Lecture 11

Lecture 11 - PLB 113 Lecture 11 IV. Chloroplast Biogenesis...

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PLB 113 – Lecture 11 IV. Chloroplast Biogenesis E. Protein Targeting to Chloroplast F. Protein Transport G. Transit Peptide Receptor Review: Cosuppression is another form of the phenomenon known as RNAi. High level of mRNA induces RNA dependent RNA polymerase = RNA polymerase synthesizes the complementary strand to the mRNA that’s in high level = dicer (endonuclease) cleaves the dsRNA into small fragments of RNA (siRNA) = siRNA is incorporated into RISC complex = RISC complex is guided by siRNA to chop off the target mRNA (which is complementary to the guide RNA) This is a form of post -transcriptional regulation – occur after the mRNA is transcribed. * siRNA also generates mechanism for inhibiting gene expression at transcription level. siRNA causes some of the genes to be methylated (cytosine in DNA sequence will become methylated), which associates with the transcriptional silencing genes. Question of the Day: How could the evolution of RNAi be beneficial to plants? Plant evolve RNAi to protect themselves from virus. (both RNA and DNA) Since virus generates large amount of RNA in some point of the life cycle, which will be converted into dsRNA. Plant recognizes the viral dsRNA, which then kill them off. What we generally refer to when we talk about RNAi: Gene silencing or RNA silencing ----------------------------------------------------------------------- Chloroplast biogenesis Chloroplast genome: 87 genes that encode protein Proteome chloroplast: 3800 proteins in the chloroplast Presumably, all the genes required to make all these chloroplast proteins at one time are in the chloroplast. These genes have moved from chloroplast to the nucleus of the plant cell. Transfer of DNA from chloroplast to the nucleus of the plant cell = horizontal transfer of DNA Other example correlates to it: Tuf A (gene involved in translation factor of chloroplast) In algae: Tuf A is present in chloroplast genome in higher plant (angeiosperm): Tuf A is present in nucleus * higher plant evolved from the algae but both have the same gene (in different location of the cell) Clicker: What's the advantage of eliminating plastid genes or transferring them to the nucleus A. eliminate non-essential genes B. allow for coordinate regulation of chloroplast and nuclear genes C. Reduce chances of accumulating mutation in plastid genes For choice A: when a bacteria it was one time free living now present in the plant cell, some of its functions were taking cared. Thus, it didn't require quiet biochemical reactions needed as free-living bacteria did. Thus, a lot of non-essential genes were eliminated. For choice B: the concept is correct. However, chloroplast itself has all the genes needed in order to
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This note was uploaded on 11/16/2011 for the course PLB 40175 taught by Professor Amenta during the Spring '11 term at UC Davis.

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Lecture 11 - PLB 113 Lecture 11 IV. Chloroplast Biogenesis...

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