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BIOLOGY 1A03 Lecture Notes - Gene Expression, Model Organism, Prokaryote

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Lovaye Kajiura

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Biology Chapter 17: Control of Gene Expression in Bacteria
Gene Regulation and Information Flow
Gene expression occurs when a gene product is actively being synthesized and used in a
Regulation of gene expression is critical to the efficient use of resources and so to
E. coli has served as an excellent model organism for the study of prokaryotic gene
o Like most bacteria, E. coli can use a wide array of carbohydrates to supply carbon
and energy
o Control of gene expression allows E. coli to respond to its environment and
switch its use of sugars
Transcription and translation of genes in bacteria were predicted to be triggered by
specific signals from the environment
Gene expression can be controlled at any step between the synthesis of RNA and the
activation of the final gene product
DNA mRNA protein activated protein
o Arrow from DNA to RNA represents transcription, the making of mRNA
o Arrow from RNA to protein represents translation, in which ribosomes read the
information in mRNA and use that information to synthesize a protein
o Arrow from protein to activated protein represents post-translational
modifications, folding, addition of carbohydrate or lipid groups
How can a bacterial cell avoid producing proteins that are not needed at a particular
time and thus use resources efficiently
o The cell could avoid making the mRNAs for particular enzymes
If there is no mRNA, then ribosomes cannot make the gene product
Ex. Various regulatory proteins affect the ability of RNA polymerase to
bind to a promoter and initiate transcription
Genes that are controlled in this way are said to undergo transcriptional
o If mRNA for an enzyme has been transcribed, the cell might have a way to
prevent the mRNA from being translated into protein
Mechanisms that alter the length of time an mRNA survives before it is
degraded by ribonucleases, that affect translation initiation or that affect
elongation factors and other proteins during the translation process are
forms of translational control
o Some proteins are manufactured in an inactive form and have to be activated by
chemical modifications, such as the addition of a phosphate group
This type of regulation is post-translational control
All three of the controls occur in bacteria
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