Biochemistry : Regulating Carbohydrate Synthesis
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Example Questions
Example Question #1245 : Biochemistry
When would you expect glycogen synthase to be activated?
When glucagon is in high concentration
When protein kinase A is activated
When there is a low concentration of glucose in the blood
When glycogen synthase is phosphorylated
When protein phosphatase I is activated
When protein phosphatase I is activated
Glycogen synthase is turned on when unphosphorylated. The enzyme responsible for this is protein phosphatase I. Protein kinase A inactivates glycogen synthase. Low glucose concentration causes a release in glucagon, which activates glycogen phosphorylase and deactivates glycogen synthase.
Example Question #1251 : Biochemistry
Which of the following is an oxidoreductase?
Hexokinase
Lactate dehydrogenase
Glucose 6-phosphatase
Aspartate amino-transferase
Trypsin
Lactate dehydrogenase
An oxidoreductase catalyzes the transfer of electrons from one molecule to the other, usually using 
Example Question #1 : Carbohydrate Synthesis
Given that the pyruvate dehydrogenase complex is product-inhibited, which of the following molecules would act as an inhibitor to it?
Acetyl-CoA
Phosphoenolpyruvate
Pyruvate
Acetyl-CoA
The pyruvate dehydrogenase complex catalyzes the following reaction:
Since it is product inhibited, acetyl-CoA will inhibit the complex.
Example Question #2 : Regulating Carbohydrate Synthesis
In gluconeogenesis, how can the reaction carried out by pyruvate kinase be reversed?
Pyruvate carboxylate converts pyruvate to oxaloacetate, which is converted by PEP carboxykinase into phosphoenolpyruvate (PEP)
A phosphatase can be used to dephosphorylate pyruvate into phosphoenolpyruvate (PEP)
PEP carboxykinase converts pyruvate to phosphoenolpyruvate (PEP)
Pyruvate kinase carries out a reversible reaction, and no other enzymes are needed
Pyruvate carboxylate converts pyruvate to oxaloacetate, which is converted by PEP carboxykinase into phosphoenolpyruvate (PEP)
There are 3 enzymes in glycolysis that carry out irreversible reactions: phosphofructokinase-1 (PFK-1), hexokinase and pyruvate kinase. While phosphatases are used to reverse the reactions for PFK-1 and hexokinase, they are not used in reversing the pyruvate kinase reaction. 2 enzymes are needed to convert pyruvate back into phosphoenolpyruvate (PEP). First, pyruvate carboxylase converts pyruvate into oxaloacetate, and then PEP carboxykinase converts this into PEP.
Example Question #2 : Carbohydrate Synthesis
What is the name of the enzyme that is found in the liver that converts glucose into glucose-6-phosphate?
Phospholipase
Glycogenin
Fructokinase
Glucokinase
Glycogen synthase
Glucokinase
Fructokinase catalyzes the reaction of fructose converting into fructose-1-phosphate. Glycogenin acts as a primer for glycogen synthesis, by polymerizing the first few molecules of glucose. Glycogen synthase converts glucose to glycogen. Phospholipase hydrolyzes phospholipids.
Example Question #4 : Carbohydrate Synthesis
What is the name of the process involved in the conversion of glucose to glycogen?
Glycolysis
Krebs cycle
Gluconeogenesis
Glucogenolysis
Glycogenesis
Glycogenesis
The process of glycogenesis is when glucose is converted into glycogen. This occurs in the muscle and the liver after food is consumed. Gluconeogenesis is the process where glucose is produced from non-carbohydrate precursors. Glycogenolysis is the breakdown of glycogen. Glycolysis is the breakdown of glucose into two molecules of pyruvate. The Krebs cycle does not generate glycogen or glucose, rather it produces high energy electrons to be carried to the electron transport chain for ATP production.
Example Question #3 : Carbohydrate Synthesis
Which reaction occurs during a fasting state when glycogen stores are depleted?
Gluconeogenesis
Krebs cycle
Glycolysis
Citric acid cycle
Electron transport chain
Gluconeogenesis
Glyconeogenesis occurs in the hepatic pathway when no glucose is available. The electron transport chain occurs during cellular respiration. Glycolysis is the break down of glucose, not the production of glycogen. The Krebs cycle and citric acid cycle are the same thing, and both are used to produce NADH and ATP.
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