Fermentation

Question 1

What is the difference between Fermentation and respiration?

Answer 1

• 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

Question 2

What is substrate level phosphorylation?

Answer 2

directly phosphorylating ADP with a phosphate and energy provided from a coupled reaction

Question 3

What is required or not required in substrate level phosphorylation?

Answer 3

• 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)

Question 4

What is electron transport phosphorylation?

Answer 4

• 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

Question 5

What are the advantages of fermentation?

Answer 5

• lack of oxygen or other electron acceptors
• absence of Fe
• faster throughput and generation of ATP growth

Question 6

What are the disadvantages of fermentation?

Answer 6

• lot less ATP produced

Question 7

What is fermentation?

Answer 7

the chemical breakdown of a substance by bacteria, yeasts, or other microorganisms, not using an external electron acceptor

Question 8

What are the advantages of respiration?

Answer 8

• usually much higher ATP yield (depends on redox potential of e- acceptor)

Question 9

What are the disadvantages of respiration?

Answer 9

• longer metabolic pathway can make respiration slower
• needs electron acceptor
• needs Fe for cytochromes, FeS

Question 10

What is respiration?

Answer 10

Oxidation of a substrate that is coupled to reduction of external electron acceptor

Question 11

What is the solution for how during fermentation you cannot get rid of electrons?

Answer 11

• oxidise one part of the substrate and reduce another

- can make extra ATP if can get rid of electrons as H2

Question 12

Go over the pathway of ethanol fermentation by yeast.

Answer 12

1. glycolysis occurs to produce pyruvate
2. pyruvate becomes decarboxylated to generate acetaldehyde
3. Acetaldehyde is reduced to ethanol

Question 13

What are the products of ethanol fermentation in yeast?

Answer 13

• carbon dioxide (oxidised)

- ethanol (reduced)

Question 14

How does Zymomonas mobilis (bacterium) bypass the whole glycolysis step and create the pyruvate able to be fermented into ethanol?

Answer 14

• oxidises glucose-6-phosphate

- splitting the oxidised product into G3P and pyruvate

Question 15

How much ATP is made using the EMP pathway that yeast uses for glucose fermentation?

Answer 15

2 ATP

Question 16

How much ATP is made using the EDP pathway that bacterium uses for glucose fermentation?

Answer 16

1 ATP

Question 17

Why does the bacterium not use the EMP pathway that yeast does?

Answer 17

• it can grow as quickly as yeast due to the pathway being shorter
• rate of ATP is therefore as good as yeast

Question 18

Go over the pathway of fermentation by Ruminococcus.

Answer 18

1. glycolysis occurs to produce pyruvate
2. NADH produced from pyruvate can be reduced to produce hydrogen
   - hydrogen conc needs to be kept low enough for this reaction to take place
3. 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)

Question 19

How can you get 4ATP out of fermenting glucose in Ruminoccous albus?

Answer 19

• get rid of electrons as hydrogens
• oxidise all carbon to acetate and CO2
• 1 ATP for every acetate made
• reduce production of ethanol

Question 20

How do you transfer electrons from NADH to H2?

Answer 20

• 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

Question 21

What do hydrogenase enzymes do? Link to structure

Answer 21

• reduces protons to form hydrogens
• 2H+ + 2e- —-> H2
• contains Ni
• some are proton pumps and are similar to complex 1

Question 22

What are the different mechanisms that can generate ATP?

Answer 22

• 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