Glucose metabolism and gluconeogenesis Flashcards
At which end of glycogen is glc added/removed?
at the nonreducing end
Why store glucose as glycogen?
reduce osmotic pressure
Concentration gradient
Why glycogen instead of starch?
Glycogen has a high branching network which makes more glucose easier to access at one time when needed quickly.
Phospholysis of glycogen yields:
(glc)n-1 and glc-1-P by glycogen phosphorylase
G1P is then converted into G6P, which undergoes glycolysis in the muscle or is converted to glc and dumped into the blood in the liver
Can glc-1-P go directly into glycolysis?
Noap. Must first be converted to glc-6-P, ya ninny
By what process is the last glucose on a glycogen branch removed? what does it yield?
The final glucose is removed by hydrolysis, yielding glc (not G1P)
2 activities of debranching enzyme:
1) a(1–>4) transglycosylase (transferring the triglucoside)
2) a(1–>6) glucosidase (hydrolyzing off the glc)
input and output of ATP in glycolysis when starting with G6P (product of phosphorlyisis of glycogen)
1 ATP input in the beginning stages of glycolysis.
4 ATPs produced
Net: 3 ATPs yielded
5 basic steps of making glycogen
- convert glc to G6P (glucokinase)
- convert G6P to G1P (phosphoglucomutase)
- Further activate G1P by making UDP-glc
- Add a glc unit to the nonreducing end of a glycogen chain
- make branches
2 forms of phosphorylase
phosphorylas a (phosphorylated, more active form) phosphorylase b (not phosphorylated, less active)
What enzymes add/remove phosphate from phosphorylase a and b?
- can be attatched or removed by phosphorylase kinase
- removed by phosphorylase phosphotase
Hormone cascade which leads to the activation of Glycogen phosphorylase
(Phosphorylation system)
- [glc] low in blood = hormone GLUCAGON dumped in blood.
- glucagon binds to liver receptor, activating ADENYLATE KINASE which activates cAMP
- cAMP activates PKA
- PKA phospphorylates PHOSPHORYLASE KINASE, activating it.
- phosphorylase kinase phosphorylates phosphorylase, activating it
- phosphorylase phospholyses glycogen into G1P which becomes glc and is dumped in blood
signal amplification
a small amount of hormone (glucagon) will cause the activation of a large amount of phosphorylase.
Does muscle respond to glucagon?
No. That is a huger signal, therefore not the muscle’s problem
In the muscle, does AMP or ATP activate or inhibit phosphorylase?
AMP will activate phosphorylase
ATP inhibits it
Does phosphorylation of glycogen synthase turn it on or off?
turns it off
2 forms of glycogen synthase
1) glycogen synthase a (not phosphorylated, active)
2) glycogen synthase b (phosphorylated, inactive)
(opposite of phosphorylase a and b)
glycogen synthase is allosterically activated by…
glc and G6P
What does glycogen synthase (GSK) kinase do?
turns off glycogen synthase by phosphorylating it
What does insulin do to PKB?
insulin activates PKB, which turns off GSK, thus activating glycogen synthesis
common gluconeogenesis precursors:
lac, some amino acids, glycerol
where does the conversion of puryate to oxaloacetate take place?
in the mitochondria
Can pyr, oxa, NADH or PEP cross the mitochondria?
only pyr and pep can. Oxa and NADH cannot
How to overcome the problem of not having cytosolic NADH available for gluconeogenesis?
Depends on precursor used.
-If using lac–>glc, cytosolic NADH can be produced (no need for mitochondrial NADH):
NAD+ NADH
l l lac pyr ----->etc.etc.
-If using ala–>pyr–>–>glc, need a transport NADH from mitochondria.
ala–>pyr (enters mito)–>oxa–>mal (can cross membrane into cytosol)–>oxa–>PEP
