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.
