Biochem Seminar 7

Digestion and absorption of carbohydrate involves all of the following EXCEPT: a. an acid stable amylase which acts in the stomach b. disaccharides in the intestine c. pancreatic amylase c. salivary amylase

a. an acid stable amylase which acts in the stomach

The fructose 6-phosphate kinase I is activated allosterically by ADP but inhibited by high ATP concentration according to the plot. Which of the following substances has the same regulatory effect on fructose 6- phosphate kinase I activity as ATP? a. citrate b. AMP c. fructose 6-phosphate d. fructose 2,6-bisphosphate e. glucose

a. citrate

The glycolytic enzyme characteristic for liver and beta-cells of the islets of langerhans in the pancreas is: a. glucokinase b. hexokinase c. pyruvate kinase d. phosphofructokinase

a. glucokinase

In mammals glucose-6-phosphate can be directly converted to: a. glucose b. pyruvate c. galactose d. fructose-1,6-bisphosphate

a. glucose

A medical student studying in the US develops hemolytic anemia after taking the oxidizing antimalarial drug pamaquine. This severe reaction is most likely due to: a. glucose-6-phosphate dehydrogenase deficiency b. phosphofructokinase I deficiency c. diabetes d. glycogen phosphorylase deficiency

a. glucose-6-phosphate dehydrogenase deficiency

The primary positive control of gluconeogenesis is exerted by: a. high acetyl CoA levels b. high fructose 2,6-bisphosphate c. low acetyl CoA levels d. low citrate levels e. low ATP levels

a. high acetyl CoA levels

The enzyme hexokinase is: a. is inhibited by glucose-6-phosphate b. usually found in liver c. uses fructose as a main substrate d. is found everywhere glucokinase is found

a. is inhibited by glucose-6-phosphate

Gluconeogenesis is the metabolic pathway of glucose synthesis from following substrate: a. lactate b. fatty acids c. CO2 and H2O d. ketone bodies

a. lactate

Glucokinase is present in: a. liver b. muscles c. brain d. adipose tissue e. all tissues

a. liver

Two important functions of the pentose phosphate pathway: a. producing NADPH and pentose phosphates b. producing ATP and pentose phosphates c. producing NADPH and removing pentose phosphates d. producing pentose phosphates and triose phosphates

a. producing NADPH and pentose phosphates

Carbohydrates (like starch) are digested by the following enzymes: a. salivary amylase and pancreatic alpha-amylase b. salivary amylase and pancreatic lipase c. pancreatic alpha-amylase and lipase d. pancreatic alpha-amylase and tripsin

a. salivary amylase and pancreatic alpha-amylase

Which phosphate esters of sugars ARE NOT intermediates of pentose phosphate pathway: a.fructose 1,6-bisphosphate b. sedoheptulose-7-phosphate c. erytrose-4-phosphate d. ribose-5-phosphate

a.fructose 1,6-bisphosphate

Which of the following glucose transporters is localized in liver: a. GLUT 1 b. GLUT 2 c. GLUT 3 d. GLUT 4

b. GLUT 2

The most significant role of the oxidative portion of the pentose phosphate pathway is the generation of: a. hexose monophosphate from free hexose b. NADPH c. NAD+ d. ATP from ADP and Pi

b. NADPH

The main purpose of pentose phosphate pathway is to produce: a. glucose b. NADPH and ribose-5-phosphate c. lactate d. ATP

b. NADPH and ribose-5-phosphate

In humans, glucose can be made from all of the following EXCEPT: a. lactate b. acetyl CoA c. pyruvate d. glycerol

b. acetyl CoA

How does the liver glucokinase enzyme differ from hexokinase? a. glucose-6-phosphate inhibits activity of glucokinase but not hexokinase b. glucokinase synthesis is induced by insulin while hexokinase synthesis is not affected by insulin c. glucokinase has higher affinity for glucose than hexokinase d. hexokinase reaction is irreversible while glucokinase reaction is reversible

b. glucokinase synthesis is induced by insulin while hexokinase synthesis is not affected by insulin

Which of the following is a target of the hormones glucagon and insulin for controlling flux through the glycolytic and gluconeogenic pathways? a. hexokinase b. phosphofructokinase-2 c. phosphotriose isomerase d. aldolase e. all of the above

b. phosphofructokinase-2

Which of the following supports gluconeogenesis? a. alpha-ketoglutarate + aspartate yields glutamate + oxaloacetate b. pyruvate + ATP + HCO yields oxaloacetate + ADP + P, +H c. acetyl CoA + oxaloacetate + H20 yields citrate + CoA

b. pyruvate + ATP + HCO yields oxaloacetate + ADP + P, +H

Glucagon and epinephrine, inhibit glycolysis and stimulate gluconeogenesis in the liver by increasing the conc of cAMP. This in turn activates cAMP-dependent protein kinase, leading to the phosphorylation and inactivation of: a. hexokinase b. pyruvate kinase c. glucokinase d. GLUT-4 transporter

b. pyruvate kinase

There are ____ irreversible reactions in glycolysis a. 1 b. 2 c. 3 d. 4

c. 3

The major rate-limiting step of glycolysis is the: a. conversion of glucose to glucose-6-phosphate b. conversion of glucose-6-phosphate to fructose-6-phosphate c. conversion of fructose-6-phosphae to fructose-1,6-bisphosphate d. aldolase reaction e. epimerase reaction

c. conversion of fructose-6-phosphae to fructose-1,6-bisphosphate

The absorption of glucose from the intestinal lumen into mucosal cells: a. does not require a carrier protein b. requires bile salts c. depends on the sodium ion gradient d. occurs through an insulin-responsive glucose transporter

c. depends on the sodium ion gradient

Muscle cells cannot release glucose to the blood, because these cells lack: a. glucokinase b. hexokinase c. glucose-6-phosphatase d. phosphofructokinase-2

c. glucose-6-phosphatase

What are three enzymatic steps in glycolysis that are bypassed with different enzymes in gluconeogenesis? a. phosphofructokinase, phosphoglycerate mutase, pyruvate kinase b. hexokinase, phosphofructokinase, phosphoglycerate kinase c. hexokinase, phosphofructokinase, pyruvate kinase d. phosphohexose isomerase, hexokinase, pyruvate kinase

c. hexokinase, phosphofructokinase, pyruvate kinase

Pyruvate kinase activity in liver is markedly decreases in untreated diabetes. The insulin treatment results in restoration of the enzyme activity to normal because: a. insulin is an allosteric activator of pyruvate kinase b. insulin promotes phosphorylation and activation of pyruvate kinase c. insulin promotes dephosphorylation and activation of pyruvate kinase d. insulin acts as cofactor of reaction catalyzed by pyruvate kinase

c. insulin promotes dephosphorylation and activation of pyruvate kinase

The transport of glucose across the cell membrane is stimulated by insulin in which of the following? a. heart b. intestinal mucosa c. liver d. adipose e. brain

c. liver

The disaccharide composed of glucose and fructose is digested by: a. lactase b. maltase c. sucrase d. amylase

c. sucrase

Which one of the following statements is FALSE? a. the reactions of the pentose phosphate pathway occur in the cytoplasm b. the metabolic cost of producing 12 equivalents of NADPH by the combined action of the oxidative and non-oxidative branches of the pentose phosphate is one equivalent of hexose phosphate c. the reactions of the pentose phosphate pathway enable to net production of ribose phosphates without the net consumption of any glycolytic intermediates

c. the reactions of the pentose phosphate pathway enable to net production of ribose phosphates without the net consumption of any glycolytic intermediates

Which of the following glucose transporters are localized in enterocytes: a. GLUT 1 and GLUT 2 b. GLUT 2 and GLUT 4 c. GLUT 3 and GLUT 5 d. GLUT 2 and GLUT 5

d. GLUT 2 and GLUT 5

Which of the following statements about the conversion of pyruvate to phosphoenolpyruate in gluconeogenesis is FALSE? a. it requires the net input of two equivalents of nucleotide triphosphate b. may occur with the net consumption of one molecule of NADH c. it is catalyzed by the enymes pyruvate carboxylase and phosphoenolpyruvate carboxykinase d. acetyl-CoA is an allosteric inhibitor of pyruvate carboxylase

d. acetyl-CoA is an allosteric inhibitor of pyruvate carboxylase

Gluconeogenesis requires: a. biotin b. bicarbonate c. ATP d. all of the above

d. all of the above

Disaccharides are digested in: a. stomach b. liver c. lumen of large intestine d. brush border of the small intestine

d. brush border of the small intestine

Tissues that strictly depend on glucose for their source of energy include: a. brain and kidney b. muscles and brain c. muscles and erythrocytes d. erythrocytes and brain

d. erythrocytes and brain

The phosphorylation of phosphofructo-2 kinase/ fructose-2,6 bisphosphatase: a. is caused indirectly by insulin and leads to the inactivation of phosphofructo-2-kinase and activation of fructose-2,6-bisphosphatase b. is caused indirectly by insulin and leads to the inactivation of fructosee-2,6-bisphosphatase and activation of phosphofructo-2-kinase c. is caused by a NADH/acetyl CoA activated kinase d. is caused indirectly by glucagon and leads to the inactivation of phosphofructo-2-kinase and of fructose-2,6-bisphosphatase

d. is caused indirectly by glucagon and leads to the inactivation of phosphofructo-2-kinase and of fructose-2,6-bisphosphatase

Deficiency of sucrase is accompanied by: a. low activity of lactase b. high activity of lactase c. low activity of maltase d. low activity of isomlatase

d. low activity of isomlatase

The enzyme phosphofructokinase I is: a. inhibited by ATP b. stimulated when the energy charge is low c. inhibited by citrate d. stimulated by fructose-2,6-bisphosphate e. all of the above

e. all of the above

Hexokinase is controlled primarily by: a. ATP concentration b. NADH concentration c. fructose-1,6 bisphosphate concentration d. fructose-2,6- bisphosphate concentration e. glucose-6-phosphate concentration

e. glucose-6-phosphate concentration

Which one of the following enzymes catalyzes phosphorylation of substrate (without ATP production) during glycolysis? a. pyruvate kinase b. phosphoglycerate kinase c. triose phosphate isomerase d. aldolase e. glyceraldehyde-3-phosphate dehydrogenase

e. glyceraldehyde-3-phosphate dehydrogenase

Glycolysis in RBCs produces: a. citrate b. GTP c. CO2 d. glucose-1-phosphate e. lactate and NADH

e. lactate and NADH

Which one of the following compounds is common to both the oxidative branch and the nonoxidative branch of the pentose phosphate pathway? a. xylulose-5-phosphate b. glucose-6-phosphate c. glyceraldehyde-3-phosphate d. fructose-6-phosphate e. ribulose-5-phosphate

e. ribulose-5-phosphate