A mutant haploid strain of Saccharomyces cerevisiae(yeast) called cox2-1 was found that was unable togrow on media containing glycerol as the sole sourceof carbon and energy. (Glycerol is a nonfermentablesubstrate for yeast.) This strain could, however, growon the fermentable substrate glucose. Researchers discovered that cox2-1 cells lack a mitochondrial proteincalled cytochrome c oxidase.a. Explain why cox2-1 cells can grow on mediumcontaining glucose but not on glycerol medium.b. When cox2-1 was crossed with a wild-type yeaststrain and the resultant diploid cells were allowedto grow mitotically, it was found that about half thediploid clones were able to grow on glycerol, whilethe other half could not. The diploid clones thatcould grow on glycerol were induced to sporulate,and they yielded tetrads with four spores that wereall able to grow on glycerol medium. In all of thesetetrads, two of the haploid progeny were of matingtype a and two of mating type α. The diploids thatcould not grow on glycerol could not sporulate.What do the results of the mating say about the location of the cox2-1 mutation?c. A different mutant strain of yeast called pet111-1is also unable to grow on glycerol medium but stillcan grow on glucose medium. These mutant cellssimilarly lacked the cytochrome c oxidase. Whenpet111-1 was crossed with a wild-type haploidstrain of the opposite mating type, the resultantdiploids were able to grow on glycerol and yieldedasci that all showed a 2:2 segregation of haploidcells that could or could not grow on glycerol.Explain these results in light of your answer topart (b).
A mutant haploid strain of Saccharomyces cerevisiae
(yeast) called cox2-1 was found that was unable to
grow on media containing glycerol as the sole source
of carbon and energy. (Glycerol is a nonfermentable
substrate for yeast.) This strain could, however, grow
on the fermentable substrate glucose. Researchers discovered that cox2-1 cells lack a mitochondrial protein
called cytochrome c oxidase.
a. Explain why cox2-1 cells can grow on medium
containing glucose but not on glycerol medium.b. When cox2-1 was crossed with a wild-type yeast
strain and the resultant diploid cells were allowed
to grow mitotically, it was found that about half the
diploid clones were able to grow on glycerol, while
the other half could not. The diploid clones that
could grow on glycerol were induced to sporulate,
and they yielded tetrads with four spores that were
all able to grow on glycerol medium. In all of these
tetrads, two of the haploid progeny were of mating
type a and two of mating type α. The diploids that
could not grow on glycerol could not sporulate.
What do the results of the mating say about the location of the cox2-1 mutation?
c. A different mutant strain of yeast called pet111-1
is also unable to grow on glycerol medium but still
can grow on glucose medium. These mutant cells
similarly lacked the cytochrome c oxidase. When
pet111-1 was crossed with a wild-type haploid
strain of the opposite mating type, the resultant
diploids were able to grow on glycerol and yielded
asci that all showed a 2:2 segregation of haploid
cells that could or could not grow on glycerol.
Explain these results in light of your answer to
part (b).
It is given that a mutant strain of Saccharomyces cerevisiae called cox2-1 lack a mitochondrial protein and cytochrome c oxidase. Also it is unable to grow a media having glycerol.
a) The cox2-1 cells are lacking mitochondrial proteins and thus their mitochondrial function is poor. In order to extract energy from sources like non fermentable substrates such as glycerol the organism need functional mitochondria as well as oxygen. Since the cox 2-1 is lacking mitochondria they are unable to use glycerol as a sole source of energy and carbon. Thus they are using glucose as source of carbon and grows on fermentable media containing glucose.
b) The cross between cox 2-1 mutant cells and wild type strain will result in the formation of diploid yeast cells which contain mitochondria inherited from both the parents. About half of the diploid yeast cells could develop a non-fermentable substrate and these cells resulted in a 4:0 segregation of phenotype upon meiotic division. This indicates that cox2-1 gene is a mitochondrial gene.
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