3.) Bacteria have many traits that are of economic interest. A new strain of the

Question

3.) Bacteria have many traits that are of economic interest. A new strain of the bacterial species Shinorhizobium meliloti leadii (one of many symbiotic bacteria that fix nitrogen in the roots of legumes) has been found to produce and exude a polysaccharide compound that binds to toxic lead. This compound, if it can be produced economically, could be useful for decontaminating soil that contains lead and other toxic metals.

A) Design an experiment that would prove which macromolecule (DNA, RNA, or Protein) carries the information for making this lead-binding polysaccharide.

B)If you knew that 3 different proteins are required to make this polysaccharide, each only found in the new strain, Streptococcus meliloti leadii, how would you need to adjust your experiment?

Explanation / Answer

A)

Since, Shinorhizobium meliloti leadii is a bacterium, it must be containing the plasmid DNA (Extra circular DNA) carrying genes encoding the polysaccharide that binds to lead. Therefore, transformation experiment can be carried out to prove the DNA contains the information for making lead binding polysaccharide. First, this gene must be identified by DNA sequencing. Then the gene is cut with a restriction endonuclease and inserted into a plasmid. An antibiotic resistance gene is also inserted.

The sinorhizobium cells that do not exude the polysaccharide (Sin-) are mixed with cells that produce the polysaccharide(Sin+) . Through transformation the Sin- cells acquire the gene encoding polysaccharide and Sin- cells become Sin+ cells. The transformed cells can be screened by growing in a medium containing antibiotic resistance gene, since the plasmid contains the antibiotic resistance gene, the cells do not grow in this medium. By this screening it can be known that the Sin- cells have become Sin+ cells by acquiring the gene encoding polysaccharide that binds to lead.

B)

If three different proteins are required to make the polysaccharide, then the 3 genes encoding the proteins are isolated and cut with restriction endonuclease and inserted into plasmid.Thus, three genes also inserted in to plasmid DNA get transformed into Sin- cells.

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