Gluconeogenesis Flashcards
GLUCONEOGENESIS
It is the process by which glucose molecules are produced from _______ precursors.
These include ____,___ amino acids, _____ part of fat and ______ derived from odd chain fatty acids
non-carbohydrate
lactate; glucogenic; glycerol
propionyl CoA
Gluconeogenesis occurs mainly in the _____, and to a lesser extent in the ______.
The pathway is partly _____ and partly _______.
liver
renal cortex
mitochondrial
cytoplasmic
Key Gluconeogenic Enzymes
- __________
- ___________
- ____________
- ________________
Pyruvate carboxylase
Phosphoenol pyruvate carboxy kinase
Fructose-1-6-bisphosphatase
Glucose-6-phosphatase
Gluconeogenesis is m a reversal of glycolysis.
F
Gluconeogenesis involves several enzymes of glycolysis, but it is not a reversal of glycolysis.
Pyruvate Carboxylase Reaction
Pyruvate in the _____ enters the _____.
Then, ________ of pyruvate to ______ is catalysed by a mitochondrial enzyme, pyruvate carboxylase . It needs the co-enzymes _____ and ____
cytoplasm
mitochondria
carboxylation; oxaloacetate
biotin and ATP.
Gluconeogenesis
The carboxylation of pyruvate takes place in mitochondria.
So, oxaloacetate is generated inside the mitochondria.
This oxaloacetate has to be transported from mitochondria to ______, because further reactions of gluconeogenesis are taking place in _____.
This is achieved by the ___________________.
cytosol
cytosol
malate aspartate shuttle
In malate aspartate shuttle
Oxaloacetate is first converted to ____, which traverses the membrane and reaches ____ where it is then re-converted to oxaloacetate.
Oxaloacetate may also be transported as aspartate formed by _____ of oxaloacetate.
malate ; cytoplasm
transamination
Malate dehydrogenase is present in both mitochondria and cytoplasm.
T/F
T
When alanine is the substrate for gluconeogenesis, the ____ shuttle predominantly operates, because ____ is also required in the cytoplasm for the gluconeogenesis to continue.
When lactate is the substrate for gluconeogenesis, the _____ shuttle operates, because sufficient _____ is available in the cytoplasm by the LDH reaction.
malate
NADH
aspartate
NADH
Phosphoenol Pyruvate Carboxy Kinase
In the cytoplasm, PEPCK enzyme then converts _______ to ______ by removing a molecule of ___.
____ donates the phosphate
oxaloacetate to phosphoenol pyruvate
CO2
GTP
Partial Reversal of Glycolysis
The phosphoenol pyruvate undergoes further reactions catalyzed by the glycolytic enzymes to form ______
fructose-1,6-bisphosphate
In gluconeogenesis
Fructose 1,6-bis-phosphate is then acted upon by _______ to form __________
fructose 1,6-bisphosphatase
fructose -6-phosphate.
Gluconeogenesis
The glucose 6-phosphate is hydrolysed to _______ by _________
free glucose
glucose-6-phosphatase.
Glucose-6-phosphatase is active in ______.
It is present in _____ and ______ to a lesser extent, but is absent in _____.
liver
kidney and intestinal mucosa
muscle
Energy Requirement of glyuconeogenesis
The reactions catalyzed by pyruvate carboxylase, phosphoenol pyruvate carboxy kinase and phospho glycerate kinase require ___ ATP each
so ___ ATPs are used by 1 pyruvate residue to produce ___ molecule of glucose; or ___ ATPs are required to generate ___ glucose molecule.
one
3
one-half
6
one
Lactate to glucose
The lactate formed in the muscle is transported to the _____ where _______ converts lactate to _______. The pyruvate enters the gluconeogenic pathway to form ____.
liver
lactate dehydrogenase
pyruvate
glucose
____________ Cycle aka Cahill Cycle
Glucose-Alanine
Glucose-Alanine Cycle (Cahill Cycle)
Alanine is transported to ____ where it is _____ to _____ and converted to glucose.
liver
transaminated
pyruvate
Glucose-alanine cycle is important in conditions of starvation
T/F
T
Alanine cycle is intimately related with ____ cycle
Cori’s
Propionyl CoA is formed from odd chain fatty acids and carbon skeleton of some amino acids. It is converted to _______.
It is a (minor or major?) source for glucose.
succinyl CoA
Minor
Even chain fatty acids can be converted to glucose
T/F
F
Even chain fatty acids cannot be converted to glucose
_______ is an activator of pyruvate carboxylase
_____ is an activator of Fructose-1,6-bisphosphatase
Acetyl CoA
Citrate
Gluconeogenesis is (enhanced or hindered ?) by ATP.
Enhanced
CORI’S CYCLE OR LACTIC ACID CYCLE
It is a process in which glucose is converted to lactate in the ____; and in the ____ this lactate is re-converted into glucose.
muscle
liver
In an actively contracting muscle, pyruvate is reduced to ______ which may tend to ____ in the muscle.
lactic acid
accumulate
The muscle cramps, often associated with strenuous muscular exercise, are thought to be due to ________
lactate accumulation
To prevent the lactate accumulation, body utilises Cori’s cycle.
This lactic acid from muscle diffuses into the ______. Lactate then reaches ____, where it is ____ to ____.
Thus, it is channelled to ______ pathway .
blood
liver
oxidized
pyruvate
gluconeogenesis
______ is the storage form of carbohydrates in the human body.
The major sites of storage are _____ and _____.
Glycogen
liver and muscle
The glycogen content of liver is (more or less?) than in the skeletal muscle
But the total quantity of muscle glycogen is (more or less?) than liver glycogen because of the ________
More
Less
larger muscle mass
When blood glucose level falls, (muscle or liver ?) glycogen is broken down and helps to maintain blood glucose level.
Liver
The function of muscle glycogen is to act as ______ for ______.
reserve fuel
muscle contraction
All the enzymes related to glycogen metabolism are located in the _______
cytoplasm
In glycogenolysis
_______ removes glucose as _________ from glycogen (phosphorolysis)
The _____ linkages in the glycogen are cleaved.
It removes glucose units one at a time.
Enzyme sequentially hydrolyses alpha-1,4 glycosidic linkages, till it reaches a glucose residue, ____ glucose units away from a branch point .
Glycogen phosphorylase
glucose-1-phosphate
alpha-1,4
3-4
Glycogen phosphorylase contains __________ as a prosthetic group.
pyridoxal phosphate (PLP)
Glycogen phosphorylase
cannot attack the ____ linkage at _____ point.
1,6
branch
If glycogen phosphorylase alone acts on a glycogen molecule, the final product is a highly branched molecule; it is called _____
limit dextrin.
Regulation of Muscle Glycogen Phosphorylase
Skeletal muscle glycogen is degraded only when the demand for ATP is (high or low?) . The regulation of glycogenolysis in skeletal muscle is by ______ and ____ released from sarcoplasmic reticulum. _____ has no effect on muscle glycogenolysis.
High
epinephrine and calcium
Glucagon
Debranching by bifunctional (two) Enzymes
Then a block of __ glucose residues ( ____ unit) are transferred from the branching point to another branch.
This enzyme is alpha-1,4 → _______.
Now the branch point is free.
Then __________ (debranching enzyme) can hydrolyse the remaining glucosyl unit held in alpha-1,6 linkage at the branch point
This glucose residue is released as free glucose.
At this stage, the ratio of glucose-1phosphate to free glucose is about __:__
The _______ and _______ will together convert the branch point to a linear one.
With the removal of the branch point, phosphorylase enzyme can proceed with its action.
3; trisaccharide
alpha-1,4 glucan transferase
alpha1,6- glucosidase
8:1.
transferase and alpha-1,6-glucosidase
In glycogenolysis
Phosphogluco mutase
Phosphorylase reaction produces _______ while debranching enzyme releases _____.
The glucose-1-phosphate is converted to _________ by ________
glucose-1phosphate
glucose
glucose-6-phosphate
phosphoglucomutase
In glycogenolysis
Next, hepatic _________ hydrolyses glucose-6-phosphate to glucose.
The free glucose is released to the ______
glucose-6-phosphatase
blood stream.
——— Lacks Glucose-6-phosphatase
Muscle
Muscle will release glucose to the blood stream
T/F
With reason
F
Muscle will not release glucose to the blood stream, because muscle tissue does not contain glucose-6-phosphatase.
Fate of glucose-6-phosphate in muscle
Instead, in muscle, glucose-6-phosphate undergoes glycolysis to produce ATP for muscle contraction.
In muscle, the energy yield from one glucose residue derived from glycogen is ____ ATP molecules
Why???
3
because no ATP is required for initial phosphorylation of glucose (step 1 of glycolysis).
