Fermentation Flashcards
What is the difference between Fermentation and respiration?
- fermentation has a lower ATP yield
- no external electron acceptor therefore substrate has to be reduced and oxidised at the same time (redox disproportionation)
- Electrons gained by the oxidation of the substrate is used to reduce another part of the substrate
What is substrate level phosphorylation?
directly phosphorylating ADP with a phosphate and energy provided from a coupled reaction
What is required or not required in substrate level phosphorylation?
- no membrane required
- no Fe required
- can make exactly 1 ATP
(excess delta G cant be used) (energy quantum is exactly 1 ATP) - only few reactions can be used (oxidative decarboxylation in glycolysis)
What is electron transport phosphorylation?
- happens in respiration and fermentation
- need electron transport chain from electron donor to electron acceptor
- produces a proton or sodium motive force
- needs membrane to establish conc gradient
- have smaller energy quanta
What are the advantages of fermentation?
- lack of oxygen or other electron acceptors
- absence of Fe
- faster throughput and generation of ATP growth
What are the disadvantages of fermentation?
- lot less ATP produced
What is fermentation?
the chemical breakdown of a substance by bacteria, yeasts, or other microorganisms, not using an external electron acceptor
What are the advantages of respiration?
- usually much higher ATP yield (depends on redox potential of e- acceptor)
What are the disadvantages of respiration?
- longer metabolic pathway can make respiration slower
- needs electron acceptor
- needs Fe for cytochromes, FeS
What is respiration?
Oxidation of a substrate that is coupled to reduction of external electron acceptor
What is the solution for how during fermentation you cannot get rid of electrons?
- oxidise one part of the substrate and reduce another
- can make extra ATP if can get rid of electrons as H2
Go over the pathway of ethanol fermentation by yeast.
- glycolysis occurs to produce pyruvate
- pyruvate becomes decarboxylated to generate acetaldehyde
- Acetaldehyde is reduced to ethanol
What are the products of ethanol fermentation in yeast?
- carbon dioxide (oxidised)
- ethanol (reduced)
How does Zymomonas mobilis (bacterium) bypass the whole glycolysis step and create the pyruvate able to be fermented into ethanol?
- oxidises glucose-6-phosphate
- splitting the oxidised product into G3P and pyruvate
How much ATP is made using the EMP pathway that yeast uses for glucose fermentation?
2 ATP
How much ATP is made using the EDP pathway that bacterium uses for glucose fermentation?
1 ATP
Why does the bacterium not use the EMP pathway that yeast does?
- it can grow as quickly as yeast due to the pathway being shorter
- rate of ATP is therefore as good as yeast
Go over the pathway of fermentation by Ruminococcus.
- glycolysis occurs to produce pyruvate
- NADH produced from pyruvate can be reduced to produce hydrogen
- hydrogen conc needs to be kept low enough for this reaction to take place - Pyruvate becomes decarboxylated to Acetyl-CoA
BRANCHED (one oxidated and one reduced branch)
one branch produces ethanol from acetyl coA to acetaldehyde to ethanol
- this branch is used if NADH was not reduced in the previous step to H2.
another branch produces acetate from acetyl coA to acetyl-P to acetate
- this branch used if NADH was reduced in previous step
- this branch also produces ATP (oxidated branch)
How can you get 4ATP out of fermenting glucose in Ruminoccous albus?
- get rid of electrons as hydrogens
- oxidise all carbon to acetate and CO2
- 1 ATP for every acetate made
- reduce production of ethanol
How do you transfer electrons from NADH to H2?
- transfer electrons from NADh to reduce Ferredoxin (Fd)
- replace NAD+ with Fd in the pyruvate decarboxylation step so its pyruvate:Fd not pyruvate-DH
- use hydrogenase to produce H2 from reduced Fdred
What do hydrogenase enzymes do? Link to structure
- reduces protons to form hydrogens
- 2H+ + 2e- —-> H2
- contains Ni
- some are proton pumps and are similar to complex 1
What are the different mechanisms that can generate ATP?
- sodium motive force (decarboxylation driven Na+ pump, Na+ driven ATP synthase)
- light driven proton pump
- product efflux couple proton translocation (lactic acid fermentation)
- flavin based electron bifurcation
