Glycogenesis (glycogen anabolism)

Question 1

T or F: Blood glucose will go through few transformations before being integrated in the chain

Answer 1

True: Formation of linear chains [(α1->4) bonds]
Formation of side chains [(α1->6) bonds]

Question 2

Glycogenesis occurs in

Answer 2

Liver and muscle

Question 3

Glycogenesis reaction 1

Answer 3

Glucose is phosphorylated to form Glucose-6-phosphate (G6P) by the hexokinase and requires an investment of ATP

Question 4

Glycogenesis reaction 1 is catalyzed by

Answer 4

hexokinase I, II and III (muscle)

or

hexokinase IV/glucokinase (liver)

Question 5

Glycogenesis reaction 1 is catalyzed by

Answer 5

hexokinase I, II and III (muscle)

or

hexokinase IV/glucokinase (liver)

Question 6

Glycogenesis reaction 2

Answer 6

Glucose-6-phosphate is isomerized to Glucose-1-phosphate (G1P) by the phosphoglucomutase
-Reversible

Question 7

Reaction 3 Glycogenesis

Answer 7

Glucose-1-phosphate is activated in UDP-Glucose by the UDP-glucose pyrophosphorylase and is driven by the hydrolysis of the pyrophosphate from the uridine triphosphate (UTP)

Question 8

T or F: UDP-glucose is an activated intermediate that will be used as building blocks in the growing glycogen chain

Answer 8

True

Question 9

UDP-glucose is a

Answer 9

High energy compound so converse of UDP-glucose to glycogen has lots of free energy because of 2 ATP investment

Question 9

UDP-glucose is a

Answer 9

High energy compound so converse of UDP-glucose to glycogen has lots of free energy because of 2 ATP investment

Question 10

Glycogenesis Reaction 4

Answer 10

Synthesis of linear chains (α1->4): Glucose from UDP-glucose is transferred to the nonreducing end of a glycogen primer or a linear chain undergoing elongation

Question 11

Glycogen Primer

Answer 11

Short chain of glucose residues linked to a small protein named glycogenin (37 kDa).

Question 12

Reaction 4 glycogenesis is catalyzed by

Answer 12

glycogen synthase

Question 13

T or F: UDP-glucose is a high-energy compound, the glycogen synthase reaction is endergonic

Answer 13

False, exergonic

Question 14

Reaction 5 glycogenesis

Answer 14

Building side chains (α1->6) bonds: After linear chain formation of about 11 molecules of glucose, the last 6 or 7 glucoses of the non-reducing ends are detached and transferred onto a glucose closer to the reducing end, where the formation of an O-glycosidic (α1->6) bond ties the 6 glucose side branch to the linear branch.
**This reaction is performed by the branching enzyme, amylo-(1,4->1,6)-transglycosylase and is repeated over and over again to form glycogen

**Image: So what happens is you take the first 6 glucose, then move the last 4 up as shown in the second row

Question 15

Glycogenesis Reaction 6

Answer 15

Extension of the new glycogen molecule by elongation of the branches and formation of new (α1->4) bonds by glycogen synthase and addition of new side branches (new (α1->6) bonds by branching enzyme).

Question 16

Glycogenesis ATP requirment

Answer 16

Each glucose added onto glycogen costs 2 ATP:

1. Conversion of glucose into G6P (1 ATP)
2. UTP is then use to transform G1P in UDP-glucose. The end product is UDP. One ATP equivalent is needed to convert UDP into UTP (1 ATP)