Fermentation

Question 1

Do most bacteria rely on fermentation alone?

Answer 1

No, most have some other pathway available and only use fermentation as a last resort

Question 2

How do Lactobacillus species survive using only fermentation?

Answer 2

They live in a sugar-rich environment, so they’re fine

Question 3

Why is fermentation the worst option for energy production?

Answer 3

ATP is only made by substrate-level phosphorylation, so only get a little bit of energy

Question 4

What are the end products of fermentation?

Answer 4

Organic molecules that are secreted from the cell as metabolic waste

Question 5

What is the terminal electron acceptor of fermentation?

Answer 5

Organic metabolic intermediates

Question 6

Why is fermentation so wasteful?

Answer 6

The end products still have a ton of energy that is inaccessible if the cell is only doing fermentation

Question 7

How is a fermentation pathway named?

Answer 7

After the end product

Question 8

What is the point of fermentation?

Answer 8

Recycle NADH to keep doing glycolysis

Question 9

Why does the cell need to recycle NADH through fermentation?

Answer 9

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

Question 10

How does fermentation recycle NADH?

Answer 10

Takes the high energy electrons from NADH and puts them on an organic waste molecule that is excreted

Question 11

What is the start and end products of ethanolic fermentation?

Answer 11

Pyruvate from glycolysis is converted to ethanol and CO2

Question 12

What are the two reactions in ethanolic fermentation?

Answer 12

Pyruvate to acetylaldehyde + 2 CO2, then acetyaldehyde to ethanol

Question 13

What is the end product in ethanolic fermentation?

Answer 13

Ethanol and CO2

Question 14

What is the terminal electron acceptor in ethanolic fermentation?

Answer 14

Acetaldehyde

Question 15

How many ATP get produced by ethanolic fermentation?

Answer 15

2 (from glycolysis)

Question 16

How do we apply ethanolic fermentation for our own purposes?

Answer 16

Brewing and bread making

Question 17

What are the start and end products of homolactic fermentation?

Answer 17

Starts with pyruvate, ends with lactic acid

Question 18

How many ATP get produced per glucose by homolactic fermentation?

Answer 18

2

Question 19

What is the terminal electron acceptor of homolactic fermentation?

Answer 19

Pyruvate

Question 20

How do we apply homolactic fermentation for our own purposes?

Answer 20

Cheese, yogurt, sauerkraut

Question 21

What are the start and end products of heterolactic fermentation?

Answer 21

Starts with pyruvate and acetyl-phosphate and ends with ethanol and lactic acid

Question 22

How many ATP get produced by heterolactic fermentation?

Answer 22

1

Question 23

Why does heterolactic fermentation produce less ATP than other fermentation pathways?

Answer 23

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

Question 24

What are the terminal electron acceptors of heterolactic fermentation?

Answer 24

Pyruvate, acetaldehyde, acetyl phosphate

Question 25

How do we use heterolactic fermentation for our own purposes?

Answer 25

Sourdough bread, kimchi, sauerkraut

Question 26

What are the start and end products of mixed acid fermentation?

Answer 26

Starts with pyruvate and produces formate, lactate, ethanol, acetate, succcinate, CO2 and H2

Question 27

How many ATP get produced during mixed acid fermentation?

Answer 27

2

Question 28

What are the terminal electron acceptors of mixed acid fermentation?

Answer 28

Pyruvate, acetyl-CoA, acetaldehyde, fumarate, oxaloacetate

Question 29

What are the start and end products of butanediol fermentation?

Answer 29

Starts with pyruvate ends with mostly butanediol, a little bit of acid, a lot of CO2 and a little bit of H2

Question 30

How many ATP get produced by butanediol fermentation?

Answer 30

2

Question 31

What is the terminal electron acceptor in butanediol fermentation?

Answer 31

Acetoin

Question 32

What are the 2 differences between mixed acid and butanediol fermentation?

Answer 32

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

Question 33

What test can you run on enteric bacteria to determine if they’re using mixed acid or butanediol fermentation?

Answer 33

MRVP test. The MR test detects acid and the VP test detects acetoin

Question 34

Does fermentation generate a proton motive force?

Answer 34

No, only ATP

Question 35

How do cells generate the PMF when they’re using fermentation?

Answer 35

ATP synthase runs backwards. It hydrolyzes an ATP to pump 4 protons out and generate the PMF

Question 36

What are the steps in cheese making?

Answer 36

1. Pasteurization of the milk
2. Add bacteria that do homolactic fermentation
3. Add rennet
4. Remove the whey with filtration
5. Add salt
6. Press curds into a shaping mold
7. Secondary fermentation

Question 37

Why are bacteria that do homolactic fermentation added to the pasteurized milk to make cheese?

Answer 37

The fermentation will break down the lactose into lactic acid, which causes the milk to curdle from the low pH

Question 38

What is rennet?

Answer 38

An enzyme that partially breaks down casein and causes the proteins to form big clumps (curds)

Question 39

What is secondary fermentation in cheese making?

Answer 39

Adding a different species of bacteria that does different kinds of fermentation to the curds to produce a bunch of different cheeses