Carbon metabolism Part 2

Question 1

Electron transfer chain

Answer 1

Takes electrons from NADH with high energy.
Uses energy emitted for the synthesis of ATP.
When electrons have low energy, are used in the formation of water.

Molecules (eg NADH) with more negative reduction potentials will spontaneously donate electrons to molecules with more positive reduction potentials (CO2).

Question 2

Chemiosmosis

Answer 2

Chemiosmosis is the movement of protons across a selectively permeable membrane, down their electrochemical gradient.

More specifically: relates to the generation of ATP by the movement of hydrogen ions across a membrane during cellular respiration.

Question 3

Proton motive force

Answer 3

The difference in chemical concentration and charge gradient across the inner mitochondrial membrane.

Question 4

Facultative anaerobe

Answer 4

Organisms that can grow aerobically and in the absence of oxygen, resort to fermentative metabolism.

Question 5

Fermentation is a type of

Answer 5

metabolism

Question 6

In Fermentation

Answer 6

• Organic molecule is the electron donor and acceptor
• electron acceptor is endogenous
• all ATP is formed only from substrate-level phosphorylation since the electron transport chain does not work

Question 7

No O2 present in the respiration:

Answer 7

ETC does not work, thus cell finds other ways to oxidize the NADH or else glycolysis will stop (needs NAD)
-So organic molecules act as terminal electron acceptors. NADH gets oxidized to NAD and fermentation products are the result. (alcohol/lactate)

Question 8

Why does fermentation work?

Answer 8

NADs are regenerated together with the formation of fermentation products.

Question 9

Different fermentations have

Answer 9

pyruvate as the starting point for fermentation.

Question 10

Ethanol fermentation is done by the yeast

Answer 10

Saccharomyces cerevisiae (brewers yeast)

Question 11

Saccharomyces cerevisiae

Answer 11

• Important microorganism for industrial application
• Baking, brewing, and winemaking industries
• Biofuel production (1st and 2nd gen ethanol)
• primarily regarded as a fermentative microorganism because of its association with ethanol fermentation.
• Can ferment glucose at high ethanol concentrations. (25%)
• Can also utilize glucose through a fully respiratory metabolism.

Question 12

Produces ethanol in the presence of O2

Answer 12

• oxido-reductive metabolism

- respiro-fermentative metabolism

Question 13

Crabtree effect

Answer 13

• S. cerevisiae can produce ethanol in the presence of oxygen (aerobically)
• This happens in the presence of high external glucose concentration and at high growth rates
• It is the incomplete oxidation of glucose. (not all of the hydrogen is removed, with less NADHs going to the ETC and therefore less ATP is produced since a large amount of carbon is diverted away from the central metabolic pathway at pyruvate to form ethanol.

Question 14

When does the crabtree effect take place?

Answer 14

High external glucose concentration and starts above a certain growth rate.
(this property can be exploited in continuos and fed-batch culture)

Question 15

Pasteur effect

Answer 15

fermentation activity of yeast decreases at low glucose concentrations during aeration and an increasing part of the glucose is converted to CO2.

Question 16

with respect to yeast cells: At low glucose concentrations and in the presence of O2

Answer 16

• ethanol production decreases
• Cell biomass yield increase
• more efficient energy generation through ATP from ETC.

Question 17

Where is the crabtree effect used in industry?

Answer 17

The Crabtree effect is used in beer and winemaking.

Question 18

WHere is the Pasteur effect used in industry?

Answer 18

The Pasteur effect is used in the production of baker’s yeast.

Question 19

Modified Krebs cycle

Answer 19

Takes place under fermentative conditions and is known as the glyoxylate pathway.

Question 20

Glyoxylate pathway

Answer 20

An alternative pathway to replenish intermediates that are used during biosynthesis - called anaplerotic pathways or “filling-in pathways”.

Also be used to generate intermediates for biosynthesis when ethanol and acetate are used as carbon sources (i.e. for gluconeogenesis).

Question 21

Pyruvate in the glyoxylate pathway

Answer 21

Oxaloacetate is generated from pyruvate by carboxylase enzymes. (pyruvate not converted to acetyl-CoA by dehydrogenase)

Question 22

Degradation of fatty acids

Answer 22

Also known as beta-oxidation of fats

• aerobic process
• occurs in mitochondrial cytoplasm
• transported across mitochondrial membrane with carrier carnitine
• energy released depends on the length of the fatty acid chain
• breakdown of recalcitrant molecules e.g. alkanes
• can produce polyhydroxylalkanoates (biodegradable plastics) from intermediates

Question 23

Describe the process of degradation of fatty acids

Answer 23

Fatty acids -> beta-oxidation ->

1. energy and intermediates via TCA cycle
2. Glucose via gluconeogenesis

Question 24

Reverse of glycolysis

Answer 24

Called gluconeogenesis