It consists of 5-carbon deoxyribose sugars and phosphate groups. These sugars are linked together by a phosphodiester bond , between carbon 4 of their chain, and a CH 2 group that is attached to a phosphate ion. They are extremely important in the function of DNA. Figure 1 Diagram showing the sugar phosphate backbone of DNA, and the nitrogenous bases attached to it, forming a nucleotide [1].
DNA is wound into an right-handed double helix. Control cultures supplemented with all three nutrients in the form of glucose, ammonium chloride and potassium phosphate were compared to cultures in which each one of the substances, respectively, was omitted. In each case three independent cultures were grown, and average growth curves and their standard deviations are shown in Fig.
In the absence of externally added genomic DNA no growth occurred when C was omitted, indicating that Hfx. In contrast, considerable growth occurred when P was omitted, showing that Hfx. However, in preparation of future genetic experiments Hfx.
Therefore, uracil had to be supplemented, which might have been used as nitrogen source, and thus the experiment is uninformative about the absence or presence of an internal nitrogen storage pool. In additional cultures each one of the three nutrients was replaced with genomic DNA dotted lines , i. C was replaced squares , N was replaced circles , and P was replaced triangles. In further cultures each one of the respective nutrients was omitted without replacement solid lines , i.
C was omitted squares , N was omitted circle , and P was omitted triangles. To verify that spill over did not occur, for each medium also non-inoculated controls sterile controls were performed open symbols. In each case average values of three independent cultures and their standard deviations are shown. The addition of external genomic DNA to cultures lacking any of the three nutrients in all three cases enhanced the growth yield, revealing that genomic DNA can be a source for C, N, and P for Hfx.
The addition of genomic DNA to cultures lacking phosphate or ammonium resulted even in faster growth compared to the control culture grown in the presence of all three nutrients. Only the culture with genomic DNA instead of glucose as a C-source had a substantially lower growth rate, showing that genomic DNA is metabolized more slowly than glucose as a carbon source.
These results revealed on the one hand that external environmental DNA can be used as a source for C, N, and P, and on the other hand showed that Hfx. In the following experiments we concentrated on the usage of external genomic DNA as a source of P and the identity of the intracellular P storage polymer.
To further confirm that high molecular weight genomic DNA was indeed the source of the phosphorous, and not potential impurities or contaminations, Hfx. As a control, non-inoculated cultures were incubated under identical conditions. Notably, the OD values of Fig. At the eight time points indicated in Fig.
The DNA content of the supernatant was analyzed by analytical agarose gel electrophoresis after dialysis to remove the high salt concentration of the medium. It can be seen that the high molecular weight input genomic DNA is broken into small fragments, either by chemical hydrolysis or, more probable, by mechanical shearing forces due to the shaking with rpm. Taken together, these results clearly show that Hfx. Three Hfx. As negative controls three non-inoculated cultures were incubated under identical conditions solid line, circles.
At the indicated times the optical densities were recorded and aliquots were removed for the quantification of the DNA content. Average optical densities and their standard deviations are shown solid lines. The cells were pelleted by centrifugation and the DNA content of the supernatants was analyzed by analytical agarose gel electrophoresis compare B and C. The DNA concentration was quantified using ImageJ, and average values and their standard deviations are shown dotted lines, circles for the mock-treated non-inoculated control, squares for the inoculated culture.
The supernatants of the aliquots of non-inoculated negative control cultures were dialyzed to remove salts and analyzed by analytical agarose gel electrophoresis. One representative gel is shown. The supernatants of the aliquots of cultures grown with genomic DNA as phosphate source were dialyzed to remove salts and analyzed by analytical agarose gel electrophoresis.
For a further characterization of the growth of Hfx. The results are shown in Fig. Growth with 1 mM and with 10 mM phosphate was identical, indicating that phosphate is not the limiting nutrient under these conditions. Again, considerable growth was observed in the absence of added P, indicating that the liberation of phosphate from the intracellular phosphate storage polymer is growth rate-limiting.
The OD at the start of the experiment was about 0. The sterile controls showed that the microtiter plates had and OD of about 0. After h growth in the absence of added P the cells had an OD of about 0. This is an 8. Microscopic observation of the cells indicated that they had normal morphology and were of similar size.
Non-inoculated sterile controls were also incubated dotted lines. Growth was followed by measuring the optical density at nm. Average values of three independent cultures and their standard deviations are shown.
These observations that Hfx. To test our hypothesis we used Hfx. Using quantitative PCR qPCR , chromosome copy numbers were estimated for the inoculum an estimate of the pre-growth condition as well as cells grown to exponential phase and stationary phase without added phosphate exponential phase: 9.
During exponential growth, the phosphate concentration was found to influence the ploidy level, with 24 copies on average in cells grown with 10 mM phosphate, 19 copies in cells grown with 1 mM phosphate, and 14 in cells grown in the absence of an added source of phosphorous Fig.
Stationary phase cells that were grown in the presence of added phosphate 10 and 1 mM maintained approximately 13 chromosomal copies of their genome. However, in the absence of phosphate supplementation, stationary cells had on average reduced their genome copy number to two. This result showed that Hfx. DNA repair, desiccation resistance, long term survival to enable short-term reproductive gains. Aliquots were removed during mid-exponential growth phase and at stationary phase compare text.
An aliquot from the pre-culture used for inoculation was also included. Cells were harvested by centrifugation and the chromosome copy number was quantified using Real Time PCR.
Three biological replicates were performed and average values and standard deviations are shown, from left to right 10 mM phosphate, 1 mM phosphate, and no externally added phosphate.
Polyploidy dependence upon nutrient availability was further substantiated when cells from P-starved stationary phase cultures that were depleted of extra chromosomes were amended with phosphate: within three hours the chromosome copy number more than tripled and within 24 hours they increased by greater than fold to more than 40 copies per cell Fig.
Thus phosphate-starved Hfx. Stationary phase, phosphate-starved, chromosome-depleted cells were resuspended in medium containing 1 mM phosphate. At various times, as indicated, aliquots were removed and the chromosome copy number was determined using Real Time PCR. Three biological replicates were performed and average values and standard deviations are shown. The genome sequence of Hfx. To investigate this possibility, Hfx. The cells were fixed and stained with DAPI to simultaneously detect genomic DNA as well as polyphosphate based on the differential wavelengths of fluorescence emission for these biopolymers [18].
Chromosomal DNA was readily observed in cells using this approach, in contrast to polyphosphate, which was not detected data not shown.
Therefore, at least under the conditions of the experiments of this study, Hfx. However, it should be noted that even the detection of polyphosphate would not have disproven our observation that Hfx. The results showed that during growth under phosphate starvation Hfx. Another possible source of phosphate might be ribosomal RNA. The numbers of ribosomes per cell are influenced by parameters like growth rate and it can vary widely, both in E. Therefore, for a better understanding of the phosphate balance of cells during phosphate starvation, also the number of ribosomes was quantified.
The cell density was quantified and increased from 3. The number of ribosomes prior to and after phosphate starvation was quantified using a previously described approach [20]. Together these results revealed that ribosomal RNA is neither source nor sink of phosphate during phosphate starvation, but that ribosomes are distributed among the daughter cells and that the phosphate content bound in rRNA is self-sufficient during phosphate starvation.
Email address: Your name:. Possible Answers: Phosphodiester linkage. Correct answer: Phosphate backbone. Explanation : The phosphate backbone of DNA is negatively charged due to the bonds created between the phosphorous atoms and the oxygen atoms. Report an Error. Possible Answers: ADP. Correct answer: All answer choices. Explanation : Nitrogen is essential to create all the nucleic acids, and phosphorous is essential to create phospholipids an obvious choice , ATP and ADP they are the same class of molecule, and the P stands for phosphate , and DNA for the phosphate-sugar backbone.
Which of the following is not true of a DNA molecule? Possible Answers: A purine or pyrimidine is bound to each sugar-phosphate group. Adenine and thymine are held together by phosphodiester bonds. Complementary strands are held together by hydrogen bonds. Correct answer: Adenine and thymine are held together by phosphodiester bonds. Explanation : DNA is a polymer composed of nucleotide monomers. Possible Answers: ionic.
Correct answer: covalent. Explanation : The bond formed between the sugar of one nucleotide and the phosphate of an adjacent nucleotide is a covalent bond. Copyright Notice. DNA, or deoxyribonucleic acid, is the heritable material found in all cells. DNA provides the instructions to build, maintain, and regulate cells and organisms and is passed on when cells divide and when organisms reproduce. In this unit, the molecular structure of DNA and its packaging within cells will be examined.
A helix is a winding structure like a corkscrew; DNA is known as a double helix because there are two intertwined strands within each molecule of DNA. In the image above, a corkscrew is shown on the left, with the helical region labeled.
The image in the center shows the structure of DNA. Note that there are two strands: one shown in blue, one in yellow. Other examples of a helix include yarn, a phone cord, or a spiral staircase.
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