Exam 2 Lecture 17 Glycogen Metabolism I Flashcards
the structure of glycogen is a long chain _ of glucose with branches
homopolymer
glucose molecules within linear chain linked together via _
alpha-1,4 glycosidic bonds
branched points formed via _ bonds between glucose monomers of separate chains
alpha-1,6 glycosidic bonds
_ contain a terminal glucose with a free hydroxyl group at carbon 4
non-reducing ends (multiple)
_ consists of glucose monomer connected to a protein called glycogenin
reducing ends
glycogen is _ and _ from non-reducing ends
degraded and extended
glycogen is stored in:
liver, muscle, and other tissue
glycogen is stored as _
granules
granules contain not only glycogen but also the _ needed for glycogen metabolism
enzymes needed for glycogen metabolism
defects in glycogen enzymes can lead to disorders termed _
glycogen storage disorders
liver glycogen regulates
blood glucose levels (sensor)
muscle glycogen provides
reservoir of fuel (glucose) or physical activity
T/F: glycogen metabolism is regulated storage and release of glucose
true
T/F: glycogen metabolism synthesis and degradation of glycogen involve the same pathways
false; synthesis and degradation are INDEPENDENT of each other
Pathways in glycogen metabolism are regulated independently?
yes
how does muscle glycogen supply energy
breaks down glycogen and keeps glucose in the muscle to use for activity
what are the ways to regulate glycogen metabolism?
- allosteric control
- covalent modification
- hormonal control
how does allosteric control regulate glycogen metabolism
want to control enzyme to influence the activity of the enzyme (induces conformation change)
how does covalent modification regulate glycogen metabolism
mainly through phosphorylation; reversible
how do hormones regulate glycogen metabolism
insulin stimulates phosphatase, glucagon stimulates a kinase (PKA) ie hormones control covalent modifications
What are the 3 key steps to glycogenesis
- trapping and activation of glucose
- elongation of a glycogen primer
- branching of glycogen chains
how does trapping of glucose occur?
glucokinase/hexokinase in cytosol of hepatocytes and muscle cells catalyze phosphorylation of glucose into glucose-6-ohosphate
hows does activation of glucose occur?
phosphoglucomutase then reversibly isomerizes glucose-6-phosphate into glucose-1-phosphate. UDP-glucose pyrophosphorylase then transfers glucose-1P tp UTP which generates UDP-glucose (active form of glucose)
UDP is for _
synthesis
how does elongation occur?
elongation via glycogen synthase (rate limiting enzyme). Have a existing glycogen primer and glycogen synthase catalyzes transfer of glucose from UDP-glucose to non-reducing end of glycogen chain
glycogen synthase forms _ glycosidic bonds between glucose molecules
alpha-1,4
how does branching of glycogen chains occur?
when a glycogen chain reaches about 11 residues, a fragment of the chain (about 7 residues long) is broken off at an alpha-1,4 link and reattached elsewhere
in branching, an alpha-1,4 link is broken off and attached through an _ link
alpha-1,6 link
what enzyme is used for branching?
glucosyl (4:6) transferase
Branching increases _
solubility of glycogen and increases # of terminal non-reducing ends
glycogen degradation aka
glycogenolysis
glycogen broken down to release _
glucose-1-phosphate (rate limiting step)
_ remodeled to permit further degradation
glycogen remnant
in glycogenolysis, glucose-1-phosphate converted to
glucose-6-phosphate
glucose-6-phosphate from glycogenolysis can now enter various pathways which are:
- glycolysis
- free glucose for release into blood stream
- pentose phosphate pathway-NADPH and ribose derivative (nucleic acid synthesis)
how many key enzymes for glycogenolysis?
4
what is the rate limiting enzyme in chain shortening
glycogen phosphorylase (GP) catalyzes the cleavage of glycogen
chain shortening occurs at the _ end of the polymer
non-reducing end
GP adds an _ and releases a glucose residue as glucose-1-phosphate
orthophosphate
GP uses _ as a cofactor
pyridoxal phosphate (Vit B6)
phosphorolysis of glucose residues continues until the GP gets within _
4 residues of the alpha-1,6 linkage of a branch point
what does the phosphoglucomutase step do and how does it work?
mutase removes phosphate from the 1 position to the 6 position ie converts glucose-1P to glucose-6P. Adds the phosphate to position 6 first then removes phosphate from position 1
in branch transfer, the enzyme _ transfers a block of 3 of the remaining 4 glucose to the non-reducing end of the main chain forming an alpha-1,4 bond
transferase
the debranching enzyme _ cleaves the alpha-1,6 bond of the single remaining glucose residue to release the free glucose
alpha-1,6 glucosidase
in release of glucose, glucose is phosphorylated by _
hexokinase
together, transferase and alpha-1,6 glucosidase convert _ glycogen into a _ structure for further action by GP
convert branched glycogen into a linear structure
in debranching, _ cuts at non-reducing end
phosphorylase
in debranching of glycogen, yields _ G1P to 1G
10 G1P to 1G
T/F: glucose-6P cannot get out of the cell
true
only _ has glucose-6-phosphatase (present in the ER)
liver
muscle cells do not have glucose-6-phosphatase so _ stays
glucose-6P
small amount of glycogenolysis via _
lysosomal alpha-1,6 glucosidase (acid maltase)
