaryotes: transfer of information is DNA to pre-mRNA, after process of RNA splicing, mature
RNA is produced and exported to cytoplasm where translation takes place to form protein
• Drosophila courtship and mating behaviour
o
• Singing only in males not females
o What is the molecular basis for song only in males?
• Alternative splicing: same genetic make-up, different behaviour
▪ ♂ (male) full-lengths protein
▪ ♀ (female) alternative splicing: stop codon -> truncated, non-functional
protein
▪ fruitless (fru): (mutated in males): can’t discriminate between ♂ and ♀
▪ Whole complex behaviour controlled by alternative splicing
▪ Females with full length protein show this complex behaviour (mutant
female tries to get attention of wild type female)
• How was alternative splicing discovered
o Is the number of nucleotides proportional to the number of amino acids?
find more resources at oneclass.com
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• Evidence against
▪ Genes and proteins are colinear: that not all RNA strand ends up in the
protein
▪ More DNA than required for proteins (eukaryotes)
▪ Large RNA molecules in nucleus were shorter in cytoplasm
▪ DNA hybridised with its mRNA:
• made DNA single stranded and put mRNA near it, mRNA hybridised
with DNA to form a double strand
• Then was clear that there were loops of still single stranded DNA
(intron) that did not correspond to complimentary RNA strand, and
was spliced out
•
• Actual processing of mRNA: 4 main mechanism to produce mature/processed mRNA strand
o Addition of the 5' cap
• Usually it’s a 3' to 5' likage i RNA, ut i this ase it’s a 5' to 5' likage - More
stable
• Helps to stabilise mRNA
• Eukaryotes bring in guanine nucleotide
• And then this last guanine group is methylated (to form 7-methyl guanine), as are
the previous 3 bases (with 2' methyl group)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Block 3: gene structure & regulation in eukaryotes: ricin: Isolated from plant: seeds contain ricin (they look like ticks) Inhibitor of the ribosome: hydrolyses adenine of 28s rna, part of the rna is cleaved, and therefore the ribosome is inactivated, extremely powerful: 1 molecule of this toxin will inhibit 1500 ribosomes/min. Rna processing: prokaryotes: transfer of information is form dna to (m)rna to proteins, eukaryotes: transfer of information is dna to pre-mrna, after process of rna splicing, mature. Rna is produced and exported to cytoplasm where translation takes place to form protein: drosophila courtship and mating behaviour. Females with full length protein show this complex behaviour (mutant female tries to get attention of wild type female: how was alternative splicing discovered. Increases stability of the transcript (protect 5" end from nucleases) Self-splicing introns in protists and mitochondria (unicellular eukaryotes): remove themselves (no other enzyme/protein: at least 15% of mutations that case human disease affect mrna splicing.
