3rd year revision Flashcards
What type of transport/translocation is rare in bacteria?
Facilitated diffusion (except glycerol)
What is primary translocation?
Where translocation is linked to a biochemical reaction. E.g. group translocation, enzyme-linked solute translocation
What is secondary translocation?
Where translocation is linked to metabolism indirectly via an ion gradient, e.g. uniport, symport, antiport
What is group translocation?
A type of primary translocation. Chemical modification occurs concurrently with translocation, e.g. PTS
What is enzyme-linked solute translocation?
A type of primary translocation. Substrate is not modified but translocation is the result of biochemical reaction
What type of group translocation is found only in bacteria?
The PEP-dependent carbohydrate phosphotransferase system (PTS)
What carbohydrates are often translocated in the PTS?
Hexoses, hexitols, disaccharides
What is PEP?
Phosphoenolpyruvate; the source of energy in the PTS
How is the PTS energy-efficient?
The substrate is phosphorylated as it enters the cell, so the combined transport and modification is energy-efficient
What type of bacteria often utilise the PTS?
Obligate and facultative anaerobes because it is an energy-efficient process
Draw basic diagram of PTS
DO IT
What are the properties of Enzyme I and HPr?
Are soluble, cytoplasmic proteins’ general PTS proteins; are required for all phosphotransferases in the cell
What are the properties of the Enzyme II complex and its domains?
Is sugar specific, consists of several domains, may be parts of a single polypeptide chain or separate proteins
IIA domain: contains the first phosphorylation site
IIB domain: contains the second phosphorylation site
IIC domain: membrane-associated, involved in translocation of substrate, no phosphorylation
(IID domain: present in some systems, translocation)
What else is the PTS centrally involved in?
Metabolic regulation and as an environmental sensor
Is the lac operon positive or negatively controlled, and what does this mean?
Negatively controlled, so involves a repressor.
What is the basis of a negatively controlled operon?
In the absence of an inducer, repressor prevents expression of structural genes
In the presence of an inducer, repressor cannot bind to operator so gene expression occurs
What is the inducer in the lac operon?
In nature, the inducer is allolactose (not lactose), formed via a minor reaction by ß-galactosidase
In lab, IPTG, induces enzyme synthesis but is not metabolised by the system (shows induction and metabolism are independent processes)
Draw structure of lac operon
DO IT
What are the properties of each component of the lac operon?
lacI codes for repressor, has its own promoter
lacZ codes for ß-galactosidase; hydrolysis of lactose –> glucose + galactose
lacY codes for lactose permease; a transmembrane protein which helps lactose get into the cell
lacA codes for galactoside trans-acetylase which transfers an acetyl group from CoA to hydroxyl group of galactosides, is not used for lactose metabolism but is physiologically important for maintaining viability of cell
What is required for formation of allolactose?
Basal level of both lactose permease (LacY) and ß-galactosidase (LacZ)
What is diauxic growth?
Where the bacterium uses the “best” carbon source first, e.g. E.coli growing on a medium containing glucose and lactose will utilise glucose first
What is catabolite repression?
The repression of catabololic enzyme synthesis by a “good” (readily utilised) carbon source, therefore, conserves energy by ensuring that enzymes for utilisation of the non-preferred carbon source aren’t synthesis unnecessarily
When glucose is present in high concentration, what is the cAMP concentration like?
Low
What happens to cAMP as glucose concentration decreases?
cAMP concentration increases correspondingly
What can high levels of cAMP do?
Activate lac operon
How is cAMP synthesised?
From ATP by adenylate cyclase
What was observed in adenylate cyclase mutants?
Cannot make cAMP so cAMP conc low
Mutants unable to use lactose, maltose, xylose (repressed carbon source)
Other mutants were unable to use repressed carbon sources to support growth but had normal cAMP levels. What discovery did this observation lead to?
Identification of cAMP receptor protein (CRP/CAP), a regulatory protein dependent on cAMP
What does the cAMP/CRP complex do?
Activates transcription of catabolite response operons (positive control)`
What is the PEP-dependent PTS?
A type of group-translocation used by prokaryotes to transport and phosphorylate various carbohydrates, particularly hexoses, hexitols, and disaccharides
