Chapter 24 & 25 Flashcards
glycogen
highly branched homopolymers of glucose present in all tissues
largest stores of glycogen are in…
the liver and muscle
Liver breaks down glucose and releases it to..
blood to provide energy for brain and RBC
muscle glycogen stores are mobilized to provide energy for…
muscle contraction
glycogen is synthesized and degraded by…
different pathways
glycogenolysis
degradation of glycogen
glycogenesis
biosynthesis of glycogen
UDP-GLucose
an activated form of glucose
phosphoglucomutase
reversible rex between glucose 6-P and glucose 1-P
glucose 1-P is converted to UDP-glucose by..
UDP glucose pyrophosphorylase
glycogen synthase
transfers a glucose moiety from UDP-glucose to C-4 terminal of glycogen to form an a-1,4-glycosidic bond
Why is branching important?
increases rate of glycogen synthesis and degradation by increasing solubility of glycogen, creating a large number of terminal residues
terminal residues
sites of action of glycogen phosphorylase and synthase
a-1,4 linkage to a-1,6 linkage
- UDP-glucose + glycogen synthase
- branching enzyme
initiation of glycogenesis
- self catalyzed attachment of glucose residue to Tyr 194 OH group of glycogenin
- extension of the gluten chain up to 8 glucose residues, forming the primer for initiation of glycogen synthesis
- glycogen synthase further extends chain
glycogen phosphorylase
degrades glycogen from nonreducing ends of glycogen molecule; yields glucose 1-P
glucose 1-P is converted to glucose 6-P by…
phosphoglucomutase
glycogen phosphorylase can only cleave..
near branch points and only at a-1,4-glycosidic bonds
How does glycogen phosphorylase degrade the remainder of the glycogen molecule?
transferase and a-1,6-glucosidase react to form a linear chain with all a-1,4 linkages suitable for further cleavage by phosphorylase
glucose 6-phosphatase is present in…
liver and absent in most other tissues
glucose 6-phosphatase generates…
free glucose from glucose 6-phosphate in liver
difference between active and inactive glycogen phosphorylase
active has a phosphate group
phosphorylase phosphatase
converts active GP to inactive GP by removing phosphate group from serine residue (release if Pi)
phosphorylase kinase
converts inactive GP to active by adding a phosphate group to serine residue (IN PRESENCE OF ATP)
In muscle, what inhibits GP
ATP and G6-P
in muscle, what activates GP?
AMP
in the liver, what inhibits GP?
glucose
difference between active and inactive glycogen synthase?
inactive form has a phosphate group
protein kinases (GSK-3)
inactivates active form of GS with addition of phosphate group in presence of ATP
protein phosphatases (PP1)
activates inactive form of GS by removing phosphate group and releasing Pi
in both muscle and liver, what activates GP “b”?
glucose 6-P
glucagon is produced in..
in pancrease
epinephrine is produced in ..
adrenal glands
2 WAYS INSULIN ACTIVATES GLYCOGEN SYNTHESIS?
- INACTIVATES GSK-3
- ACTIVATES PP1
