Question

(a) Explain why obligate anaerobes contain some citric acid cycle enzymes. (b) Why don’t these organisms have a complete citric acid cycle?

Short answer

Answer

(a) Anaerobes must be able to produce citric acid cycle intermediates such as citrate and succinyl-CoA since they are precursors for the production of other chemicals

(b) Obligate anaerobes don’t have a complete citric acid cycle because the citric acid cycle is not needed for anaerobic organisms, and would waste energy by regenerating coenzymes

Step-by-step solution

Obligate anaerobes

Obligate anaerobes are microorganisms killed by normal atmospheric concentrations of oxygen (20.95% O₂). Obligate anaerobes, which can only live in the absence of oxygen, lack the defenses that allow aerobic life and hence cannot survive in the presence of oxygen

Reason for obligate anaerobes contain some citric acid cycle enzymes  

(a)Obligate anaerobes are microorganisms killedthroughregularatmospheric concentrations of oxygen (20.95% O2). Oxygen tolerance variesamongspecies, witha fewspeciesable tosurvive inas much as8% oxygen,at the same time asothers lose viability in environments with an oxygenawarenessofmorethan 0.5%

Because intermediates such as citric acid are present in obligatory anaerobes, they have some citric acid cycle enzymes Precursors for the production of other molecules such as proteins, carbohydrates, and lipids include oxaloacetate, malate, and fumarate.

Other purposes of citric acid cycle enzymes 

Thepredominantfunctionsof the citric acid cycle are: A) synthesis of citrate and gluconeogenesis. B) degradation of acetyl-CoAto supplystrengthand todeliverprecursors for anabolism.

The function of the citric acid cycle is to harvest electrons from carbon compounds to produce energy. The other function is to produce intermediates. Acetyl-CoA breakdown generates energy and provides anabolism precursors.

The name citric acid cycle comes from the first product produced by

the conversion process, which is citric acid.

Step 3: Reason why don’t obligate anaerobes to have a complete citric acid cycle

(b)Anaerobes get their energy from anoxygenic fermentation where the end products are some alcohols and/or some organic acids.They obtain free energy through routes that are independent of those that oxidize carbon-containing molecules. A process like this is impossible in an organism that has its aerobic system turned on or can't thrive in anoxygenic settings

In eukaryotes, it is in the mitochondria, and in prokaryotes where mitochondria do not exist, it is on the invaginations of plasma membranes.

These organisms do not utilize all of the citric acid cycle enzymes to make reduced cofactors, which are then oxidized by molecular oxygen.