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Lecture 30

BIOL 2030 Lecture 30: Catabolite Repression and Transcriptional Termination

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BIOL 2030
Herbinger Christopher

Lecture 30 - Catabolite Repression and Transcriptional Termination March 31, 2017 12:31 PM Catabolite activator protein - many operons controlled by a single regulatory protein  If lactose is provided to the cell, there would be a sudden rapid induction of enzymes involved in lactose metabolism o If glucose is provided the same cell, with the increased amount of enzymes involved in lactose metabolism, the amount of enzymes are then decreased - glucose shuts it off o This is true even if it was any sugar added to the cell - if glucose is added immediately after the increase of enzymes, the glucose shuts off the gene, decreasing the amount of enzymes  E. coli cells grow much more rapidly in glucose than in lactose o Is more energy extracted from glucose than lactose?  Answer is no - but net energy in the cell, yes!  Protein synthesis requires energy  Lactose is broken down into galactose and glucose  The pathway to break down glucose into energy is on all the time - the enzymes are made all the time, so they are constitutively expressed enzymes  If both lactose and glucose are given into the cell - it would be a waste of energy to break down lactose into glucose and galactose, in order to break glucose down even further  It would be better to just use energy to break glucose down immediately  Growth rate of E. coli on various carbon sources o cAMP - cyclic adenosine monophosphate  Levels of cAMP are based on carbon sources - low in glucose, high in lactose (for example) o Intracellular concentration of cAMP in the bacterial cell is carefully maintained by rates of enzymatic synthesis and degradation o Glucose inhibits the intracellular activity of cAMP  Catabolite activator protein (CAP) o Region is called the CAP binding site, and needs both cAMP and CAP to be bound to each other, in order to activate a gene o Lactose operon not only needs the active repressor to be off the operon, but also the catabolite activator protein as well for maximal initiation  Needs CAP to open up the operon to allow RNA polymerase to bind to operator o If glucose and lactose are in growth medium:  Repressor is not bound (deactivated by allolactose) but by itself, it cannot initiate transcription - needs CAP  But because glucose is present, it inhibits the synthesis of cAMP, CAP is unable to bind to binding site o If glucose is in the cell, but lactose is not  cAMP levels are low, CAP cannot bind  Because there is no lactose present, allolactos
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