Chapter 14: Gluconeogenesis and PMP

the liver stores glycogen and releases glucose into the blood during time of need, i.e. when blood glucose levels fall lower than 5 mM, what would be the consequence if the KM were low?

a low Km indicates a higher binding affinity, meaning that even at low glucose levels glucose can still bind to its enzyme, allowing more glucose to be taken up by the liver, this could result in too much glucose being absorbed and glucose levels in the blood becoming too low

which of the following is NOT associated of the pentose monophosphate pathway? a. production of NADPH+H+ b. hydrolysis of ATP c. oxidation of glucose6P d. synthesis of sugar intermediates

b. hydrolysis of ATP

the enzyme glucose6P dehydrogenase catalyzes the first step in the pentose monophosphate pathway producing the products 6P gluconolactone and NADPH+H+, this enzyme _____________ (mark all that apply) a. controls the metabolic flux into glycolysis b. is inhibited by the levels of NADPH+H+ c. catalyzes a redox reaction d. uses glucose6P as a substrate

c. catalyzes a redox reaction d. uses glucose6P as a substrate

which molecules cannot be used as a precursor for gluconeogenesis? a. alanine b. pyruvate c. leucine d. oxaloacetate e. glutamate

c. leucine

which enzyme is not involved in gluconeogenesis? a. glucose 6-phosphatase b. PEP carboxykinase c. pyruvate decarboxylase d. fructose 1,6-bisphosphatase

c. pyruvate decarboxylase

the PMP is important for the processes listed below except for _______ a. detoxifying of oxygen radicals b. production of sugar intermediates c. synthesis of ribose-5P d. ATP synthesis e. production of NADPH+H+

c. synthesis of ribose-5P

which is not a special feature of glucokinase? a. high KM for glucose b. not inhibited by glc6P c. located in the liver d. sequestered in the nucleus

d. sequestered in the nucleus

why is lactate generated in the muscle during strenuous exercise?

during exercise there is a need for energy, to meet this need pyruvate is converted into lactate as a quicker means of generating ATP, lactate helps regenerate NAD+ from NADH allowing glycolysis to continue

what is the effect of elevated cytoplasmic glucose levels on hexokinase IV? high Fru6P?

elevated glucose levels will cause hexokinase IV to become more active since the glucose levels will cause the regulatory protein on hexokinase IV to dissociate, allowing it back into the cell high Fru6P will also cause feedback inhibition of hexokinase and force it back into the nucleus

the reaction of hexokinase and PFK-1 in glycolysis are considered irreversible, how are the "reversed" in glycolysis?

glucose-6-phosphatase catalyzes the dephosphorylation of glucose-6-phosphate to release free glucose and inorganic phosphate, this allows the regeneration of glucose from glucose-6-phosphate fructose-1,6-bisphosphatase catalyzes the dephosphorylation of fructose-1,6-bisphosphate to form fructose-6-phosphate

both, glycolysis, and gluconeogenesis take place in the cytoplasm, what would be the net result if these enzymes were functioning unregulated?

if these enzymes were functioning unregulated, it could lead to a futile cycle in which glycolysis and gluconeogenesis would be continually occurring at the same time, with the net result being the consumption of ATP and the production of heat without a net synthesis of glucose or energy

the reaction pyruvate + NADH + H+ -> lactate + NAD+ has ∆G⁰' = -23 kJ/mol, why is this reaction readily reversible in the liver but not in the muscle?

in the liver there are enzymes and metabolic pathways that facilitate the reverse reaction, where lactate can be converted back to pyruvate through gluconeogenesis, however, in the muscle glycolysis is the focus meaning the reaction is less favored, additionally the liver has a high concentration of LDH-B, which has a higher affinity for pyruvate

in the liver lactate is oxidized to pyruvate, this reaction has a ∆G⁰' = 23 kJ/mol, how can the reaction occur in the liver?

the oxidation of lactate to pyruvate is coupled with the reduction of NAD+ to NADH, which has a negative ∆G⁰' and is energetically favorable, additionally, lactate can be used as a substrate for gluconeogenesis, which is an energetically favorable process that occurs in the liver

what happens to Glucose6P when the cells have high levels of NADPH+H+?

under conditions of high NADPH levels, the feedback inhibition of G6PD redirects glucose-6-phosphate away from the oxidative phase of the pentose phosphate pathway, contributing to the cell's ability to balance its metabolic and redox needs based on the current cellular environment