BMS1030 - Glycogenolysis, Glycogenesis and Gluconeogenesis Flashcards
(23 cards)
What is Glycogenolysis? What is it also known as? What enzyme is involved?
The process of getting glucose from storage.
Glycogen Catabolism.
Key enzyme = Glycogen Phosphorylase
What is the difference between a-Amylase and glucosidases?
a-Amylase - hydrolyses bonds at end of polypeptide chains (1,4 linkages)
Glucosidases - hydrolyses bonds at branch points (1,6 linkages)
forming smaller sugars
What is glycogen broken down into? By what enzyme?
What is it then converted into? How does this affect ATP yield?
Units of Glucose 1-phosphate
By glycogen phosphorylase
Converted into glucose 6-phosphate and enters glycolysis.
(Extra 1 ATP molecule preserved per G-6-P as one investment stage skipped)
What enzyme converts Glucose 1-phosphate into Glucose 6-phosphate?
Phosphoglucomutase - adds a phosphate to position 6 and removes phosphate from position 1.
This makes it usable as it can now enter glycolysis.
What is Glycogenesis? What is the key enzyme is involved?
Forming 1->4 glycosidic bonds in glycogen.
Glycogen synthase
How does glycogenesis occur? What is it stimulated by?
Glycogenin protein forms the core of a glycogen particle.
The first glucose is linked to a tyrosine -OH
Glycogen synthase attaches glucose units one at a time to form a structure (like a hairy ball of string).
Stimulated by G-6-P and insulin.
Why can’t we store and break down glycogen at the same time?
Because what stimulates one process inhibits the other.
What is Gluconeogenesis? Why is it needed? Where does it occur?
The creation of new glucose.
Because very small/finite resources of glucose/glycogen in system.
Occurs in the liver.
What can gluconeogenesis form? What can it not form?
Can form: pyruvate, lactate, glycerol, AAs and all TCA intermediates
Cannot form: FAs - because FAs yield acetyl-CoA which cannot be converted back to pyruvate (irreversible step).
Why is gluconeogenesis not the reverse of glycolysis?
Because there are 3 irreversible steps that need to be bypassed.
Because the energetics of glycolysis mean you need to switch glycolysis off before turning on gluconeogenesis.
Ask Adam about formation of citrate and Pyruvate to Acetyl CoA slides.
Where does gluconeogenesis occur? What substrates cannot be used?
In the liver
Glucose created from many substrates but NOT fatty acids
In gluconeogeneis, which steps are the same (just in reverse) and which steps are replaced?
Steps 2 and 4-9 are the same.
Steps 1, 3 and 10 (the regulated steps) are replaced.
In gluconeogenesis, how is Pyruvate converted to PEP?
Via creating Oxaloacetate using Pyruvate carboxylase. And then converting Oxaloacetate to PEP using PEPCK enzyme.
Via a diversion into and out of the mitochondria.
In order for Oxaloacetate to cross the mitochondrial membrane, (from the matrix to cytosol) what occurs?
Oxaloacetate is converted to Malate (using an enzyme and NADH), carried across the membrane via a dicarboxylate carrier and then converted back into Oxaloacetate (using NAD+).
What does pyruvate carboxylase require?
ATP and bicarbonate as substrates
Biotin coenzyme
Acetyl CoA to activate it
High ATP and Acetyl CoA concentrations stimulate pyruvate to enter gluconeogenesis.
Lots of ______ is needed to drive the reaction of PEPCK (convertng Oxaloacetate to PEP). In what 2 ways is it provided?
GTP (equivalent to ATP) is hydrolyzed.
Decarboxylation is a favourable reaction.
In skeletal muscle, what does PEPCK allow for?
Storage of fatty acids as TGs - forming fat droplets which are used as energy reserves.
This creates a sustainable ATP supply to the working muscles.
Benefits = enhanced endurance, better weight management, appetite control and metabolic health.
In Gluconeogenesis, how is Fructose-1,6-bisphosphate converted to Fructose 6-Phosphate?
Using the enzyme Fructose-1,6-bisphosphatase
(the reaction in opposite direction using PKF1 and is irreversible)
What stimulates and inhibits Fructose-1,6-bisphosphatase enzyme? What kind of regulation is it?
GLUCAGON stimulates enzyme by decreasing fructose 2,6 bisphosphate.
ADRENALINE inhibits enzyme by increasing fructose 2,6 bisphosphate.
Allosteric regulation
- citrate
- fructose-2,6-bisphosphate
- AMP
What organs do not carry out gluconeogenesis?
Where is Glucose-6-phosphotase found? How is G-6-P hydrolyzed? How is glucose released?
Brain and muscle does not carry out gluconeogenesis (as don’t have the enzymes).
In the ER of liver and kidney cells
G-6-P is hydroyzed as it passes into the ER.
ER vesicles filled with glucose diffuse to plasma membrane, fuse with it and open releasing glucose into bloodsteam.
How is lactate converted back to glucose?
What is the cycle involved?
Lactate in muscle returned to liver and reoxidized to pyruvate by lactate dehydrogenase.
Pyruvate converted to glucose.
The Cori Cycle
