2 - Protein to Proteome PDF

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Protein to Proteome...

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N-linked oligosaccharides on secreted glycoproteins are attached to ________. (a) nitrogen atoms in the polypeptide backbone. (b) the serine or threonine in the sequence Asn-X-Ser/Thr. (c) the N-terminus of the protein. (d) the asparagine in the sequence Asn-X-Ser/Thr. D (the asparagine in the sequence Asn-X-Ser/Thr) Which of the following statements about disulfide bond formation is false? (a) Disulfide bonds do not form under reducing environments. (b) Disulfide bonding occurs by the oxidation of pairs of cysteine side chains on the protein. (c) Disulfide bonding stabilizes the structure of proteins. (d) Disulfide bonds form spontaneously within the ER because the lumen of the ER is oxidizing. D (disulfide bonds form spontaneously within the ER because the lumen of the ER is oxidizing) Cells have oligosaccharides displayed on their cell surface that are important for cellcell recognition. Your friend discovered a transmembrane glycoprotein, GP1, on a pathogenic yeast cell that is recognized by human immune cells. He decides to purify large amounts of GP1 by expressing it in bacteria. To his purified protein he then adds a branched 14-sugar oligosaccharide to the asparagine of the only Asn-XSer sequence found on GP1 (Figure Q15-48). Unfortunately, immune cells do not seem to recognize this synthesized glycoprotein. Which of the following statements is a likely explanation for this problem? Figure Q15-48 (a) The oligosaccharide should have been added to the serine instead of the asparagine. (b) The oligosaccharide should have been added one sugar at a time. (c) The oligosaccharide needs to be further modified before it is mature. (d) The oligosaccharide needs a disulfide bond. C (the oligosaccharide need to be further modified before it is mature) Different glycoproteins can have a diverse array of oligosaccharides. Which of the statements below about this diversity is true? (a) Extensive modification of oligosaccharides occurs in the extracellular space. (b) Different oligosaccharides are covalently linked to proteins in the ER and the Golgi.

(c) A diversity of oligosaccharyl transferases recognizes specific protein sequences, resulting in the linkage of a variety of oligosaccharides to proteins. (d) Oligosaccharide diversity comes from modifications that occur in the ER and the Golgi of the 14-sugar oligosaccharide added to the protein in the ER. D (oligosaccharide diversity comes from modifications that occur in the ER and the Golgi of the 14-sugar oligosaccharide added to the protein in the ER)...