Question

Organisms use different sources of carbon and energy. Archaeans do NOT use glycolysis and do NOT always use the pentose phosphate pathway, but use variations on these pathways for similar purposes. What is the best classification of this type of catabolism?

Choose the best answer.

A. Chemolithotrophs

B. Chemoorganotrophs

C. Photoheterotrophs

D. Photoautotrophs

Answer 1

Archaeans do NOT use glycolysis and do NOT always use the pentose phosphate pathway, but use variations on these pathways for similar purposes. The best classification of this type of catabolism would be B. Chemoorganotrophs .

Most of the archaean use a modified form of glycolysis (the Entner–Doudoroff pathway) and either a complete or partial citric acid cycle. We can have the example of Pyrococcus abyssi.

This is quite an exotic prokaryote, what biologists actually call an extremophile. It belongs to Archaea, the third kingdom of life. It is a hyperthermophile; its optimal growth temperature is 96 degree C. In pyrococci all metabolites of glycolysis are identical to those of humans; the differences concern only the cofactors (Sapra et al. 2003). Pyrococcus uses ADP as phosporyl donor in the first two phosphorylation steps of glycolysis, and instead of NAD+ it uses ferrodoxin and tungsten. Pyruvate is decarboxylated to acetyl-CoA (here again pyrococci use a ferredoxin oxidoreductase). The free energy of the CO2 release reaction is stored in the thioester bond to coenzyme A and is used for the synthesis of a further ATP
with the concomitant release of acetate. The wide phylogenetic and ecological distribution and conservation of glycolysis speaks for one of the oldest sugar degradation pathway invented in biological systems on earth.

Though there are some archaeans who follow lithotropic metabolic pathway. i.e. using inorganic substrate (usually of mineral origin) to obtain reducing equivalents for use in biosynthesis (e.g., carbon dioxide fixation) or energy conservation (i.e., ATP production) via anaerobic respiration. eg. Ferroglobus

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