Carbon metabolism Part 2 Flashcards
Electron transfer chain
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).
Chemiosmosis
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.
Proton motive force
The difference in chemical concentration and charge gradient across the inner mitochondrial membrane.
Facultative anaerobe
Organisms that can grow aerobically and in the absence of oxygen, resort to fermentative metabolism.
Fermentation is a type of
metabolism
In Fermentation
- 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
No O2 present in the respiration:
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)
Why does fermentation work?
NADs are regenerated together with the formation of fermentation products.
Different fermentations have
pyruvate as the starting point for fermentation.
Ethanol fermentation is done by the yeast
Saccharomyces cerevisiae (brewers yeast)
Saccharomyces cerevisiae
- 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.
Produces ethanol in the presence of O2
- oxido-reductive metabolism
- respiro-fermentative metabolism
Crabtree effect
- 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.
When does the crabtree effect take place?
High external glucose concentration and starts above a certain growth rate.
(this property can be exploited in continuos and fed-batch culture)
Pasteur effect
fermentation activity of yeast decreases at low glucose concentrations during aeration and an increasing part of the glucose is converted to CO2.
with respect to yeast cells: At low glucose concentrations and in the presence of O2
- ethanol production decreases
- Cell biomass yield increase
- more efficient energy generation through ATP from ETC.
Where is the crabtree effect used in industry?
The Crabtree effect is used in beer and winemaking.
WHere is the Pasteur effect used in industry?
The Pasteur effect is used in the production of baker’s yeast.
Modified Krebs cycle
Takes place under fermentative conditions and is known as the glyoxylate pathway.
Glyoxylate pathway
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).
Pyruvate in the glyoxylate pathway
Oxaloacetate is generated from pyruvate by carboxylase enzymes. (pyruvate not converted to acetyl-CoA by dehydrogenase)
Degradation of fatty acids
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
Describe the process of degradation of fatty acids
Fatty acids -> beta-oxidation ->
- energy and intermediates via TCA cycle
- Glucose via gluconeogenesis
Reverse of glycolysis
Called gluconeogenesis
