BIOC384 Module 9
(a) Why is it critical for maintaining flux through the metabolic pathway that NADH be oxidized to NAD+, and (b) how is that done under anaerobic conditions in human cells?
(a) NAD+ is required for the glyceraldehyde-3P dehydrogenase reaction; (b) by converting pyruvate to lactate.
Calculate the actual free energy change (deltaG) for a reaction under physiological conditions (37ºC) in which the standard free energy change deltaGº' is +5.5 kJ/mol and the measured mass action ratio (Q) is 0.001. Choose the correct answer from below.
-12.3 kJ/mol
2-phosphoglycerate(2PG) is converted to phosphoenolpyruvate (PEP) by the enzyme enolase. The standard free energy change(deltaGo') for this reaction is +1.7 kJ/mol. If the cellular concentrations are 2PG = 0.5 mM and PEP = 0.1 mM, what is the free energy change at 37 oC for the reaction 2PG ↔ PEP?
-2.4 kJ/mol
Calculate the standard free energy change (deltaGº') for the combined reactions in glycolysis converting 1,3-bisphosphoglycerate to pyruvate using values given in the lecture notes.
-43.9 kJ/mol
Which statements below describe three regulatory mechanisms in the glycolytic pathway?
-Fructose-1,6-bisphosphate is an allosteric activator of pyruvate kinase -Fructose-2,6-bisphosphate is an allosteric activator of phosphofructokinase-1 -ATP is an allosteric inhibitor of phosphofructokinase-1
What does glycolysis accomplish for the cell?
-Generates a small amount of ATP (2 ATP/glucose) which is critical under anaerobic conditions. -Generates pyruvate, a precursor to acetyl CoA, lactate, and ethanol (in yeast).
Why does lactase deficiency lead to the retention of lactose within the small intestine and prevent transport across the intestinal lumen?
-Lactose is a polar molecule and cannot cross the intestinal membrane without a transport protein. -Transport proteins in the intestinal lumen are specific for monosaccharides.
Which two of the following compounds are used to produce ATP by substrate-level phosphorylation in glycolysis?
1,3-bisphosphoglycerate; phosphoenolpyruvate
Predict how oxygen saturation would be affected if an individual has defective hexokinase enzymes.
2,3-BPG levels are reduced and oxygen binding increases.
Predict how oxygen transport is affected in individuals with a hexokinase deficiency as a result of decreased flux through the glycolytic pathway.
2,3-BPG levels are reduced leading to higher oxygen affinity and reduced oxygen transport to the tissues.
Which of the following best describes the relationship among a subunit of the protein, metal cofactors, and ligands?
A metal ion and ligand interact with the protein in locations proximal to one another.
The standard free energy change of phosphate hydrolysis is shown below for several molecules in the glycolytic pathway. MoleculeΔG˚' (kJ/mol) Phosphoenolpyruvate 61.9 1,3-Bisphosphoglycerate 49.4 ATP → ADP + Pi 30.5 Fructose-6-phosphate 15.9 Glucose-6-phosphate 13.8 Using concentrations of intermediates found in a cell, the phosphorylation of glucose using inorganic phosphate has ΔG' = 19.7 kJ/mol, while phosphoryl transfer from ATP (ATP investment) results in ΔG' = -34.5 kJ/mol. What does this tell you about the values of Q and Keq for the phosphorylation of glucose with and without energy investment from ATP?
Without ATP investment, Q > Keq, and with ATP investment Q < Keq.
Sucrose, maltose, and lactose are common dietary disaccharides. Their monosaccharide components are substrates for the glycolytic pathway, but some must participate in additional reactions before they can act as substrates for a glycolytic enzyme. As a result, all do not enter glycolysis at the same step. In muscle cells, which enzyme would act as the rate-limiting step to regulate entry of products from all three dietary disaccharides into glycolysis?
phosphofructokinase-1
List three ways in which flux is controlled through glycolysis.
regulation of glucokinase, PFK-1, and supply and demand of intermediates
For the following reaction A→ B, if at equilibrium > 0, what can be said about the directionality of the reaction?
strongly favored in the reverse direction
Individuals with a deficiency in the aldolase B enzyme have a condition known as hereditary fructose intolerance. The metabolic intermediate that accumulates in the liver as a result of this deficiency can have an indirect, activating effect on hepatic glucokinase. The blood glucose levels in these individuals
would be lower than normal due to the increased reaction rate of glucokinase.
Refer to the numbered reactions of glycolysis in the diagram above. Which two reactions involve substrate level phosphorylation? (put the numbers corresponding to these two reactions in the first and second boxes below, in numerical order from lowest to highest) Which two reactions require an input of energy in the form of ATP? (put the numbers corresponding to these two reactions in the third and fourth boxes below, in numerical order from lowest to highest)
Answer for blank #1: 1 Answer for blank #2: 3 Answer for blank #3: 7 Answer for blank #4: 10
Why is it critical to glucose homeostasis that glucokinase has a low affinity for glucose with regard to insulin release from the pancreas?
Because increased glucose concentrations in the blood lead to increased rates of metabolic flux through the glycolytic pathway, which is required for insulin release
Why is fructose toxic to liver cells, but not muscle cells, in individuals with a defect in the enzyme aldolase B?
Because liver cells, but not muscle cells, use up ATP converting fructose to fructose-1P, which cannot be further metabolized.
What are examples of glycolysis in everyday biochemistry?
Glycolysis is the sole source of ATP under anaerobic conditions which can occur in animal muscle tissue during intense exercise. Fermentation also relies on glycolysis which is a process that is used to make alcoholic beverages when yeast cells are provided glucose without oxygen
The two most common nutrative (caloric) sweeteners used in the manufacturing of food and beverages are sucrose and high-fructose corn syrup (HFCS). The latter is produced from corn syrup in a process that enzymatically converts a percentage of the glucose, which is the predominant sugar component, into fructose. HFCS used in most commercial food and beverage production is either 55% or 42% fructose. Why is HFCS preferred over corn syrup for sweetening beverages and processed foods?
HFCS is sweeter than corn syrup.
What are the key regulated enzymes in glycolysis?
Hexokinase, Phosphofructokinase-1, Pyruvate kinase
Which of the following statements best describes the effect of ADP on the activity of PFK-1?
High concentrations of ADP block the inhibitory effect of ATP by competing for the same allosteric site on PFK-1.
Lactose intolerance is a condition caused by a deficiency in the lactase enzyme. Individuals with this deficiency can experience unpleasant symptoms if they eat lactose-containing foods such as dairy products. The human gene for lactase is expressed at high levels in infants to aid in the digestion of lactose in breast milk; however, lactase expression normally declines in adults, with the notable exception of people of Scandinavian descent. What reaction is catalyzed by lactase?
Hydrolysis of lactose to produce glucose and galactose
In which situation is glycolysis alone likely to be a major contributor to ATP generation?
In erythrocytes
Name the following disaccharide using the common name and the descriptive nomenclature.
Lactose; Gal(β1→4)Glc
Phosphorylation of glucose requires 1 ATP. Can the reverse reaction be used for substrate-level phosphorylation?
No, phosphate hydrolysis of glucose-6-phosphate is not spontaneous enough to couple to ATP synthesis.
In glycolysis, fructose 1,6-bisphosphate is converted to two products with a standard free-energy change () of 23.8 kJ/mol. Under what conditions (encountered in erythrocytes) will the free-energy change () be negative, enabling the reaction to proceed to products?
The free-energy change will be negative when there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products.
What advantage is there to phosphoglycerate kinase having an open and closed configuration?
The induced-fit mechanism maximizes accessibility of active site without sacrificing hydrophobic environment.
What advantage is there to phosphoglycerate kinase having an open and closed protein configuration?
The induced-fit mechanism maximizes accessibility of active site without sacrificing hydrophobic environment.
Glucose and fructose are both C6H12O6. What is the structural difference between them?
Fructose is a five membered ring and glucose is a six membered ring.
What is the overall net reaction of glycolysis?
Glucose + 2NAD+ + 2ADP + 2 Pi → 2 pyruvate + 2NADH + 2H+ + 2ATP + 2H2O ΔGº' = -35.5 kJ/mol
Based on the structures of D-glucose and D-galactose (shown below), which one of the following statements is true?
Glucose and galactose are epimers of each other.
In which of the following glycolytic pathway reactions is ATP phosphoryl transfer energy required to drive the reaction in the forward direction?
Glucose → glucose-6-phosphate
Which of the following can enter glycolysis without additional reactions?
Both products from maltose after maltase treatment
Label the graph below to show the effect of high ATP, ADP, or fructose-2,6-bisphosphate on phosphofructokinase-1 (PFK-1) activity.
C, A, B
Mike has lactose intolerance and has to ingest commercial lactase in pill form before consuming milk products in order to avoid the unpleasant symptoms associated with this disorder. One day he noticed a classmate refusing a free sample of the new milkshakes sold in the campus cafe. His classmate, Jamal, explains that he has to avoid all milk products in his diet because he has galactosemia. Mike offers Jamal one of his lactase pills. Because both of their disorders are caused by consumption of milk products, he thinks Jamal should try lactase to see if it will allow him to try the milkshake. Should Jamal try the lactase pill to see if it will work?
Jamal should not follow Mike's advice. If Jamal ingests lactase along with the milkshake, it could cause harmful side effects.
Find all of the conditions listed on the left side that either stimulate or inhibit liver PFK-1 activity as listed on the right. Note that every condition should lead to stimulated or inhibited PFK-1 activity. 1. Liver PFK-1 activity is stimulated. 2. Liver PFK-1 activity is inhibited.
__2__ ATP is bound to both the catalytic site and the allosteric effector site. __1__ The conformational equilibrium is shifted toward increased amounts of the R state structure. __1__ Increased fructose-2,6-bisphosphate levels. __2__ The conformational equilibrium is shifted toward increased amounts of the T state structure. __2__ Increased citrate levels in the cell. __2__ Decreased fructose-2,6-bisphosphate levels. __1__ Low energy charge in the cell. __1__ Increased levels of both ADP and AMP. __1__ AMP is bound to the allosteric effector site and ATP is bound to the catalytic site. __2__ High energy charge in the cell.
Put the following glycolytic reactions in the correct order. Only 8 of the 10 reactions are listed, so the answer should be the relative order of the reactions. Note that the answer is graded as an "all or nothing" question, meaning the order must be correct to earn 1 point.
__4__Cleavage reaction converting a diphosphate sugar into two monophosphate metabolites. __8__Substrate level phosphorylation reaction generating a net yield in ATP for the glycolytic pathway. __5__A redox reaction utilizing inorganic phosphate and a coenzyme. __7__A dehydration reaction generating a high energy phosphorylated compound. __1__Phosphorylation reaction generating a hexose sugar. __3__Phosphorylation reaction converting a hexose monophosphate into a hexose bisphosphate. __6__A substrate level phosphorylation reaction generating the ATP needed to replace the ATP investment in stage 1. __2__An isomerization reaction converting an aldose sugar into a ketose sugar.
Select only one of the four identical subunits of the protein by clicking one of the green-outlined boxes next to a subunit listed along the bottom of the player. When the subunit is selected, it will be covered with green x's. Next, change the display of the selected subunit to ribbon structure by clicking the dropdown menu in the upper right corner and then clicking "Toggle Ribbon for selection" on the Display line. Click "Toggle CPK for selection" to remove the space-filling display. To remove the green x's, click "Clear Selection" on the Misc line. Determine the secondary structure(s) that is/are exhibited in this polypeptide.
both alpha helices and beta sheets
The standard free energy change of phosphate hydrolysis is shown below for several molecules in the glycolytic pathway. MoleculeΔG˚' (kJ/mol) Phosphoenolpyruvate 61.9 1,3-Bisphosphoglycerate 49.4 ATP → ADP + Pi 30.5 Fructose-6-phosphate 15.9 Glucose-6-phosphate 13.8 (A) Phosphorylation of glucose to produce glucose-6-phosphate has ΔG˚' =_____kJ/mol without the use of ATP.(B) Coupling phosphorylation with ATP hydrolysis gives ΔG˚' =_____kJ/mol.
a. 13.8 b. -16.7
If phosphofructokinase experienced a mutation that interfered with substrate binding, then what other enzyme is going to be most immediately impacted in terms of accessing substrate?
aldolase
What effect do elevated levels of ATP have on glycolysis?
decrease the affinity of PFK-1 for fructose-6-P and slow rate of the pathway
Which of the following best defines substrate-level phosphorylation?
direct transfer of a Pi to an ADP
An infant who obtains nourishment from milk and who has galactosemia is unable to convert
galactose-1-P to glucose-1-P.
The two most common nutrative (caloric) sweeteners used in the manufacturing of food and beverages are sucrose and high-fructose corn syrup (HFCS). The latter is produced from corn syrup in a process that enzymatically converts a percentage of the glucose, which is the predominant sugar component, into fructose. HFCS used in most commercial food and beverage production is either 55% or 42% fructose. Which enzyme can be used in the production of HFCS to convert glucose to fructose in a single step?
glucose isomerase
