Giardia intestinalis is an intestinal parasite of humans and other mammals that causes intestinal ailments in most people who ingest the cysts. Upon ingestion, each cyst releases two motile cells, called "trophozoites". These attach to the small intestine's lining via a ventral adhesive disk. The trophozoites anaerobically metabolise glucose from the host's intestinal contents to produce ATP. Reproduction is completely asexual, occurring by longitudinal binary fission of trophozoites, with each daughter cell receiving two haploid nuclei (n = 5). A trophozoite will often encyst as it passes into the large intestine by secreting around itself a case that is resistant to cold, heat, and dehydration. Infection usually occurs by drinking untreated water that contains cysts.
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The mitosome of Giardia has no DNA within it. If it did contain DNA, then what predictions should we be able to make about its DNA?
A) It is linear, has many introns, and is not associated with histone proteins.
B) It is linear, has few introns, and is complexed with histone proteins.
C) It is circular, has many introns, and is complexed with histone proteins.
D) It is circular, has few introns, and is not associated with histone proteins.

Question

Quizplus · Accepted Answer

The absence of DNA in the mitosome suggests that it may be a highly reduced form of mitochondria. Mitochondria have circular DNA with few introns and are not associated with histone proteins. Therefore, if the mitosome of Giardia contained DNA, it would likely have a similar structure, with circular DNA, few introns, and no association with histone proteins. Choice D is the only option that matches these predictions.

Giardia Intestinalis Is an Intestinal Parasite of Humans and Other