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Lecture 22.docx

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Western University
Biology 1002B
Denis Maxwell

Lecture 22: The Elysia/Vaucheria System 1. Recall that the surprising ability of the “solar slug” Elysia to maintain functional chloroplasts stolen while feeding on Vaucheria algal cells (kleptoplasty) is an unsolved mystery in science. One possibility is that genes required for plastid maintenance have undergone evolutionary lateral gene transfer from the nucleus of the algae to the nucleus of the slug. This lecture was designed to analyze a primary research article and showcase how the authors used selected DNA technologies to generate data in support of their hypothesis that a particular photosynthetic gene (psbO) from the nucleus of Vaucheria is also present in Elysia. Overall, you should be able to i) identify the various types of data shown by this paper; ii) explain how these data were obtained; and iii) conclude whether each type of data does, or does not, support the hypothesis. 2. If you isolate chloroplast, photosynthesis decreases at a constant rapid pace but in elysia, it declines slowly in a straight line, why?  Photosynthetic function of chloroplast rely on enzymes, protein complexes, cofactors (chlorophyll, iron)  Photosynthesis does not provide all the nutrients it needs (i.e. minerals) o Why most plants have their roots in the soil to absorb those nutrients o Variety of nutrients increases entropy inside chloroplast o For chloroplast to function, food is needed to maintain low entropy  Extracted chloroplast can only make its own reduced carbon and oxygen  Lack access to other important sources of nutrients  Extracted chloroplast's entropy gradually increases and function  Unable to import proteins made in plant’s cytosol in extracted chloroplast also account for decline o Lateral gene transfer  Chloroplast in Elysia, has evolved ways to absorb its needed nutrients from its host o Mutations which lead to expression of new transporters  ROS destruct nuclear coded proteins or broken or degraded due to half life o Without presence of nuclear DNA these proteins cannot be replaced and lose functionality  Without the mitochondria, ATP from chloroplast ETC may not be enough to function  Isolated chloroplasts in a much different environment o No ability to perform phototaxis since no eyespot to detect light 3. Location of PsbO gene in photoautotrophic organisms  Genes for both organelles found in the nucleus in vaucheria  Elysia only has genes for mitochondria and none for chloroplast o Horizontal/lateral gene transfer of PsbO gene 4. Location and role of PsbO gene product in photosynthetic electron transport  Gene in nucleus codes for evolving of oxygen from splitting water in ETC  Part of oxygen evolving complex  Required for photosystem II to work 5. Purpose of molecular size markers in electrophoresis  To identify the different sizes of proteins 6. Interpretation of agarose gel data  Slight band indicating slight expression of psbO in Elysia in nucleus after 5 months of feeding o mRNA doesn’t stay for that long so proof that gene was there before  Bands is the amplified portion of mRNA (transcript) o Ignore original due to many introns  Size of amplified DNA determined by comparing position of known size separated on gel o If size matches predicted size for target DNA, PCR is successful 7. Mechanism of polymerase chain reaction  Special case of DNA replication in which DNA polymerase replicates just a portion of DNA only o A primer based paired to template for replication to begin by adding nucleotides to 3’ end  PCR based on specificity of primer binding  Amplification of specific DNA o Produces many copies of specific DNA without having to clone the sequence in a host organism
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