glycogen synthesis via UDP Glucose

Question 1

Why must G1P be converted to UDP-glucose first before it can be added to glycogen?

Answer 1

Adding G1P to glycogen has a positive delta G at ALL physiological concentrations of Pi.
Converting to UDP glucose is a way to “beat the system”

Question 2

UDP-glucose

Answer 2

high energy compound,
uridine base, set of phosphates anhydrides and esters to attach to sugar.
Common trend for polymerization to utilize these types of sugars .

Question 3

If pyrophosphate (PPi) is lost, why do we call the product UDP-Glucose?

Answer 3

Still had a phosphate, and still attached to phosphate, so still a di phosphate.

Question 4

is G1P attacking UDP a NAS or SN2 reaction?

Answer 4

SN2, because the Pi on G1P is attacking the Phosphate of UTP

Question 5

reaction coupling

Answer 5

occurs with inorganic pyrophosphatase (PPi-ase).
Ubiquitous enzyme, doing many rxn coupling in many different cells .
Provides the driving force for glycogen synthesis, which is hidden UTP-hydrolysis

Question 6

hUGPase is a small compound, but…

Answer 6

hUGPase forms octomeric complex, so can build big systems