22 - Catabolism Flashcards
Fuel molecule
high energy molecules with energy stored in chemical bonds (e.g. glucose)
Glycolysis
Conversion of glucose to pyruvate.
TCA cycle
Conversion of pyruvate to CO2
what do all organisms require
- Energy to make ATP
- Electron source to make ATP
- Carbon source to synthesise molecules
Catabolism
- Larger, more complex molecules are broken down into smaller, simpler molecules with the release of energy
- Fuelling reactions supply ATP, reducing power, and precursor metabolites
Anabolism
The synthesis of more complex molecules from simpler ones, with the input of energy
Important electron carrier pairs involved in catabolism
- NAD+
- FAD
- Ubiquinone (coenzyme Q), flavoproteins, cytochromes
Why is ATP a high energy molecule
Because of the energy required to maintain the bonds between the bulky, negatively charged phosphate groups
What is the link between catabolism and anabolism
ATP
3 types of catabolism in chemoorganotrophs
- Aerobic respiration (O2 as electron acceptor)
- Anaerobic respiration (non O2 compound as electron acceptor)
- Fermentation (Using organic compounds as electron acceptor)
3 steps of glucose catabolism
- Glycolysis (glucose –> pyruvate, produces ATP and NADH)
- TCA (Krebs) cycle (pyruvate –> CO2, produces ATP, NADH and FADH2)
- Electron transport chain (NADH, FADH2 –> ATP, O2 is terminal electron acceptor)
3 major pathways of Glycolysis
- Embden-Meyerhof pathway
- Pentose phosphate pathway
- Entner-Doudoroff pathway
Embden-Meyerhof pathway
- Most common
- Occurs in all major groups of microbes
- Functions in the presence or absence of O2
Pentose phosphate pathway
-Alternative/complementary pathway for producing glycolysis intermediates
- Most microbes have this
Entner-Doudoroff pathway
- Some Gram-negative bacteria (e.g. Pseudomonas, Rhizobium)
- Not used by eukaryotes of most Gram-positives
How are electrons harvested
NAD and FAD form redox pairs with fuel molecules during fuel molecule catabolism
Harvesting electrons as reducing power example
NAD+ acquires reducing power when it reacts with malate in the TCA cycle. Malate is oxidised (loses electron) and NAD+ is reduced (gains electron)
4 step process of ATP being synthesised by oxidative phosphorylation
- Electrons harvested by electron carriers during fuel molecule degradation enter an ETC
- Passage of electrons through the ETC by a series of interlinked electron carrier pairs
- Generation of a proton motive force from the electron transport chain
- Formation of ATP using the proton motive force by ATP Synthase
What determines free energy released in ETC
The difference in reduction potential between the electron carrier redox pair and the terminal
electron acceptor redox pair
ATP yield of glycolysis (substrate level
phosphorylation)
2
ATP yield of TCA cycle (substrate level
phosphorylation)
2
ATP yield of ETC (oxidative phosphorylation)
28 (7 times more than substrate level)
Total ATP yield (in eukaryotes) during aerobic respiration
32
Why does anaerobic respiration yield less energy
As the standard reduction potential is less positive than for O2
Dissimilatory nitrate reduction
Use of nitrate as a terminal electron acceptor makes it unavailable for other uses
Denitrification
Reduction of nitrate to nitrogen gas causes a loss of soil fertility
Fermentation
Pyruvate acts as an electron acceptor, which:
- Regenerates NAD+ (requirement for maintenance of glycolysis)
- Ensures ATP formation by SLP is maintained
- Produces a variety of fermentation byproducts
Types of lactic acid fermentation
Homolactic and heterolactic
Homolactic
Mostly lactate produced
Heterolactic
Lactate + ethanol + CO2
Types of fermentation
- Lactic acid fermentation
- Alcohol fermentation (ethanol)
- Mixed acid (lactate)
– Butanediol
How much energy does fermentation yield
only yields ATP by substrate level phosphorylation.
Produces 2 ATP per molecule of glucose (compared to 32 ATP by aerobic respiration).
Therefore microbial growth much slower
What delivers electrons to ETC
NADH and FADH2
