Identify the research question addressed as a whole and the experimental approac
ID: 142100 • Letter: I
Question
Identify the research question addressed as a whole and the experimental approaches used.
Describe each figure including how previous knowledge led to the question that prompted each experiment, how the question was addressed through experiments, and the results and conclusions of each experiment.
Explain each experiment and identify the controls.
Discuss other approaches to answer the same question.
Evaluate the validity of the author’s conclusions.
A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus
Felisa Wolfe-Simon, et al. Science 332, 1163 (2011); http://science.sciencemag.org/content/332/6034/1163
Explanation / Answer
This paper tells us about the bacteria isolated from Mono lake in California which is of strain GFAJ-1. This strain can substitute aresenic (As) for the element phosphorus (P) to sustain it's growth. The data in the experiment indicates that GFAJ-1 can survive and grow in the presence of high aresnate concentration and thereby incorporate some arsenic ninto cellular constituents, their evidence for arsenate dependent growth is weak.
Experimental approaches used Wolfe Simon et Al measured the percentage of aresenic and phosphrous in dry weight of the bulk intracellular material of the samples. To summarize the difference between the samples, Wolfe Simon et Al reported ratio of As:P for each individual sample measurement and then average of both ratio which were incorrect.Data had poor quality in terms of correction coefficients. Wolfe Simon et Al used high resolution secondary ion mass spectrometer to identify Aresenic in extracted ,gel purified DNA. This data presented by Wolfe Simon et Al do not show the Aresenic is biochemically Incorporated into DNA of strain GFAJ-1. More additional chemical and structural analysis showing the replacement of phosphrous by aresnate should have been provided.
Questions addressed was " could a microbe or bacteria with strain GFAJ-1 use aresenic in place of phosphrous to sustain it's growth. Results included inductively coupled mass spectrometer , results revealed aresenic was inside bacterial cells suggesting it was not only a contaniment stuck yo the exterior of cells. Wolfe Simon et Al allowed to spot the normal toxic substance within the protein,lipid,nuc nucleic acid and metabolite fraction of cells through radioactive labeling of arsenic. This suggested molecules forming each fraction. Reports of evidence suggested the isolated DNA still contained Arsenic.Results of high intensity X-rays analysis gave Wolfe Simon et Al evidence that arsenic bin bacteria did appear to be replacing phosphorus in DNA and other molecules. This was the conclusion they came up.Primary conclusion of Wolfe Simon et Al said that the bacterium that can grow in presence of high aresnate is incorrect. This research article accompanied new articles to conveyed the extent to which hypothesis says that aresenic replaces phosphorus in biomolecules such as DNA must manage well rates for the hydrolysis of aresenic esters and the phosphate DNA might "morph" into aresenic DNA upon going from a phosphrous rich environment to a phosphrous poor environment creates a interesting paradox with respect to metabolism.
Validity of conclusion is this paper needs a rewritting as arseno DNA exists, then much of the past century of work will arsenate and phosphrous chemistry and metabolic pathways.