Metabolic optimization in Yeast

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Metabolic optimization in Yeast
Cellular economy is the guiding principle.
How does yeast implement this principle ?
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Central Metabolic Pathway
Glucose
Ethanol (yeast)
Pyruvate
Lactate (RBCs, Muscles)
Acetate (2 carbon unit)
Citrate (6 Carbon unit)
Oxaloacetate (4 Carbon unit)
TCA
Mitochondria
O2
a-Ketoglutarate
NH3
2CO2H2O
Glutamate
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Glucose
Pyruvate
Ethanol (yeast)
Acetate (2 carbon unit)
Citrate (6 Carbon unit)
Oxaloacetate (4 Carbon unit)
TCA Mito.
O2
a-Ketoglutarate
NH3
2CO2H2O
Glutamate
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Cell density
Glucose
Time
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Gal
Kinase
Gal-1-phosphate
UDPGlu
Epimerase
Transferase
UDPgal
Glu-1-phosphate
Ethanol
Mutase
Glu-6-phosphate
Glycolysis
Pyruvate
Mito.
Glucose
O2
CO2H2O
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Gal
Kinase
Gal-1-phosphate
UDPGlu
Epimerase
Transferase
UDPgal
Glu-1-phosphate
Ethanol
Mutase
Glu-6-phosphate
Glycolysis
Pyruvate
Mito.
Mannose
Glucose
O2
CO2H2O
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Enzymes required to convert galactose to glucose
6-phosphate are absent when cells are growing in
glucose (fermentable carbon source) or in any
of the non-fermentable carbon source (eg.
glycerol/ethanol)
Galactose metabolizing enzymes are expressed
when yeast cells growing in non-fermentable
carbon but not glucose are exposed to galactose
Glucose is the most preferred source of carbon
and energy
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• Grow the cells in say ethanol

• Add galactose to the above cell culture

• Measure the activity of any one of the enzymes
  of galactose metabolism as a function of time

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Time
galactose
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• How does galactose activate the expression of
• enzymes required for its own degradation ?
• In other words what is the mechanism of
• enzyme induction ?

• How does glucose interfere with the expression
  of
• enzymes required for galactose metabolism ?

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Galactose
Ethanol
Cytoplasm
Galactose
Energy Carbon
Nucleus
Chr
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"If it could be demonstrated that any complex
organ existed which could not possibly have been
formed by numerous, successive, slight
modifications, my theory would absolutely break
down."
Charles Darwin
Never say, and never take seriously anyone who
says, I cannot believe that so-and-so could
have evolved by gradual selection. I have
dubbed this kind of fallacy the Argument from
Personal Incredulity.
Richard Dawkins