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Glycogenin is a homodimer of 37 kDa subunits. (Homodimer means identical subunits of type a that form a dimer of type a₂). Glycogenin has a chain of a(1,4)-linked units of glucose attached to the sidechain of a tyrosine residue. The chain of a(1,4)-linked glucose units is a primer for the initiation of glycogen synthesis by glycogen synthase. Assume the dimer is stable and not in equilibrium with monomer subunits. Which of the answers below are plausible pathways for attaching or building the primer chain of glucose units? The branching enzyme attaches a chain of 7 glucose units to the tyrosine sidechain of glycogenin. The transferase attaches 3 units of a(1,4)-linked glucose to the tyrosine sidechain of glycogenin. Glycogen synthase then extends the chain using UDP-GIC. One glycogenin dimer builds the a(1,4)-Ilinked glucose chain on a subunit of another glycogenin dimer. Each subunit builds the a(1,4)-llinked glucose chain on the other subunit of the same dimer.

Glycogenin is a homodimer of 37 kDa subunits. (Homodimer means identical subunits of type a that form a dimer of type a₂). Glycogenin has a chain of a(1,4)-linked units of glucose attached to the sidechain of a tyrosine residue. The chain of a(1,4)-linked glucose units is a primer for the initiation of glycogen synthesis by glycogen synthase. Assume the dimer is stable and not in equilibrium with monomer subunits. Which of the answers below are plausible pathways for attaching or building the primer chain of glucose units? The branching enzyme attaches a chain of 7 glucose units to the tyrosine sidechain of glycogenin. The transferase attaches 3 units of a(1,4)-linked glucose to the tyrosine sidechain of glycogenin. Glycogen synthase then extends the chain using UDP-GIC. One glycogenin dimer builds the a(1,4)-Ilinked glucose chain on a subunit of another glycogenin dimer. Each subunit builds the a(1,4)-llinked glucose chain on the other subunit of the same dimer.

Biochemistry
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
Section: Chapter Questions
Problem 1P
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1 2 Glycogenin is a homodimer of 37 kDa subunits. (Homodimer means identical subunits of type a that form a dimer of type a2). Glycogenin has a chain of a(1,4)-linked units of glucose attached to the sidechain of a tyrosine residue. The chain of a(1,4)-linked glucose units is a primer for the initiation of glycogen synthesis by glycogen synthase. Assume the dimer is stable and not in equilibrium with monomer subunits. Which of the answers below are plausible pathways for attaching or building the primer chain of glucose units? The branching enzyme attaches a chain of 7 glucose units to the tyrosine sidechain of glycogenin. 0 0 0 0 000 The transferase attaches 3 units of a(1,4)-linked glucose to the tyrosine sidechain of glycogenin. Glycogen synthase then extends the chain using UDP-Glc. 0 One glycogenin dimer builds the a(1,4)-llinked glucose chain on a subunit of another glycogenin dimer. -D-O Each subunit builds the a(1,4)-Ilinked glucose chain on the other subunit of the same dimer. You suspect UDP-Glc modifies a sidechain of glycogenin other than the tyrosine of interest. What experiment would you perform to confirm your suspicions? Measure the rate of synthesis at a fixed concentration of glycogenin and multiple concentrations of UDP-Glc. Measure the rate of synthesis at fixed concentration of UDP-Glc and multiple concentrations of glycogenin. Make a mutant dimer, tyrosine to phenylalanine. Incubate the mutant dimer with UDP-Glc. Observe by mass spectroscopy whether there is an increase in mass consistent with a glucosyl unit. Do you have evidence to support you suspicion or do you just hear voices? If you have evidence then mutate the residue you think is modified and see what happens. -D=0
Transcribed Image Text:1 2 Glycogenin is a homodimer of 37 kDa subunits. (Homodimer means identical subunits of type a that form a dimer of type a2). Glycogenin has a chain of a(1,4)-linked units of glucose attached to the sidechain of a tyrosine residue. The chain of a(1,4)-linked glucose units is a primer for the initiation of glycogen synthesis by glycogen synthase. Assume the dimer is stable and not in equilibrium with monomer subunits. Which of the answers below are plausible pathways for attaching or building the primer chain of glucose units? The branching enzyme attaches a chain of 7 glucose units to the tyrosine sidechain of glycogenin. 0 0 0 0 000 The transferase attaches 3 units of a(1,4)-linked glucose to the tyrosine sidechain of glycogenin. Glycogen synthase then extends the chain using UDP-Glc. 0 One glycogenin dimer builds the a(1,4)-llinked glucose chain on a subunit of another glycogenin dimer. -D-O Each subunit builds the a(1,4)-Ilinked glucose chain on the other subunit of the same dimer. You suspect UDP-Glc modifies a sidechain of glycogenin other than the tyrosine of interest. What experiment would you perform to confirm your suspicions? Measure the rate of synthesis at a fixed concentration of glycogenin and multiple concentrations of UDP-Glc. Measure the rate of synthesis at fixed concentration of UDP-Glc and multiple concentrations of glycogenin. Make a mutant dimer, tyrosine to phenylalanine. Incubate the mutant dimer with UDP-Glc. Observe by mass spectroscopy whether there is an increase in mass consistent with a glucosyl unit. Do you have evidence to support you suspicion or do you just hear voices? If you have evidence then mutate the residue you think is modified and see what happens. -D=0
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