GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Evolutionary Theories

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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Example Questions

Example Question #1 : Help With Evolutionary Theories

Which of the following is not true of the endosymbiotic theory?

Possible Answers:

The inner membrane of mitochondria displays similarities to bacterial membranes

The mitochondria shows similarities to fossilized microorganisms 

None of the answers

Mitochondria have their own genomes that contain similarities to bacterial genomes

Correct answer:

None of the answers

Explanation:

All three of the given answers are true and supportive of the endosymbiotic theory. Because mitochondria have membranes and genomes similar to those contained by bacteria, it is likely that they were once free-living organisms. The mitochondria have also been known to display remarkable similarities to fossilized microorganisms.

Endosymbiotic theory suggests that mitochondria were once free-living prokaryotes that were engulfed by a larger prokaryote. The engulfed cell still generated a proton gradient between its cell membrane and cell wall for energy synthesis, which the larger surrounding cell was able to use. The larger cell provided protection for the engulfed cell. Over time, the engulfed cell lost some of its distinct features, but continued to produce energy, evolving into the modern mitochondrial organelle.

Example Question #2 : Help With Evolutionary Theories

The __________ theory hypothesizes that __________ were originally free-living prokaryotes. 

Possible Answers:

ectosymbiotic . . . mitochondria

ectosymbiotic . . . lysosomes

endosymbiotic . . . mitochondria

endosymbiotic . . . lysosomes

Correct answer:

endosymbiotic . . . mitochondria

Explanation:

Ectosymbiosis is a term that refers to an organism that lives on the outside of the host. Both lysosomes and mitochondria are inside of the cell, so these choices cannot be correct.

The endosymbiotic theory postulates that mitochondria were once free-living prokaryotes that have evolved to form a symbiotic relationship with eukaryotic cells. The original prokaryotes were engulfed by larger prokaryotic cells, but continued to generate energy via the membrane gradient. This energy was used by both the smaller engulfed cell and the larger cell, and the smaller cell gained protection and nutrients. Eventually, this relationship evolved into modern eukaryotic cells and mitochondria. There is a plethora of evidence to support this theory. A few examples are that the mitochondrial membranes are more similar in structure to those of bacteria than of eukaryotes, and mitochondria contain their own genomes. 

Example Question #3 : Help With Evolutionary Theories

Which if the following organelles is not theorized to have arisen in eukaryotes via an endosymbiotic relationship?

Possible Answers:

Ribosomes

Flagella

Chloroplasts

Mitochondria

Correct answer:

Ribosomes

Explanation:

The endosymbiotic theory states that ancient prokaryotes may have had a symbiotic relationship with early eukaryotes, leading them to become permanent organelles in the eukaryote. Chloroplasts, mitochondria, and flagella have all been tied to this theory. Ribosomes, however, are organelles found in both prokaryotes and eukaryotes, so they are not a part of the theory.

Example Question #4 : Help With Evolutionary Theories

Which of the following statements is false concerning mitochondria?

Possible Answers:

Mitochondria code for their own ribosomes that resemble bacterial ones

Mitochondria are surrounded with a thin peptidoglycan layer

Mitochondria contain a small circular genome that is separate from the cellular genome

Mitochondria divided separately from the rest of the cell by binary fission

The outer membrane of mitochondria contain porins

Correct answer:

Mitochondria are surrounded with a thin peptidoglycan layer

Explanation:

The endosymbotic theory suggests that mitochondria originated from a bacteria that was engulfed by a proto-eukaryotic cell. Much evidence for this theory is based on the fact that mitochondria resemble bacteria in many ways. They do not however contain a peptidoglycan cell wall like almost all bacterial cells do.

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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