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INDM 3007

INDM 3007. Lecture 3. Light harvesting pigments. Reaction centre. Harvesting of light energy by phototrophic bacteria. Photosynthetic genes. In Rhodobacter capsulatus the LHP are more abundant than the reaction centre proteins. However, the genes are organised in an operon: 1 promoter.

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INDM 3007

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  1. INDM 3007 Lecture 3

  2. Light harvesting pigments Reaction centre Harvesting of light energy by phototrophic bacteria

  3. Photosynthetic genes In Rhodobacter capsulatus the LHP are more abundant than the reaction centre proteins However, the genes are organised in an operon: 1 promoter

  4. pufBA mRNA is more stable than pufLMX mRNA due to the hairpin structure

  5. Photosynthetic growth of R. capsulatus Photosystem is oxygen sensitive; ie they are inactivated in presence of oxygen Light Dark Oxygen NO NO No Oxygen YES NO Expression of puf Genes only required under anaerobic growth conditions in the light

  6. Light + oxygen R. capsulatus Dark + no oxygen Phototrophs like R. capsulatus live in sediments of lakes etc Access to light and being anaerobic means living at an interface: very dynamic environment Growth conditions change frequently AND rapidly

  7. Stable mRNA allows many rounds of translation. What if the growth conditions suddenly change??? R. capsulatus has a specific endonuclease degrading pufBA genes in presence of oxygen Half-life of mRNA reduced to 2 minutes

  8. Regulation of mRNA stability is an example of Post transcriptional regulation It allows to cell to regulate gene expression after transcription has occured Fine tuning of expression levels Rapid adaptation to changing environmental conditions

  9. Translation overview Initiation Specific binding of the 30S and 50S subunits to the translation start of mRNA binding of 1st amino acyl tRNA Elongation Ribosome 'reads' mRNA, catalyses formation of peptide bonds binds charged tRNA and releases uncharged tRNA Termination Ribosome stops translation at specific point release of polypeptide chain dissociation from mRNA

  10. Translation Initiation

  11. The Shine-Dalgarno sequence is complementary to a sequence in the 3' end of 16S rRNA in the small subunit of the ribosome! Translation initiation is dependent on base pairing between mRNA and rRNA Bacteria employ post-transcriptional regulation mechanisms which interfere with mRNA rRNA base pairing

  12. Most simple mechanism: variation in Shine Dalgarno sequence mRNA is not differentially unstable, yet there are different ratios of proteins

  13. Translational repressor

  14. Anti-sense mRNA The sequence of genR is complementary to the ribosome binding site of genX genX genR

  15. Antisense mRNA is a powerful method to prevent gene expression is widely used as method for treating disease and controlling traits in for example plants

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