Biology 1002B Lecture Notes - Horizontal Gene Transfer, Oxygen-Evolving Complex, Vaucheria

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Published on 21 Apr 2013
School
Western University
Department
Biology
Course
Biology 1002B
Professor
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
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Document Summary

Lecture 22: the elysia/vaucheria system: 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. 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. Photosynthetic function of chloroplast rely on enzymes, protein complexes, cofactors (chlorophyll, iron) Extracted chloroplast can only make its own reduced carbon and oxygen. Extracted chloroplast"s entropy gradually increases and function. Lack access to other important sources of nutrients. Unable to import proteins made in plant"s cytosol in extracted chloroplast also account for decline: lateral gene transfer.

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