The reaction between UTP and glucose-1-phosphate (G1P) to form UDP-glucose in glycogenesis is shown below: Which phosphates from the reactants are present in UDP-glucose?

Question

The reaction between UTP and glucose-1-phosphate (G1P) to form UDP-glucose in glycogenesis is shown below:  Which phosphates from the reactants are present in UDP-glucose?

Quizplus · Accepted Answer

11ecba2d_0edf_69b1_a3bf_bbbe1035406a_MD0008_00 Anabolism is the synthesis of complex biological molecules from simpler constituents, and it requires energy input. The energy needed for anabolic processes is generally provided by cleaving high-energy phosphodiester bonds in nucleotide triphosphates (NTPs) such as ATP, GTP, or UTP. The three phosphate groups on an NTP are designated as the α-, β-, and γ-phosphates, with the α-phosphate being linked to the nucleoside and the γ-phosphate being farthest away from the nucleoside. NTP cleavage typically releases either the γ-phosphate as inorganic phosphate (P_i) or the γ- and β-phosphates as pyrophosphate. Glycogenesis is the anabolic synthesis of glycogen from glucose molecules. In the second-to-last step of glycogenesis, the C1 phosphate of G1P acts as a nucleophile to attack the α-phosphate of UTP. The bond between the α- and β-phosphates breaks, and the β- and γ-phosphates are released as pyrophosphate. Accordingly, the two phosphates that are incorporated into UDP-glucose are the α-phosphate from UTP and the C1 phosphate of G1P. (Choices A and B) Following the reaction shown, the α-phosphate from UTP is present in UDP-glucose, but the β- and γ-phosphates are released as pyrophosphate. (Choice C) The γ-phosphate is the furthest phosphate from uridine in UTP. It is part of the pyrophosphate leaving group, not UDP-glucose. Educational objective: Anabolic processes require energy input, which is typically provided by cleaving phosphodiester bonds in nucleotide triphosphates (NTPs) such as ATP, GTP, or UTP. These cleavage events either release the γ-phosphate as inorganic phosphate (P_i) or they release the γ- and β-phosphates as pyrophosphate. The α-phosphate remains attached to the NTP.

The Reaction Between UTP and Glucose-1-Phosphate (G1P) to Form UDP-Glucose