4 glucose metabolism 2 Flashcards
In humans, what is the blood glucose level maintained at?
**80-100mg/dl **
even though carbohydrate intake varies in a day
what is excess glucose converted to in vertebrates?
glycogen for storage
Where can glycogen be found? In what form?
primarily in liver and skeletal muscle in large cytosolic granules
How much weight does glycogen represent in the liver and muscles?
10% of weight in liver
1-2% of weight of muscles
liver is closer to factory = easy to transport
when do strenous exercise, liver is too far, so use glucose in muscle
What is glycogen in muscles for?
quick source of energy for either aerobic or anaerobic metabolism, especially during exercise
How long until muscle glyogen is depleted during vigorous exercise?
can be depleted inless than 1 hour
what is liver glycogen used for?
a reservoir of glucose for other other tissues when dietary glucose is not available (between meals or during fasting)
How long until liver glycogen storage is depleted?
12 to 24 hours
which glucose units of glycogen are cleaved in liver and skeletal muscles?
the glucose units of the outer branches
Where do the glucose units cleaved form the outer branches of glycogen go?
enter the glycolytic pathway via the action of 3 enzymes
* Glycogen phosphorylase
* glycogen debranching enzyme
* phosphoglucomutase
What does the enzyme glycogen phosphorylase do in glycogen breakdown?
removes the terminal glucose residues from the nonreducing end until it reaches a point of 4 glucose residues away from the (α1 to 6) branch point
as it snips will add one phosphate group
produces glucose 1 phosphate (G1P) = cannot enter glycolysis
What is the product of glycogen phosphorylase?
G1P
Can G1P enter glycolysis?
no
What is the difference between G1P and G6P?
G6P = phosphate is at 6 carbon
G1P = phosphate at 1 carbon
what cant recognise G1P?
second enzyme can recognize G1P to convert it into fructose 6 phosphate
What does the glycogen debranching enzyme do in glycogen breakdown?
transfers the branches (yellow), leaving a single glucose residue at the branch point (red)
this single glucose residue is then released and can enter directly into glycolysis
glycogen phosphorylase rxn will resume on a new unbranched polymer
What is G1P, end product of glycogen phosphorylase converted to?
G6P by phosphoglycomutase
moves phosphate from C1 to C6
now G6P can enter glycolysis, PPP or replenish blood glucose
Where can glycogen synthesis take place in animals?
in almost all animal tissues
especially prominent in liver and skeletal muscles
What is the starting point of glycogen synthesis?
G6P
G6P is converted to G1P and then to UDP-glucose
G6P can be reverted back into G1P using phosphoglucomutase again
UDP-glucose is a nucleotide called UDP carrying G1P to extend glycogen branch
What is UDP-glucose?
the immediate donor of glucose residues for glycogen synthesis
UDP-glucose is a nucleotide called UDP carrying G1P to extend glycogen branch
What is the glycogen chain elongated by?
glycogen synthase
the glucose residue of UDP-glucose is transferred to the nonreducing end of a glycogen branch to make a new (α1 to 4) linkage
α1-4 is linear chain
glycosidic bond
How are α1-6 bonds at branch points of glycogen?
glycogen-branching enzymes used
* a chian of 6-7 sugars is removed from a branch of at least 11 sugars long and each new branch point must be at least 4 sugars away form the nearest exisiting branch point
What enzyme is used to make α1-4 and α1-6 linkage in glycogen synthesis
α1-4 - glycogen synthase
α1-6 - glycogen branching enzyme
