Fermentation Flashcards
Do most bacteria rely on fermentation alone?
No, most have some other pathway available and only use fermentation as a last resort
How do Lactobacillus species survive using only fermentation?
They live in a sugar-rich environment, so they’re fine
Why is fermentation the worst option for energy production?
ATP is only made by substrate-level phosphorylation, so only get a little bit of energy
What are the end products of fermentation?
Organic molecules that are secreted from the cell as metabolic waste
What is the terminal electron acceptor of fermentation?
Organic metabolic intermediates
Why is fermentation so wasteful?
The end products still have a ton of energy that is inaccessible if the cell is only doing fermentation
How is a fermentation pathway named?
After the end product
What is the point of fermentation?
Recycle NADH to keep doing glycolysis
Why does the cell need to recycle NADH through fermentation?
There is a finite amount of NAD+ in cells and you can’t put electrons into NADH, so if it doesn’t get recycled, glycolysis stops and the cell can’t produce energy and dies
How does fermentation recycle NADH?
Takes the high energy electrons from NADH and puts them on an organic waste molecule that is excreted
What is the start and end products of ethanolic fermentation?
Pyruvate from glycolysis is converted to ethanol and CO2
What are the two reactions in ethanolic fermentation?
Pyruvate to acetylaldehyde + 2 CO2, then acetyaldehyde to ethanol
What is the end product in ethanolic fermentation?
Ethanol and CO2
What is the terminal electron acceptor in ethanolic fermentation?
Acetaldehyde
How many ATP get produced by ethanolic fermentation?
2 (from glycolysis)
How do we apply ethanolic fermentation for our own purposes?
Brewing and bread making
What are the start and end products of homolactic fermentation?
Starts with pyruvate, ends with lactic acid
How many ATP get produced per glucose by homolactic fermentation?
2
What is the terminal electron acceptor of homolactic fermentation?
Pyruvate
How do we apply homolactic fermentation for our own purposes?
Cheese, yogurt, sauerkraut
What are the start and end products of heterolactic fermentation?
Starts with pyruvate and acetyl-phosphate and ends with ethanol and lactic acid
How many ATP get produced by heterolactic fermentation?
1
Why does heterolactic fermentation produce less ATP than other fermentation pathways?
These bacteria are missing aldolase, so they can only produce 1 G3P from glucose. The other thing gets sent down the pentose phosphate pathway and is converted into acetyl-phosphate
What are the terminal electron acceptors of heterolactic fermentation?
Pyruvate, acetaldehyde, acetyl phosphate
How do we use heterolactic fermentation for our own purposes?
Sourdough bread, kimchi, sauerkraut
What are the start and end products of mixed acid fermentation?
Starts with pyruvate and produces formate, lactate, ethanol, acetate, succcinate, CO2 and H2
How many ATP get produced during mixed acid fermentation?
2
What are the terminal electron acceptors of mixed acid fermentation?
Pyruvate, acetyl-CoA, acetaldehyde, fumarate, oxaloacetate
What are the start and end products of butanediol fermentation?
Starts with pyruvate ends with mostly butanediol, a little bit of acid, a lot of CO2 and a little bit of H2
How many ATP get produced by butanediol fermentation?
2
What is the terminal electron acceptor in butanediol fermentation?
Acetoin
What are the 2 differences between mixed acid and butanediol fermentation?
Mixed acid produces a ton of acids and CO2 and H2 in equal amounts, while butanediol produces mostly neutral butanediol and lots of CO2 and a little bit of H2
What test can you run on enteric bacteria to determine if they’re using mixed acid or butanediol fermentation?
MRVP test. The MR test detects acid and the VP test detects acetoin
Does fermentation generate a proton motive force?
No, only ATP
How do cells generate the PMF when they’re using fermentation?
ATP synthase runs backwards. It hydrolyzes an ATP to pump 4 protons out and generate the PMF
What are the steps in cheese making?
- Pasteurization of the milk
- Add bacteria that do homolactic fermentation
- Add rennet
- Remove the whey with filtration
- Add salt
- Press curds into a shaping mold
- Secondary fermentation
Why are bacteria that do homolactic fermentation added to the pasteurized milk to make cheese?
The fermentation will break down the lactose into lactic acid, which causes the milk to curdle from the low pH
What is rennet?
An enzyme that partially breaks down casein and causes the proteins to form big clumps (curds)
What is secondary fermentation in cheese making?
Adding a different species of bacteria that does different kinds of fermentation to the curds to produce a bunch of different cheeses
