Wk 13 - Glycolysis and Gluconeogenesis ?'s
Assume that the substrate cycle that exists as shown undergoes reciprocal regulation such that the production of B is upregulated by 50% and the production of A is downregulated by 50%. What will be the next flux of B in this situation? 168 144 48 104
144 An increase in the production of B by 50% will increase flux from 120 to 180. A decrease in the production of A by 50% will decrease flux from 72 to 36. The net flux is the difference between the two: 180 − 36 = 144.
The affinity of glucokinase is approximately _____ hexokinase. 10 times higher than 50 times lower than 50 times higher than 10 times lower than
50 times lower than Glucokinase phosphorylates glucose only when glucose is abundant because the affinity of glucokinase for glucose is about 50-fold lower than that of hexokinase.
Assume that pyruvate is undergoing fermentation. If the carbonyl carbon adjacent to the methyl group of pyruvate is labeled with 14C, in which of the following is CORRECT? Lactate will be labeled at C-3. Acetaldehyde will be labeled at C-1. CO2 will be labeled. Acetaldehyde will be labeled at C-2. Lactate will be labeled at C-1.
Acetaldehyde will be labeled at C-2. C-3 is removed as carbon dioxide, leaving C-2 as the carbonyl carbon and C-1 in the methyl group.
Which of the following is NOT true of the structure of triose phosphate isomerase? Contains a structural motif called an alpha beta barrel. It contains histidine 95 and glutamate 165 as essential components of the active site. Contains a structural motif called a zinc finger. It has eight parallel β-strands at its core, surrounded by eight α-helices.
Contains a structural motif called a zinc finger. The structural motif found in triose phosphate isomerase is called an alpha beta barrel.
Despite being labeled as a GLUT, which of the following is primarily a fructose transporter? GLUT 4 GLUT 5 GLUT 2 GLUT 3
GLUT 5 GLUT5, present in the small intestine, functions primarily as a fructose transporter.
HIF-1 affects the expression of all of the following EXCEPT: GLUT2. hexokinase. PFK. VEGF.
GLUT2. HIF-1 increases the expression of GLUT1 and GLUT3.
The enzyme glucose 6-phosphatase is an important regulator of gluconeogenesis. All of the following are true EXCEPT: Glucose 6-phosphatase is sequestered away from the cytoplasm, where its substrate is produced. Glucose 6-phosphatase is present in most cells. If the T3 transporter associated with glucose 6-phosphatase were not functioning due to a mutation, blood glucose levels would drop. Glucose 6-phosphatase relies on the T1 transporter to supply its substrate.
Glucose 6-phosphatase is present in most cells. Most tissues lack glucose 6-phosphatase, and gluconeogenesis ends with glucose 6-phosphate, which is often then converted to glycogen for storage.
Which of the following describes what is happening in the first step? Glutamate 165 acts as a general base by abstracting a proton from carbon 1. Histidine 95, acting as a general acid, donates a proton to the oxygen atom bonded to carbon 2, forming the enediol intermediate. Histidine 95 acts as a general base by abstracting a proton to the oxygen atom bonded to carbon 2. Glutamate 165, acting as a general acid, donates a proton from carbon 1, forming the enediol intermediate. Histidine 95 acts as a general acid by donating a proton to carbon 1. Glutamate 165, acting as a general base, abstracts a proton to the oxygen atom bonded to carbon 2, forming the enediol intermediate. Glutamate 165 acts as a general acid by abstracting a proton from carbon 1. Histidine 95, acting as a general base, donates a proton to the oxygen atom bonded to carbon 2, forming the enediol intermediate.
Glutamate 165 acts as a general base by abstracting a proton from carbon 1. Histidine 95, acting as a general acid, donates a proton to the oxygen atom bonded to carbon 2, forming the enediol intermediate. Electrons from the carboxyl group of Glu 165 abstract the proton from carbon 1; bases are proton acceptors. His 95 donates a proton to dihydroxyacetone phosphate; proton donators are acids.
Scientists are studying an enzyme. As they add the enzyme's preferred substrate, the enzyme's side chains close around the substrate, leaving only a hydroxyl group of the substrate poking out. The enzyme then catalyzes the transfer of a phosphoryl group from ATP onto that hydroxyl group. What kind of enzyme is being studied? phosphatase mutase kinase dehydrogenase
Kinase Substrate-induced cleft closing is a general feature of kinase. Kinase catalyze the transfer of a phosphoryl group from ATP to an acceptor
What form of pyruvate kinase is phosphorylated by a glucagon-triggered cascade, and what affect does this have upon its activity? M; decreases L; increases L; decreases M; increases
L; decreases A glucagon-triggered cascade phosphorylates the L (liver) form of pyruvate kinase and decreases its activity when glucose levels are low. Muscle and brain are given preferential access to glucose.
Glucokinase is found in: liver stomach stomach and liver muscle
Liver Glucokinase is found in the liver and the pancreas
During glycolysis, phosphoenolpyruvate is converted to pyruvate in one step. In gluconeogenesis, it takes two steps to convert pyruvate back into phosphoenolpyruvate. The standard free energy change for the conversion of pyruvate directly to phosphoenolpyruvate would be +31 kJ/mol, but the two steps reduce the standard free energy change to +0.8 kJ/mol. What is the nature of the two steps used, and what is the effect upon the overall reaction? Pyruvate is decarboxylated and then carboxylated, resulting in a less exergonic reaction. Pyruvate is carboxylated and then decarboxylated, resulting in a less endergonic reaction. Pyruvate is decarboxylated and then carboxylated, resulting in a less endergonic reaction. Pyruvate is carboxylated and then decarboxylated, resulting in a less exergonic reaction.
Pyruvate is carboxylated and then decarboxylated, resulting in a less exergonic reaction. Pyruvate is first carboxylated to form oxaloacetate, then decarboxylated to form phosphoenolpyruvate. The overall reaction is less exergonic than a one step reaction would be, but the free energy is still positive, so it is not endergonic and requires ATP to take place.
You have isolated two isozymes of the enzyme from muscle and from liver that catalyze the following reaction: Glucose + ATP → glucose 6-phosphate + ADP In the excitement of your biochemical success, you forgot to label the tubes! You decide to perform some kinetics to help identify which enzyme is in which tube. Here is the Michaelis-Menten plot you make for the two enzymes. Given these data, which of the following is TRUE? The data shown in green must be the data for glucokinase. The data shown in green must be the data for the isozyme having the higher KM. The data shown in green represent an enzyme with a lower affinity for the substrates. The data shown in green must be the data for hexokinase.
The data shown in green must be the data for hexokinase. Glucokinase phosphorylates glucose only when glucose is abundant because the affinity of glucokinase for glucose is about 50-fold lower than that of hexokinase.
If iodine is added to a substance containing undigested starch, the substance will turn a blue-black color. You are given two solutions, one of which is amylase and the other which is an inactive substance, in containers labeled "enzyme one" and "enzyme two." How could you determine which enzyme is amylase? Using two samples of table sugar (glucose), add "enzyme one" to one sample and "enzyme two" to the other sample. The one that does not change color was treated with amylase. Using two small pieces of potato, soak one in "enzyme one" and the other in "enzyme two." Then add iodine to each sample. The piece that turns blue-black was treated with amylase. Using two pieces of fat, add "enzyme one" to one piece and "enzyme two" to the other piece. The piece that turns blue-black was treated with amylase. Using two pieces of bread, add "enzyme one" to one piece and "enzyme two" to the other piece. Then add iodine to each sample. The one that does not change color was treated with amylase.
Using two pieces of bread, add "enzyme one" to one piece and "enzyme two" to the other piece. Then add iodine to each sample. The one that does not change color was treated with amylase. Bread contains starch. Adding amylase to bread will cause the starch to break down, or be "digested." As a result, iodine added to the bread with amylase will not indicate starch, but iodine added to the bread with the inactive enzyme will still contain starch, and therefore will turn blue-black.
You have been given two different species of bacteria by your professor. You are told that both species are capable of consuming glucose but that one of the species lives by oxidation of glucose via glycolysis, the TCA cycle, and the electron transport chain and cannot survive under anaerobic conditions. Your job is to design an experiment to figure out which species is which. Which of the following experimental designs would generate results that would allow you to distinguish the two species? attempt to grow both organisms in the presence of oxygen with the idea that only one will grow in the presence of oxygen attempt to grow both organisms in the absence of oxygen with the idea that only one will grow in the absence of oxygen attempt to grow both organisms in the presence of oxygen with the idea that both could grow in the presence of oxygen attempt to grow both organisms in the absence of oxygen with the idea that both could grow in the absence of oxygen
attempt to grow both organisms in the presence of oxygen with the idea that both could grow in the presence of oxygen If grown in an aerobic environment, at least one of the organisms should be expected to live.
Which of the following might be an expected outcome following the addition of an inhibitor of protein kinase A (PKA)? inhibition of pyruvate kinase decreased responsiveness to glucagon inhibition of phosphofructokinase-2 increased phosphorylation of the bifunctional enzyme phosphofructokinase 2/fructose 2,6-bisphosphatase
decreased responsiveness to glucagon Glucagon is the hormone that stimulates protein kinase A and activates FBPase2 when blood glucose is scarce. This results in the stimulation of gluconeogenesis. The reverse process involves another hormone, insulin, which stimulates phosphoprotein phosphatase and PFK-2 when blood glucose is plentiful. This results in the stimulation of glycolysis.
What strategy is employed by the initial steps of glycolysis? form a compound that can be readily cleaved NAD+ regeneration transamination of glycolysis metabolites trap glucose in the cell by positively charging it
form a compound that can be readily cleaved The first few steps of glycolysis prepare glucose for cleavage into phosphorylated three-carbon units.
How many steps in the glycolytic pathway have ATP as either a reactant or a product? six five two three four
four ATP is a reactant in two steps of stage 1 of glycolysis, and it is a product in two steps during stage 2 of glycolysis.
Pyruvate kinase in muscle is stimulated by: fructose 1,6-bisphosphate. alanine. glucagon. −ATP.
fructose 1,6-bisphosphate. Fructose 1,6-bisphosphate allosterically stimulates pyruvate kinase.
If carried to completion, what does the gluconeogenic pathway ultimately convert pyruvate into? phosphoenolpyruvate glucose oxaloacetate glucose 6-phosphate
glucose Glucose is the final product of the gluconeogenesis pathway.
The hydrolysis of triacylglycerols in fat cells yields what molecule that can be converted into glucose? oxaloacetate glycerol acetyl CoA fatty acids
glycerol Glycerol can enter the gluconeogenesis pathway at the dihydroxyacetone phosphate step. The initial hydrolysis of triacylglycerols in fat cells yields glycerol and fatty acids, but only glycerol is usable by gluconeogenesis.
The first step in glycolysis is catalyzed by the enzyme _____ and involves glucose and _____ as substrates. phosphofructokinase; NAD+ hexokinase; ATP hexokinase; NAD+ phosphofructokinase; ATP
hexokinase; ATP Glucose is phosphorylated by hexokinase; the phosphate group comes from an ATP molecule.
All of the following enzymes are involved in glycolysis at some point. Given the sequential reactions in the pathway, which answer lists the first four enzymes in the correct order (without skipping any steps)? glyceraldehyde 3-phosphate dehydrogenase; phosphoglycerate kinase; enolase hexokinase; phosphoglucose isomerase; phosphofructokinase; aldolase phosphoglycerate mutase; phosphoglycerate kinase; pyruvate kinase hexokinase; phosphoglucose isomerase; aldolase; triose phosphate isomerase
hexokinase; phosphoglucose isomerase; phosphofructokinase; aldolase Hexokinase catalyzes step 1 of glycolysis and is followed by the catalysis of phosphoglucose isomerase, phosphofructokinase, and aldolase respectively.
Acidification of a tumor environment does all of the following EXCEPT: inhibits CD8+T. impedes tumor invasion. is observed even in noninvasive leukemias. inhibits NK.
impedes tumor invasion. Acidification facilitates tumor invasion.
The glucokinase regulatory protein in the liver _____ the enzyme when blood glucose levels are _____. stimulates; low stimulates; high inhibits; low inhibits; high
inhibits; low When glucose levels are limited, glucokinase regulatory protein inhibits glucokinase so that glucose can be provided to the brain and muscle.
The isozyme of hexokinase that functions in aerobic glycolysis: is not affected by glucose 6-phosphate. is inhibited by ATP. binds to lysosomes. is affected by pyruvate kinase. L
is affected by pyruvate kinase. L Pyruvate kinase M is expressed during aerobic glycolysis.
Glucokinase is found in: liver stomach stomach and liver muscle
liver Glucokinase is found in the liver and the pancreas.
GLUT4 transporters are found in: small intestine. muscle and fat cells. all cells. liver and pancreas.
muscle and fat cells. GLUT4 is found in muscle and fat cells. It transports glucose into muscle and fat cells.
HIF-1 is activated by a lack of: glucose. ATP. oxygen. pyruvate.
oxygen. Hypoxia-inducible transcription factor (or HIF-1) is activated by a lack of oxygen; the word hypoxia means a lack of oxygen. HIF-1 signals the growth of new blood vessels to carry more oxygen to the oxygen-deficient area.
The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate is carried out by fructose 1,6-bisphophatase during gluconeogenesis. Which enzyme catalyzes the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate during glycolysis? phosphofructokinase triose phosphate isomerase (TPI) phosphohexose isomerase fructose 1,6-bisphosphatase
phosphofructokinase Phosphofructokinase catalyzes the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate. This is the "committed step" of glycolysis.
Which enzyme is negatively regulated by ATP and citrate, and which enzyme is inhibited by ATP without citrate? hexokinase; enolase pyruvate carboxylase; pyruvate kinase pyruvate kinase; enolase phosphofructokinase; pyruvate kinase
phosphofructokinase; pyruvate kinase High levels of ATP signal that there is plenty of energy and inhibit phosphofructokinase. Citrate is also an indicator that the cell has plenty of energy, as it is a metabolite in the citric acid cycle, the cycle that follows glycolysis. ATP and alanine inhibit pyruvate kinase.
Salma has recently given birth. Shortly after birth, her baby had a seizure. Analysis of the infant's blood showed low blood glucose and high levels of lactic acid. Salma's baby most likely has: pyruvate carboxylase deficiency (PCD) niacin deficiency triose phosphate isomerase deficiency (TPID) galactose 1-phosphate uridyl transferase deficiency
pyruvate carboxylase deficiency (PCD) Pyruvate carboxylase deficiency is characterized by hypoglycemia and lactic acidosis. Symptoms include lethargy and seizures.
Which of the following enzymes is a main point of metabolic control in glycolysis? phosphoenolpyruvate carboxykinase pyruvate carboxylase phosphoglycerate kinase pyruvate kinase
pyruvate kinase Pyruvate kinase catalyzes the third irreversible step in glycolysis, making it a main point of metabolic control along with the other two enzymes that catalyze irreversible steps, phosphofructokinase and hexokinase.
A baker adds yeast and warm water to bread to cause it to rise. What other ingredient of bread is necessary for this to occur, and what is the by-product being produced that causes the bread to rise? sugar, carbon dioxide flour, formate flour, ethanol sugar, lactate
sugar, carbon dioxide Sugar is digested by the yeast, producing carbon dioxide and ethanol. The ethanol evaporates, but the carbon dioxide is trapped by the gluten in the flour, causing the bread to rise as it expands.
Lactate is usually removed from muscle cells by a(n) _____ that also transports _____. antiporter; Ki symporter; H+ symporter; K+ antiporter; H+
symporter; H+ Lactate and H+ leave the cell together, a type of transport called symport; the prefix "sym-" means "together" or "with." The production of lactate in the cell causes a drop in pH. Higher acidity is caused by increased H+ ions in the cell; therefore it is necessary to remove these excess ions in order to maintain a healthy pH.
Phosphofructokinase 2/fructose 2,6-bisphosphatase (PFK2/FBPase2) is expressed primarily in which type of tissue? skeletal muscle the liver cardiac muscle the brain
the liver When glucose is high, fructose 2,6-bisphosphatase stimulates phosphofructokinase-1, promoting glycolysis. Glycolysis takes place in the liver, as does most of gluconeogenesis.
Aerobic glycolysis increase in tumor cells leads to the formation of more intermediates for what pathway that generates biosynthetic reducing power? glycolysis the pentose phosphate pathway fatty acid metabolism the citric acid cycle
the pentose phosphate pathway The pentose phosphate pathway metabolizes glucose 6-phosphate.
Which enzyme of glycolysis is the only one whose deficiency is lethal? pyruvate kinase triose phosphate isomerase phosphofructokinase phosphoglucose isomerase
triose phosphate isomerase Triose phosphate isomerase deficiency is rare and the only lethal glycolytic enzymopathy. This deficiency is characterized by severe hemolytic anemia and neurodegeneration.
Kayla's toddler Liam is finally walking, but his walking is very wobbly and he seems to be unable to build any muscle. Kayla took him to the doctor. Tests revealed that Liam has a deficiency of red cells due to lysis, is suffering from inflammation of the heart and progressive neuromuscular disorder, and has an excessive amount of dihydroxyacetone phosphate is his cells. Liam most likely has: galactose 1-phosphate uridyl transferase deficiency niacin deficiency pyruvate carboxylase deficiency (PCD) triose phosphate isomerase deficiency (TPID)
triose phosphate isomerase deficiency (TPID) Triose phosphate isomerase deficiency has symptoms that include hemolytic anemia and progressive neuromuscluar disorder.
HIF-1 is activated in which of the following? exercise, diabetes diabetes, cataracts cataracts, tumor growth tumor growth, exercise
tumor growth, exercise Tumor growth and exercise both cause an oxygen deficit, or hypoxic environment.
Glucose 6-phosphate does NOT inhibit the dominant form of hexokinase in which tissues? tumors brain liver muscle
tumors Hexokinase in tumor cells is not susceptible to feedback inhibition by its product, glucose 6-phosphate.
