Which of the following statement about mass spectroscopy is incorrect? a. MS ion

Question

Which of the following statement about mass spectroscopy is incorrect? a. MS ionizes the sample and then measures the time it takes for the ions to reach the detector. b. SELDI-MS has great potential for analyzing protein profiles of body fluids and may, in the future, be used to identify diseases before symptoms appear. c. Glycosylation and phosphorylation of proteins can be identified using ESI or MALDI. d. ESI is able to handle much larger ions than MALDI. e. The time-of-flight for ions is directly correlated with the mass of the ion in mass spectroscopy. Which of the following statements is not true about sequencing peptides with mass spectroscopy? a. The entire protein can be sequenced all at once using mass spectroscopy. b. Some purified proteins must be digested with proteases to eliminate undesirable characteristics such as hydrophobicity and solubility. c. Two rounds of mass spectroscopy are used to determine the sequence. d. In order to determine the sequence, a pure sample of protein is obtained through 2D-PAGE or HPLC. e. A database of protein ion spectra is used to compare the peaks of the unknown peptide to determine the sequence. Which of the following is used to quantify proteins with mass spectroscopy? a. 2H n b. 33P c. 35S d. 32P e. 125| Why are protein tags useful? a. Protein tags are exactly the same thing as reporter fusions and perform similar functions. b. Tags allow the protein to be isolated and purified from other cellular proteins. c. Tags allow the protein to be quantitated. d. Protein tags enable the protein to which they are fused to perform their function more readily. e. None of the above.

Explanation / Answer

6. d) as MALDI is used for larger ions but not the ESI. MALDI(Matrix Assisted LASER Desorption Ionisation) is a soft ionisation method in which fragmentation is less enabling to identify macromolecular ion. whereas ESI(electron spray ionisation) is comparatively harder ionisation method where there is high chance of fragmentation. It is generally not used for identifying big molecules.

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