Carbon Fixation Pathways Quiz

The reductive TCA cycle is a carbon fixation pathway that operates in:

• Aerobic organisms

• Anaerobic and microaerophilic bacteria

• Thermophilic archaea only

• Plants and algae

Which key enzyme reverses the TCA cycle’s citrate synthase step in the reductive TCA cycle?

• ATP-citrate lyase

• Malate dehydrogenase

• Isocitrate dehydrogenase

• Succinyl-CoA synthetase

Which intermediate is directly fixed into organic molecules in the reductive TCA cycle?

• Acetyl-CoA

• Oxaloacetate

• Succinyl-CoA

• 2-Oxoglutarate

The reductive TCA cycle is used by:

• Sulfate-reducing bacteria and some archaea

• Cyanobacteria

• Methanogenic archaea

• Fungi

Which reducing agent is essential for the reductive TCA cycle?

• NADPH

• NADH

• FADH2

• Both NADH and FADH2

How does the reductive TCA cycle conserve energy during carbon fixation?

• Through ATP generation

• By coupling with chemiosmotic gradients

• By reducing intermediates with minimal ATP consumption

• Using light energy

In the reductive TCA cycle, succinyl-CoA is converted into:

• Oxaloacetate

• Alpha-ketoglutarate

• Malate

• Citrate

The key enzyme ferredoxin oxidoreductase in the reductive TCA cycle requires:

• FAD

• Ferredoxin

• Biotin

• Coenzyme A

What is the role of fumarate reductase in the reductive TCA cycle?

• Reduces fumarate to succinate

• Oxidizes succinate to fumarate

• Converts fumarate to malate

• Generates NADPH

The reductive TCA cycle is considered:

• An ancient autotrophic pathway

• A derivative of the glycolytic pathway

• Limited to aerobic organisms

• An inefficient carbon fixation process