chapter 14 - fermentation Flashcards
Fermentation
energy conservation depends on substrate level phosphorylation
What are the two major challenges of fermentation?
- conserves much less energy than respiratory organisms
- difficult to achieve redox balance.
Energy rich compounds
contains energy rich phosphate bonds or CoA
What do energy rich compounds allow
- making of ATP by transferring phosphate bond to ADP by substrate level phosphorylation
- can produce fatty acids
Redox Balance
balancing number of atoms (reactants and products)
How do protons get reduced to H2 during fermentation
- hydrogenlyase
- hydrogenase
- electron configuration
Alcoholic fermentation
hexose = ethanol + CO2
Homolactic fermentation
hexose = lactate + 2H
Heterolactic fermentation
hexose = lactate + ethanol + H + CO2
Mechanism of homofermmentative lactic acid bacteria
Glucose = 2 lactate + 2H+
- delta G: -196kJ
- yields: 2 ATP
Mechanism of heterofermmentative lactic acid bacteria
Glucose = 2 lactate + ethanol + CO2 + H+
- delta G: -216 kJ
- yields: 1 ATP
Mechanism of mixed acid fermentation
2 pyruvate + NADH = 2 CO2 + butanediol
Mechanism of sugar fermentation by Clostridium
1.5 Glucose + H2O = acetate + butyrate + 3 CO2 + 4H2 + H+
- delta G: -250 kJ
- yields: 3/4 ATP/glucose
Obligate anaerobes
cant tolerate 02, produce H2 from fermentation
Clostridium
- ferment sugars and amino acids
- ATP synthesis through substrate level phosphorylation
- generates proton motive force
Mechanism of Stickland Reaction
Alanine + 2 glycine + 2H2O = 3 acetate + CO2 + 3 NH4+
- delta G: -186kJ
- yields: 3 ATP
Mechanism of energy converting Hydrogenase
Glucose + 2 H2O = 2 acetate + 2CO2 + 4H2 + 2H+
- delta G: -216 kJ
- yields: 4 ATP
Secondary Fermentations
Uses primary fermentations as substrates
Propionibacterium
Can’t produce lactic acid by itself, uses it from fermentation product of lactic acid bacteria
Mechanism of Succinate Fermentation
- succinate is convertd to propinate through decarboxylation of intermediate
- this releases energy by decarboxylation reaction, used to move 2 Na+ across membrane
- Energy is then conserved by using a Na+ - linked ATPase
Syntropy
2 different microbes cooperate to perform metabolic reaction (most secondary fermentations)
What are the two types of electron transfer?
- Direct: two microbes connect
- Mediated: through diffusion (H2)
Interspecies electron transfer
how microbes undergo syntropy. 1 species usually electron donor, the other, electron acceptor
Example of interspecies H2 transfer?
Ethanol fermentation carried out by syntroph has positive free energy so it cant grow in pure culutres
- H2 produced used as electron donor by methanogen to produce methane, the sum of both reactions is exergonic, when cultured both grow.
Oxygenase
catalyzes incorporation of O2 in organic compounds
Dioxygenase
incorporation of both oxygen atoms
Monooxygenase
Incorporation of 1 oxygen atom, the other as H2O
Mechanism of Hydrocarbon metabolism
1- hydrocarbon as n-octane
gets oxygenated
2- alcohol as n-octanol
gets dehydrogenated
3- aldehyde as n-octanal
gets dehydrogenated
4- acid as n-octanoic acid
Importance of aromatic catabolisms?
Everything gets turned to a catechol before being reduced to enter citric acid cycle
