Control of sugar uptake in Gram negative bacteria Flashcards
What is meant by catabolite repression?
The inhibition pf activity/synthesis of catabolic systems in the presence of a readily metabolised carbon source
What is diauxic growth?
Where, in the presence of two carbon substrates, the organism will utilise the “better” substrate first. e.g. E.coli will use glucose over lactose
What does each component of the lac operon code for?
lacI: codes for repressor, has its own promotor
lacZ: codes for ß-gal, for hydrolysis of lactose to glucose and galactose
lacY: codes for lactose permease, involved in the transport of galactosides via H+ symport
lacA: codes for galactoside transacetylase, transfers an acetyl group from acetly CoA to hydroxyl group of galactosides. Not essential for lactose metabolism but is physiologically important for maintaining cell viability
What is the inducer of the lac operon?
In nature, allolactose. Formed by a minor reaction catalysed by ß-gal
In lab, IPTG, a gratuitous inducer which induces enzyme synthesis without being metabolised by the system, thereby showing that induction and metabolism are separate processes
What is meant by inducer exclusion?
Where glucose inhibits uptake of lactose
What are cAMP levels like in fast/slow growing cells?
cAMP levels low in fast growing cells
cAMP levels high in slow growing cells
How is cAMP synthesised?
From ATP, catalysed by adenylate cyclase
What does the CRP/cAMP complex do?
Control catabolic gene expression
How does the cAMP/CRP complex control catabolic gene expression?
CRP binds cAMP causing a conformational change meaning the complex can then bind to specific sequences at the promoters of genes they control
Transcription of the gene is activated following protein-protein interactions with RNA pol
What factors affect the efficiency of transcriptional activation?
The degree of approximation of binding sequence to consensus CRP binding sequence
Positioning of sequence relative to -10 and -35 promoter sequences
What effect does glucose have on lactose metabolism?
Presence of glucose represses lactose metabolism
What are the characteristics of both “tight” and “leaky” ptsI and ptsH mutants?
“Tight” mutants unable to grow on PTS substrates and also cannot be induced to synthesis catabolic enzymes (and transport systems) for lactose, glycerols, maltose, and melibiose
“Leaky” ptsI and ptsH mutants grow normally on non-PTS substrates but are severely repressed by very low concentrations of glucose
