Evolution connection: The Krebs CycleEvolution connection: The Krebs Cycle

Learning goals:

Students will understand that 1) the uniformity of the Krebs cycle reactions across all life is due to

inheritance from a common ancestor, 2) different lineages have evolved slight variations in the

Krebs cycle reactions as they have diverged, and 3) the eukaryotic version of the Krebs cycle

actually comes from the endosymbiotic bacterium from which our mitochondria evolved.

For the instructor:

This short slide set explains the uniformity of the Krebs cycle across all life using evolutionary

theory. To integrate it best, use these slides immediately after you’ve discussed aerobic respiration.

Each of the following slides comes with a sample script for the instructor.  To review this script,

download the PowerPoint file and view the Notes associated with each slide .

Evolution Connection slideshows are provided by Understanding Evolution

(understandingevolution.org) and are copyright 2011 by The University of California Museum of

Paleontology, Berkeley, and the Regents of the University of California. Feel free to use and modify

this presentation for educational purposes.

Evolution connection: The Krebs CycleEvolution connection: The Krebs Cycle

“That’s a lot of reactions. How many of these metabolicpathways do we need to memorize?”

Not many … why?

Because most organisms you’re familiar with (aerobicones) use the Krebs Cycle, electron transport chain, andoxidative phosphorylation. There’s just one set ofreactions to worry about for them.

Heliobacter pylori photo by Yutaka Tsutsumi, M.D. Professor Department of Pathology Fujita Health University School of Medicine; Blue-green

algae photo by Micrographica.com; Redwood and mountain lion photos by Gerald and Buff Corsi © California Academy of Sciences; Oyster

mushroom photo by Dr. Robert Thomas and Dorothy B. Orr © California Academy of Sciences.

But why?

Because these metabolic pathways evolved early inthe history of life and were passed on to many differentlineages.

Aerobic metabolism evolves!

Evolution connection: The Krebs CycleEvolution connection: The Krebs Cycle

Heliobacter pylori photo by Yutaka Tsutsumi, M.D. Professor Department of Pathology Fujita Health University School of Medicine; Blue-green

algae photo by Micrographica.com; Redwood and mountain lion photos by Gerald and Buff Corsi © California Academy of Sciences; Oyster

mushroom photo by Dr. Robert Thomas and Dorothy B. Orr © California Academy of Sciences.

These reactions work pretty much the same wayin you, birds, bees, many bacteria, and tons ofother critters!

Evolution connection: The Krebs CycleEvolution connection: The Krebs Cycle

The evolution of the Krebs cycle:

Archaea

Bacteria

Eukaryotes

Evolution connection: The Krebs CycleEvolution connection: The Krebs Cycle

Where did our (eukaryotic) versionof the Krebs cyclecome from?

UsRickettsia

bacterium

Evolution connection: The Krebs CycleEvolution connection: The Krebs Cycle

References:References:

Andersson, S. G. E, et al. 1998. The genome sequence of Rickettsia

prowazekii and the origin of mitochondria. Nature. 396: 133-140.

Huynen, M. A., Dandekar, T., and Bork, P. 1999. Variation and evolution

of the citric acid cycle: a genomic perspective. Trends in Mircrobiology.

7: 281-291.

Evolution Connection slideshows are provided by Understanding Evolution

(understandingevolution.org) and are copyright 2011 by The University of California

Museum of Paleontology, Berkeley, and the Regents of the University of California.

Feel free to use and modify this presentation for educational purposes.