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One Cell, Three Genomes Laboratory

Background

In high school you probably learned that the nucleus, chloroplast, and mitochondrian came into existence through endosymbiotic events— i.e., that one cell engulfed two others and now the three cells rely on each other for survival as a single plant cell. This lab is designed to let you test this hypothesis.

Chloroplasts are only found in eukaryotic algae, leaves and other green plant organs. They are the photosynthetic organelles in plants that harvest light energy and convert it to chemical energy for growth and other vital functions. The chloroplasts do not produce energy for (ATPs) the cell, however. Through the process of photosynthesis, they produce the raw materials that the mitochondria use in the process of cellular respiration.

Mitochondria, on the other hand, are found in almost all eukaryotic cells. Not only are they much more efficient at generating ATP that are the fermentation pathways in the cytosol, by uncoupling or coupling electron transport from oxidative phosphorylation, they are the primary regulator of heat productionin cells.

Nuclear DNA refers to the DNA that has become trapped within the nucleus of eukaryotic cells. This is one of the defining features separating prokaryotic organisms from eukaryotic organisms.

Data

None provided. Choose a model system (i.e. RNA or protein) and search the databases for these sequences.. There are several databases on organelles that you might consider visiting.

Tools

Biology Workbench (http://workbench.sdsc.edu -- the San Diego one).
Note: Select to search ONLY the organelle database

GeneDoc (locally installed)

If network access is interrupted, please use the locally installed versions of

Phylip and ClustalX in place of Biology Workbench

Potential Investigations

Session I

    • Has any organelle (chloroplast or mitochondrial) DNA "jumped" to the nuclear DNA in evolutionary history?
    • If both mitochondria and chloroplasts evolved from prokaryotic cells, have they retained any of the features of the prokaryotic cells from which they evolved?

Session II

    • Can you find any primitive eukaryotic cells that are devoid of these organelles— either chloroplasts or mitochondria? Where do they branch off from a tree of all eukaryotes?
    • Is it feasible to consider that a bacterium was once "ingested" by a primative eukaryotic cell such that the bacterium became symbiotic?
    • Do the genes located in the organelle genomes change at the same rate as the nuclear DNA (i.e. do they all use the same molecular clock)?
    • Has there been horizontal gene transfer between mitochondria and chloroplasts?
    • Relate your investigation of transfer of genes between organelles over evolutionary time with published models of protein trafficking between organelles over the course of the lifetime of a single live cell.

Goals

Session I

    • Identify definable questions that can be approached using phylogenetics
    • Find the data & use the tools provided to explore these questions
    • Share your insights with the group

Session II

    • Using your results from Session I, design and execute experiments to approach these larger questions
    • Using the your analyses, the data & tools provided explore these questions
    • Share your insights with the group
    • Evaluate the effectiveness of this exercise and these two sessions.

 

 
 
Authors: Sam Donovan, John Greenler, John Jungck -- 2002