Exam 3 Flashcards
In contrast to glycolysis, the pentose phosphate pathway allows the complete oxidation of glucose to CO2.
True.
When this occurs, the overall stoichiometry involves the input of 6 molecules of glucose-6-phosphate with the production of 12 NADPH, 6 CO2, and the regeneration of 5 molecules of glucose-6-phosphate.
The formation of DNA and RNA directly depends on high gluconeogenesis activity in the cell.
False.
High activity (especially in rapidly dividing cells) of the pentose phosphate pathway is required to supply ribose-5-phosphate for nucleotide biosynthesis.
Glucose 1-phosphate is the direct product of glycogenolysis.
True.
It is formed by the catalytic action of glycogen phosphorylase on glycogen.
Glycogen synthase catalyzes the linkage of all glucose molecules used in the formation of glycogen in live and muscle tissue.
False.
Glycogen synthase does not catalyze the formation of the alpha (1-6) linkages required for formation of branches. This is accomplished by the enzyme amylo (1,4 - 1,6) transglycosylase (the branching enzyme). In addition, glycogenin catalyzes primer extension.
Glycogen synthase catalyzes the joining of two glucose units, supplied as UDP-glucose, to initiate formation of a glycogen chain.
False.
Glycogen synthase requires an existing polymer of four to eight glucose residues as a primer.
Gluconeogenesis is simply a reversal of glycolysis that occurs when blood glucose levels fall below normal.
False.
While some reactions are reversals of glycolytic reactions, four different enzymes are required to bypass the three metabolically irreversible reactions of glycolysis.
The formation of one mole of glucose by gluconeogenesis from pyruvate requires the same amount of energy as that produced by glycolytic degradation of one mole of glucose to pyruvate.
False.
The conversion of two moles of pyruvate to one mole of glucose requires 6 moles of ATP. ATP or equivalent is required for the conversions of:
(a) pyruvate to oxaloacetate
(b) oxaloacetate to phosphoenolpyruvate
(c) 3-phosphoglycerate to 1,3-bisphosphoglycerate.
Each of these reactions is used twice to convert two pyruvates to one glucose.
The Cori cycle is a combination of glycolysis and gluconeogenesis occurring in different body tissues.
True.
It involves glycolysis in peripheral tissues and gluconeogenesis in the liver.
The enzymes that catalyze the reactions of the pentose phosphate pathway are all found in the cytosol.
True.
Since the pentose phosphate pathway works in conjunction with glycolysis, the most logical place for it to be located is in the cytosol.
The enzymes phosphfructokinase-1 and fructose 1,6-bisphosphatase form a substrate cycle.
True.
The interconversion of fructose-6-phosphate and fructose 1,6-bisphosphate in glycolysis and gluconeogenesis comprise a substrate cycle. Control over both of these enzymes is extremely important to prevent the wasteful use of energy in the cell.
Normally, the brain relies almost entirely on glucose for its energy needs.
True.
Hence, normal blood glucose levels are maintained at all times, even at the expense of peripheral (muscle) tissue.
Note: The brain does utilize ketone bodies during starvation.
Most glucose 6-phosphate produced in the liver from glycogenolysis is converted to free glucose for delivery to cells of other tissues.
True.
The glucose is delivered to brain cells, adipocytes, and erythrocytes.
Glucagon is a small peptide hormone that stimulates glycogenolysis by specifically targeting liver cells.
True.
Only liver cells are rich in glucagon receptors, thus the liver is targeted by glucagon.
In the liver, glucagon causes the activation of phosphofructokinase-2 which produced fructose 2,6-bisphosphate, an activator of phosphofructokinase-1 and inhibitor of fructose 1,6-bisphosphatase.
False.
Insulin would cause the activation of phosphofructokinase-2. Glucagon causes the activation of fructose 2,6-bisphosphate which removes fructose 2,6-bisphosphate, thus activating fructose 1,6-bisphosphatase and inhibiting phosphofructokinase-1.
The coenzyme required for reductive biosynthesis (e.g., of fatty acids), that is produced by the pentose phosphate pathway, is _________ .
NADPH
A pentose phosphate pathway enzyme that catalyzes the transfer of a three-carbon unit from a ketose-phosphate to an aldose-phosphate is called a/an __________ .
transaldolase
Name the pathway or process discussed in text Chapter 12 to which each of the following belongs:
pyruvate carboxylase _______________
ribose 5-phosphate _______________
glucose 6-phosphatase _______________
UDP-glucose _______________
gluconeogenesis
pentose phosphate pathway
gluconeogenesis or pentose phosphate pathway
glycogen synthesis
Glycogen phosphorylase catalyzes the degradation of glycogen chains from their nonreducing ends, but stops four glucose residues from a branch point. The remaining molecule is called a/an _____________ .
limit dextrin
Gluconeogenesis requires four enzymes that are not enzymes of the glycolytic pathway. These four enzymes are _____________, _____________, _____________, and _____________ .
pyruvate carboxylase
phosphoenolpyruvate carboxy kinase
fructose 1,6 bisphosphatase
glucose 6-phosphatase
The protein that is attached to the glycogen primer required for glycogen synthesis is called ____________ .
glycogenin
In mammals, the hormone _____________ activates glycogen degradation in the muscles while ___________ activates glycogen synthesis.
epinephrine; insulin
PEP carboxykinase is regulated by ______________ of the gene in response to increased cAMP levels that result from prolonged release of glucagon.
hormonal induction
Three major gluconeogenic precursors are ___________, which comes from anaerobic muscle, ____________, which comes from the breakdown of protein in peripheral tissue, and ___________, which comes from metabolism of triacylglycerols.
lactate
alalnine (and most other amino acids)
glycerol
A pair of reactions that both form and degrade a specific substrate, in order to fine tune regulation of metabolism, is called a ____________ .
substrate cycle