Harper's Biochemistry Chapter 20 - The Pentose Phosphate Pathway PDF

Question Answer What are the two major functions of the pentose B) Formation of NADPH and synthesis of ribose phosphate pathway? Explanation: The pentose phosphate pathway primarily functions to form NADPH f...

Question Answer What are the two major functions of the pentose B) Formation of NADPH and synthesis of ribose phosphate pathway? Explanation: The pentose phosphate pathway primarily functions to form NADPH for A) Formation of ATP and synthesis of proteins fatty acid and steroid synthesis and to synthesize ribose for nucleotide and nucleic B) Formation of NADPH and synthesis of ribose acid formation. C) Breakdown of fatty acids and synthesis of glucose D) Production of lactate and synthesis of amino acids E) Formation of glycogen and synthesis of cholesterol What is the consequence of a genetic deficiency in B) Hemolytic anemia glucose-6-phosphate dehydrogenase? Explanation: A deficiency in glucose-6-phosphate dehydrogenase, the first enzyme A) Hyperglycemia of the pentose phosphate pathway, leads to acute hemolysis of red blood cells, B) Hemolytic anemia resulting in hemolytic anemia. C) Essential pentosuria D) Hereditary fructose intolerance E) Galactosemia Which pathway is responsible for the synthesis of B) Uronic acid pathway glucuronic acid? Explanation: The uronic acid pathway synthesizes glucuronic acid, which is A) Glycolysis significant for the conjugation and excretion of metabolites and foreign chemicals as B) Uronic acid pathway glucuronides. C) Citric acid cycle D) Beta-oxidation E) Gluconeogenesis What is the dietary requirement for humans due to the B) Vitamin C lack of one enzyme in the uronic acid pathway? Explanation: Humans lack the enzyme gulonolactone oxidase in the uronic acid A) Vitamin D pathway, which explains why ascorbic acid (vitamin C) is a dietary requirement for B) Vitamin C humans but not for most other mammals. C) Vitamin B12 D) Vitamin A E) Vitamin K Which metabolic diseases are associated with B) Essential fructosuria, hereditary fructose intolerance, and galactosemia deficiencies in the enzymes of fructose and galactose Explanation: Deficiencies in the enzymes of fructose and galactose metabolism lead metabolism? to metabolic diseases such as essential fructosuria, hereditary fructose intolerance, A) Diabetes and hyperlipidemia and galactosemia. B) Essential fructosuria, hereditary fructose intolerance, and galactosemia C) Phenylketonuria and maple syrup urine disease D) Hyperthyroidism and hypothyroidism E) Cystic fibrosis and sickle cell anemia What is the end product of the complete oxidation of C) Carbon dioxide and water glucose in the pentose phosphate pathway? Explanation: The complete oxidation of glucose in the pentose phosphate pathway A) Lactate results in the formation of carbon dioxide and water, along with the generation of B) Pyruvate NADPH. C) Carbon dioxide and water D) Ethanol E) Acetyl-CoA Where do the reactions of the pentose phosphate C) Cytosol pathway occur? Explanation: The enzymes of the pentose phosphate pathway are cytosolic, meaning A) Mitochondria that the reactions occur in the cytosol of the cell. B) Nucleus C) Cytosol D) Endoplasmic reticulum E) Golgi apparatus Which molecule acts as the hydrogen acceptor in the C) NADP+ oxidative phase of the pentose phosphate pathway? Explanation: Unlike glycolysis, the pentose phosphate pathway uses NADP+ as the A) NAD+ hydrogen acceptor during the oxidative phase. B) FAD C) NADP+ D) ATP E) ADP What is the end product of the oxidative phase of the B) Ribose-5-phosphate pentose phosphate pathway? Explanation: In the first phase of the pentose phosphate pathway, A) Glucose-6-phosphate glucose-6-phosphate undergoes dehydrogenation and decarboxylation to yield B) Ribose-5-phosphate ribose-5-phosphate. C) Fructose-6-phosphate D) Glyceraldehyde-3-phosphate E) Pyruvate Which enzymes are primarily involved in the B) Transketolase and Transaldolase nonoxidative phase of the pentose phosphate Explanation: The nonoxidative phase of the pentose phosphate pathway involves a pathway? series of reactions primarily catalyzed by the enzymes transketolase and A) Hexokinase and Phosphofructokinase transaldolase. B) Transketolase and Transaldolase Question Answer C) Pyruvate kinase and Lactate dehydrogenase D) Glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase E) Aldolase and Enolase What is the main function of NADPH produced in the D) Reductive biosynthesis and antioxidant defense pentose phosphate pathway? Explanation: NADPH produced in the pentose phosphate pathway is crucial for A) Energy production reductive biosynthesis reactions and maintaining the antioxidant defense system of B) Synthesis of nucleotides the cell. C) Oxidative phosphorylation D) Reductive biosynthesis and antioxidant defense E) Glycolysis Which enzyme catalyzes the dehydrogenation of C) Glucose-6-phosphate dehydrogenase glucose-6-phosphate to 6-phosphogluconolactone in Explanation: Glucose-6-phosphate dehydrogenase is the NADP-dependent enzyme the oxidative phase of the pentose phosphate that catalyzes the dehydrogenation of glucose-6-phosphate to pathway? 6-phosphogluconolactone in the oxidative phase of the pentose phosphate A) Gluconolactone hydrolase pathway. B) 6-Phosphogluconate dehydrogenase C) Glucose-6-phosphate dehydrogenase D) Ribulose-5-phosphate 3-epimerase E) Transketolase What is the role of gluconolactone hydrolase in the B) It hydrolyzes 6-phosphogluconolactone pentose phosphate pathway? Explanation: Gluconolactone hydrolase is the enzyme responsible for hydrolyzing A) It catalyzes the dehydrogenation of 6-phosphogluconolactone to 6-phosphogluconate in the pentose phosphate glucose-6-phosphate pathway. B) It hydrolyzes 6-phosphogluconolactone C) It converts ribulose-5-phosphate to ribose-5-phosphate D) It catalyzes the formation of sedoheptulose-7-phosphate E) It is involved in the synthesis of PRPP Which enzyme requires NADP+ as a hydrogen C) 6-Phosphogluconate dehydrogenase acceptor in the second oxidative step of the pentose Explanation: 6-Phosphogluconate dehydrogenase is the enzyme that requires phosphate pathway? NADP+ as a hydrogen acceptor in the second oxidative step of the pentose A) Glucose-6-phosphate dehydrogenase phosphate pathway, leading to the formation of ribulose-5-phosphate. B) Gluconolactone hydrolase C) 6-Phosphogluconate dehydrogenase D) Transaldolase E) Ribose-5-phosphate ketoisomerase What is the final product of the oxidative phase of the C) Ribulose-5-phosphate pentose phosphate pathway? Explanation: The final product of the oxidative phase of the pentose phosphate A) Ribose-5-phosphate pathway is ribulose-5-phosphate, which is formed after the decarboxylation of B) Fructose-6-phosphate 6-phosphogluconate. C) Ribulose-5-phosphate D) Xylulose-5-phosphate E) Glyceraldehyde-3-phosphate Which enzyme is an isoenzyme of A) Hexose-6-phosphate dehydrogenase glucose-6-phosphate dehydrogenase found in the Explanation: Hexose-6-phosphate dehydrogenase is an isoenzyme of endoplasmic reticulum? glucose-6-phosphate dehydrogenase that is found in the endoplasmic reticulum. A) Hexose-6-phosphate dehydrogenase B) Gluconolactone hydrolase C) 6-Phosphogluconate dehydrogenase D) Transketolase E) Ribulose-5-phosphate 3-epimerase What is the role of 11-β-hydroxysteroid B) It catalyzes the reduction of cortisone to cortisol dehydrogenase-1 in the body? Explanation: 11-β-hydroxysteroid dehydrogenase-1 catalyzes the reduction of A) It converts glucose to glycogen inactive cortisone to active cortisol in the liver, nervous system, and adipose tissue. B) It catalyzes the reduction of cortisone to cortisol C) It synthesizes ribose-5-phosphate D) It oxidizes NADPH to NADP+ E) It converts ribose to ribulose Which enzyme converts ribulose-5-phosphate to C) Ribose-5-phosphate ketoisomerase ribose-5-phosphate? Explanation: Ribose-5-phosphate ketoisomerase converts ribulose-5-phosphate to A) Transaldolase ribose-5-phosphate, which is used for nucleotide and nucleic acid synthesis. B) Ribulose-5-phosphate 3-epimerase C) Ribose-5-phosphate ketoisomerase D) Glucose-6-phosphate dehydrogenase E) Fructose 1,6-bisphosphatase Question Answer What coenzymes are required for the transketolase C) Mg2+ and thiamin diphosphate reaction? Explanation: The transketolase reaction requires Mg2+ and thiamin diphosphate A) NAD+ and FAD (vitamin B1) as coenzymes. B) ATP and ADP C) Mg2+ and thiamin diphosphate D) Coenzyme A and biotin E) NADPH and riboflavin Which tissues have high activity of the pentose B) Liver, adipose tissue, and adrenal cortex phosphate pathway? Explanation: The pentose phosphate pathway is active in tissues such as the liver, A) Skeletal muscle and non-lactating mammary gland adipose tissue, and adrenal cortex, which specialize in reductive syntheses. B) Liver, adipose tissue, and adrenal cortex C) Heart and kidney D) Pancreas and spleen E) Bone marrow and cartilage What is the main difference between the pentose C) The pentose phosphate pathway produces CO2 phosphate pathway and glycolysis? Explanation: The pentose phosphate pathway is markedly different from glycolysis A) Both pathways produce ATP as it produces CO2 and utilizes NADP+ instead of NAD+, and does not generate ATP. B) Both pathways utilize NAD+ C) The pentose phosphate pathway produces CO2 D) Glycolysis produces NADPH E) Both pathways are identical How does the pentose phosphate pathway protect B) By generating NADPH for the reduction of oxidized glutathione erythrocytes against hemolysis? Explanation: In red blood cells, the pentose phosphate pathway is the sole source of A) By producing ATP NADPH, which is used for the reduction of oxidized glutathione catalyzed by B) By generating NADPH for the reduction of oxidized glutathione reductase, protecting against hemolysis. glutathione C) By synthesizing ribose-5-phosphate D) By converting glucose to glycogen E) By producing CO2 What enzyme catalyzes the removal of H2O2 in B) Glutathione peroxidase erythrocytes? Explanation: Glutathione peroxidase, which contains the selenium analog of A) Glutathione reductase cysteine (selenocysteine) at its active site, catalyzes the removal of H2O2 in B) Glutathione peroxidase erythrocytes. C) Catalase D) Superoxide dismutase E) Peroxidase What is the primary product of the uronic acid B) Glucuronic acid pathway in the liver? Explanation: The uronic acid pathway in the liver catalyzes the conversion of glucose A) Glucose to glucuronic acid, which is a precursor of proteoglycans and conjugated B) Glucuronic acid glucuronides. C) Fructose D) Ribose E) Lactose Why can't humans synthesize ascorbic acid? B) Absence of l-gulonolactone oxidase A) Lack of glucose-6-phosphate dehydrogenase Explanation: Humans and some other species cannot synthesize ascorbic acid due to B) Absence of l-gulonolactone oxidase the absence of the enzyme l-gulonolactone oxidase. C) Deficiency in NADPH D) Inability to metabolize fructose E) Lack of UDPGlc dehydrogenase What is the metabolic consequence of high fructose C) Increased fatty acid synthesis and VLDL secretion intake? Explanation: High fructose intake leads to increased fatty acid synthesis, A) Increased ATP production esterification of fatty acids, and secretion of very-low-density lipoprotein (VLDL), B) Decreased fatty acid synthesis which may raise serum triacylglycerols and LDL cholesterol concentrations. C) Increased fatty acid synthesis and VLDL secretion D) Reduced glycolysis E) Decreased LDL cholesterol levels Which enzyme catalyzes the phosphorylation of C) Fructokinase fructose to fructose-1-phosphate? Explanation: Fructokinase in the liver, kidney, and intestine catalyzes the A) Glucokinase phosphorylation of fructose to fructose-1-phosphate. B) Hexokinase C) Fructokinase D) Aldolase B E) Triokinase What is the primary fate of much of the fructose A) Conversion to glucose metabolized in the liver? Explanation: Fructose is primarily metabolized in the liver where it undergoes A) Conversion to glucose gluconeogenesis, leading to the production of glucose. B) Conversion to fat Question Answer C) Conversion to protein D) Conversion to glycogen E) Conversion to amino acids How does fructose-1-phosphate affect dietary glucose B) It activates glucokinase entry into the liver? Explanation: Fructose-1-phosphate activates glucokinase, thereby amplifying A) It inhibits glucokinase dietary glucose entry into the liver. B) It activates glucokinase C) It inhibits hexokinase D) It activates hexokinase E) It inhibits glucose-6-phosphatase What can the rapid phosphorylation of fructose in the A) Decrease in ATP and increase in ADP and AMP liver lead to? Explanation: The rapid entry and phosphorylation of fructose in the liver consume A) Decrease in ATP and increase in ADP and AMP ATP quickly, leading to a rise in ADP and AMP levels. B) Increase in ATP and decrease in ADP and AMP C) Increase in glucose levels D) Decrease in glucose levels E) Increase in glycogen storage What is a potential consequence of increased AMP in C) Conversion to hypoxanthine and uric acid the liver due to fructose metabolism? Explanation: Increased AMP in the liver can be converted to hypoxanthine and then A) Increased glycogen storage to uric acid, which can potentially cause gout. B) Increased protein synthesis C) Conversion to hypoxanthine and uric acid D) Increased fat synthesis E) Decreased glucose production Why do extrahepatic tissues generally not metabolize C) Glucose inhibits the phosphorylation of fructose much fructose? Explanation: In extrahepatic tissues, hexokinase catalyzes the phosphorylation of A) They lack hexokinase most hexose sugars, including fructose, but glucose inhibits this process as it is a B) They lack glucokinase better substrate for hexokinase. C) Glucose inhibits the phosphorylation of fructose D) They lack ATP E) They lack ADP What enzyme is responsible for the secretion of C) Aldose reductase sorbitol into the fetal blood in ungulates and whales? Explanation: Aldose reductase, found in the placenta of the ewe, is responsible for A) Hexokinase the secretion of sorbitol into the fetal blood. B) Glucokinase C) Aldose reductase D) Sorbitol dehydrogenase E) Xanthine oxidase What enzyme converts sorbitol into fructose in the D) Sorbitol dehydrogenase liver? Explanation: Sorbitol dehydrogenase in the liver, including the fetal liver, is A) Hexokinase responsible for converting sorbitol into fructose. B) Glucokinase C) Aldose reductase D) Sorbitol dehydrogenase E) Xanthine oxidase What is galactose needed for in the body? A) Synthesis of lactose, glycolipids, proteoglycans, and glycoproteins A) Synthesis of lactose, glycolipids, proteoglycans, Explanation: Galactose is essential for the synthesis of lactose, glycolipids, and glycoproteins proteoglycans, and glycoproteins, which are important components in various B) Synthesis of DNA and RNA biological processes. C) Production of hemoglobin D) Formation of muscle fibers E) Synthesis of cholesterol How is galactose derived in the body? B) From the hydrolysis of lactose A) From the hydrolysis of starch Explanation: Galactose is derived from the intestinal hydrolysis of lactose, which is B) From the hydrolysis of lactose the sugar found in milk. C) From the breakdown of proteins D) From the digestion of fats E) From the synthesis of amino acids Which enzyme catalyzes the phosphorylation of B) Galactokinase galactose? Explanation: Galactokinase catalyzes the phosphorylation of galactose, using ATP as A) Hexokinase the phosphate donor. B) Galactokinase C) Glucokinase D) Fructokinase E) Aldolase B What is the role of UDPGal 4-epimerase in galactose B) It converts UDPGal to UDPGlc Question Answer metabolism? Explanation: UDPGal 4-epimerase catalyzes the conversion of UDPGal to UDPGlc, A) It converts galactose to glucose involving oxidation and reduction at carbon 4 with NAD+ as a coenzyme. B) It converts UDPGal to UDPGlc C) It phosphorylates galactose D) It hydrolyzes lactose E) It synthesizes lactose Which enzyme catalyzes the synthesis of lactose in the A) Lactose synthase mammary gland? Explanation: Lactose synthase catalyzes the condensation of UDPGal with glucose to A) Lactose synthase yield lactose in the mammary gland. B) Galactokinase C) Hexokinase D) Glucokinase E) Aldolase A What are the major amino sugars mentioned in the A) Glucosamine, galactosamine, and mannosamine text? Explanation: The major amino sugars mentioned are glucosamine, galactosamine, A) Glucosamine, galactosamine, and mannosamine and mannosamine, which are important components of glycoproteins, B) Glucose, fructose, and galactose glycosphingolipids, and glycosaminoglycans. C) Ribose, deoxyribose, and xylose D) Sucrose, maltose, and lactose E) Alanine, glycine, and serine What is the principal sialic acid found in human A) N-acetylneuraminic acid (NeuAc) tissues? Explanation: The principal sialic acid found in human tissues is N-acetylneuraminic A) N-acetylneuraminic acid (NeuAc) acid (NeuAc), which plays a crucial role in various biological functions. B) Glucosamine C) Galactosamine D) Mannosamine E) Sialyltransferase What is the primary consequence of B) Erythrocyte hemolysis glucose-6-phosphate dehydrogenase deficiency in Explanation: Glucose-6-phosphate dehydrogenase deficiency impairs the generation erythrocytes? of NADPH, leading to oxidative stress and erythrocyte hemolysis, also known as A) Increased glucose production hemolytic anemia. B) Erythrocyte hemolysis C) Enhanced oxygen transport D) Decreased ATP production E) Increased fatty acid synthesis Which population is most commonly affected by C) Mediterranean and Afro-Caribbean glucose-6-phosphate dehydrogenase deficiency? Explanation: Genetic defects of glucose-6-phosphate dehydrogenase are common in A) Northern European populations of Mediterranean and Afro-Caribbean origin. B) East Asian C) Mediterranean and Afro-Caribbean D) Native American E) South Asian What is the relationship between C) It confers resistance against malaria glucose-6-phosphate dehydrogenase deficiency and Explanation: The distribution of mutant genes for glucose-6-phosphate malaria? dehydrogenase parallels that of malaria, suggesting that being heterozygous for the A) It increases susceptibility to malaria deficiency confers resistance against malaria. B) It has no effect on malaria C) It confers resistance against malaria D) It causes malaria E) It is only found in malaria-endemic regions What triggers hemolytic crises in individuals with B) Oxidative stress from infection, drugs, or fava beans glucose-6-phosphate dehydrogenase deficiency? Explanation: Hemolytic crises in individuals with glucose-6-phosphate A) High protein diet dehydrogenase deficiency are triggered by oxidative stress from infection, certain B) Oxidative stress from infection, drugs, or fava drugs like primaquine and sulfonamides, or consumption of fava beans. beans C) Excessive exercise D) High carbohydrate intake E) Dehydration What is the role of NADPH in erythrocytes? C) It reduces organic peroxides and H2O2 A) It is used for ATP synthesis Explanation: NADPH is crucial in erythrocytes for reducing organic peroxides and B) It is involved in DNA replication H2O2, which is part of the body's defense against lipid peroxidation. C) It reduces organic peroxides and H2O2 D) It transports oxygen E) It synthesizes hemoglobin What is the clinical significance of essential C) It is benign with no clinical consequences pentosuria? Explanation: Essential pentosuria is a rare benign hereditary condition where A) It causes severe metabolic acidosis considerable quantities of xylulose appear in the urine, but it has no clinical Question Answer B) It leads to chronic kidney disease consequences. C) It is benign with no clinical consequences D) It results in severe hypoglycemia E) It causes neurological deficits What enzyme deficiency leads to essential B) Xylulose reductase pentosuria? Explanation: Essential pentosuria is caused by a lack of xylulose reductase, the A) Glucose-6-phosphate dehydrogenase enzyme necessary to reduce xylulose to xylitol. B) Xylulose reductase C) Hexokinase D) Lactase E) Phosphoglucomutase What is the effect of aminopyrine and antipyrine on B) Increase in excretion of xylulose pentosuric subjects? Explanation: Aminopyrine and antipyrine increase the excretion of xylulose in A) Increase in glucose conversion to glucuronate pentosuric subjects, which is a notable effect on their metabolism. B) Increase in excretion of xylulose C) Decrease in fructose metabolism D) Increase in ATP synthesis E) Decrease in uric acid formation What can result from loading the liver with fructose? B) Hypercholesterolemia A) Hypotriacylglycerolemia Explanation: Loading the liver with fructose can lead to hypercholesterolemia due to B) Hypercholesterolemia increased fatty acid and triacylglycerol synthesis and VLDL secretion. C) Decreased VLDL secretion D) Increased ATP synthesis E) Decreased uric acid formation What condition is caused by a lack of hepatic B) Essential fructosuria fructokinase? Explanation: A lack of hepatic fructokinase causes essential fructosuria, which is a A) Hyperuricemia benign and asymptomatic condition. B) Essential fructosuria C) Gout D) Hypertriacylglycerolemia E) Alimentary pentosuria What is a potential consequence of high oral doses of B) Osmotic diarrhea fructose? Explanation: High oral doses of fructose may lead to osmotic diarrhea due to its A) Increased ATP synthesis absorption mechanism in the small intestine. B) Osmotic diarrhea C) Decreased uric acid formation D) Hypocholesterolemia E) Decreased fatty acid synthesis What is the result of fructose entering glycolysis via B) Bypassing the regulatory step catalyzed by phosphofructokinase fructokinase? Explanation: Fructose enters glycolysis via fructokinase, resulting in A) Increased regulation by phosphofructokinase fructose-1-phosphate that bypasses the regulatory step catalyzed by B) Bypassing the regulatory step catalyzed by phosphofructokinase. phosphofructokinase C) Decreased fatty acid synthesis D) Increased ATP synthesis E) Decreased VLDL secretion What characterizes hereditary fructose intolerance? B) Profound hypoglycemia and vomiting after fructose consumption A) Hyperglycemia and weight gain Explanation: Hereditary fructose intolerance is characterized by profound B) Profound hypoglycemia and vomiting after fructose hypoglycemia and vomiting after the consumption of fructose or sucrose, which consumption yields fructose upon digestion. C) Increased appetite and energy levels D) High blood pressure and dizziness E) Muscle cramps and dehydration What is a consequence of fructose 1,6-bisphosphatase B) Fructose-induced hypoglycemia despite high glycogen reserves deficiency? Explanation: Fructose 1,6-bisphosphatase deficiency leads to fructose-induced A) Increased ATP production hypoglycemia despite the presence of high glycogen reserves because B) Fructose-induced hypoglycemia despite high fructose-1-phosphate and 1,6-bisphosphate allosterically inhibit liver glycogen glycogen reserves phosphorylase. C) Enhanced liver function D) Decreased uric acid levels E) Improved glucose tolerance What accumulates in the lens of the eye in diabetic B) Fructose and sorbitol patients, potentially leading to cataracts? Explanation: Both fructose and sorbitol are found in increased concentrations in the A) Glucose and sucrose lens of the eye in diabetic patients and may be involved in the pathogenesis of B) Fructose and sorbitol diabetic cataract. C) Lactose and maltose D) Galactose and ribose Question Answer E) Mannose and xylose Which enzyme is responsible for reducing glucose to B) Aldose reductase sorbitol in the polyol pathway? Explanation: Aldose reductase is the enzyme responsible for reducing glucose to A) Glucokinase sorbitol in the polyol pathway, which is involved in the formation of fructose from B) Aldose reductase glucose. C) Hexokinase D) Phosphofructokinase E) Pyruvate kinase What condition results from the inability to B) Galactosemia metabolize galactose? Explanation: Galactosemia is a condition resulting from the inability to metabolize A) Diabetes mellitus galactose, which may be caused by inherited defects of galactokinase, uridyl B) Galactosemia transferase, or 4-epimerase. C) Hyperlipidemia D) Hypothyroidism E) Phenylketonuria What is the primary function of the pentose B) NADPH production to maintain glutathione in the reduced state phosphate pathway in erythrocytes? Explanation: In erythrocytes, the pentose phosphate pathway's major function is to A) ATP production provide NADPH to maintain glutathione in the reduced state, which is crucial for B) NADPH production to maintain glutathione in the preventing hemolysis. reduced state C) Ribose synthesis for nucleotide production D) Fatty acid synthesis E) Protein synthesis What is the role of the uronic acid pathway? C) Source of glucuronic acid for conjugation of substances A) Synthesis of amino acids Explanation: The uronic acid pathway is the source of glucuronic acid, which is used B) Production of ATP for the conjugation of many endogenous and exogenous substances before C) Source of glucuronic acid for conjugation of excretion as glucuronides in urine and bile. substances D) Breakdown of fatty acids E) Synthesis of cholesterol What is the main regulatory step in glycolysis that B) Phosphofructokinase fructose bypasses? Explanation: Fructose bypasses the main regulatory step in glycolysis catalyzed by A) Hexokinase phosphofructokinase, which stimulates liver glucose uptake, fatty acid synthesis, B) Phosphofructokinase and hepatic triacylglycerol secretion. C) Pyruvate kinase D) Glucokinase E) Aldolase