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Lecture 22.docx

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Biology 1002B
Tom Haffie

Lecture 22: the Elysia/Vaucheria System  Elysia feed on Vaucheria and steals Vaucheria’s chloroplast  Horizontal gene transfer (lateral gene transfer) of the algal nuclear gene psb0 to the photosynthetic sea slug Elysia Chlorotica  Photosynthetic competency o Those chloroplast remain highly photosynthetic even after 80 days o But isolated systems like chloroplast from spinach it’s done after 12 hours  Why does chloroplast photosynthesis go down as time goes on, why doesn’t it stay constant? o Check online  Horizontal (lateral) gene transfer o Genes from mitochondria and/or chloroplast transfer to the nucleus o Or genes from one organism transfer to another organism o Vaucheria  Nucleus code for most of the genes of chloroplast and mitochondria o Elysia  Nucleus and mitochondria, but it takes in chloroplast o Hypothesis was that is there lateral gene transfer from Vaucheria of photosynthetic gene of psbO to Elysia o The paper showed that there was a lateral gene transfer of psbO from Vaucheria to Elysia, transfer might’ve happened many years ago o Elysia takes in Vaucheria, chews everything up but chloroplast, maybe it chews a bit of nucleus and incorporated into its own genome  Vertical gene transfer o Parent to offspring transfer  PsbO encodes a component of PSII o Gene resides in the nucleus o Part of the oxygen evolving complex o PSII won’t work if there’s no psbO  Expression of psbO in Elysia o Agarose gel electrophoresis o Amplified portion of psbO transcript o Always look at the transcript (never look at exon or introns) o Start with the mRNA o The expression of a transcript of psbO is present in Voucheria and Elysia o 452 bp fragment o 5 months after feeding o Very doubtful that the transcript can last 5 months, so thus it is not the content that the Elysia ate from Voucheria, that Elysia is acutally producing the transcript  Polymerase Chain Reaction (PCR) o Kary Mullis  Nobel prize chemistry 1993 o Amplification of specific DNA  Taq DNA polymerase  Two Primers (1 – 30 bp long)  dATP, dGTP, dCTP, dTTP o Forensics, gene studies…  PCR reaction cycle o Start with double stranded DNA o Denaturation  High temperature (94 – 100 degree Celsius)  To separate the double strands into single stranded DNA o Annealing  Hybridization of primers  Cool it off a bit (45 – 65 degree Celsius)  Primers are gene specific  Amplify the genes between the primers  The synthesized primer will bind on to the single stranded DNA o Extension  DNA synthesis from primers  Heat it up a bit for the protein to extend the DNA strand (72 degree Celsius), where polymerase work at best  Protein (polymerase) binds to the primer and extend it o This is one cycle, and we can do it over and over again o After 30 cycles… amplification of 1 billion times o Small sample can be amplified billions of times o So what?  Give so much amplification, we can see it on a stain gel  We can do lots of things with this  PCR is based on specificity o PCR based on specificity of primer binding o In any DNA sequence  1 in 4 chance of finding an A, G, C or T  1 in 16 chance of finding any dinucleotide sequence  1 in 256 chance of finding a given 4 – base sequence  1 in 4^16 chance of finding a given 16 – bas
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