MCB 450 Homework 6

In contracting skeletal muscle, a sudden elevation of cytosolic Ca2+ concentration will result in: Activation of cAMP-dependent protein kinase. Dissociation of cAMP-dependent protein kinase into catalytic and regulatory subunits. Activation of phosphorylase kinase. Inactivation of phosphorylase kinase caused by the action of protein phosphatase. Conversion of cAMP to AMP by phosphodiesterase.

Activation of phosphorylase kinase.

Glycogen phosphorylase releases glucose units from glycogen in what state? As glucose 6-phosphate As glycerol As glucose 1-phosphate As fructose 1,6-bisphosphate As fatty acids

As glucose 1-phosphate

How does phosphorylation trigger specific catalytic function of proteins involved in signal cascades? Makes the receptor more likely to capture the signaling molecule Changes the electrical potential of the cell membrane Allows hydrophilic signaling molecules to cross the plasma membrane Changes the shape and thus the enzymatic activity of the proteins involved All of the above

Changes the shape and thus the enzymatic activity of the proteins involved

Given the following graph of the rate of PFK as a function of substrate concentration in the presence of two different effectors. Determine which of the two effectors has an inhibitory effect.

Effector 2

GAPDH function is hindered by the production of a thioester intermediate.

False

Glucose 6-phosphate is made in the extracellular space prior to transport into the cytoplasm.

False

Substrate-level phosphorylation is the phosphorylation of AMP by ATP.

False

When Ribose 5-phophate needs are greater than the need for NADPH, Glycolysis and the backwards route of the oxidative phase of PPP are used.

False

When muscle cells use glucose to generate ATP under aerobic conditions, NAD+ must be regenerated by converting pyruvate to lactate to sustain glycolysis.

False

The NADPH produced during the PPP is the reducing power for the synthesis of: Acetaldehyde Oxaloacetate Fumarate Fatty acids Lactate

Fatty acids

When night feedings are discontinued, an infant shows symptoms of lethargy, unconsciousness, convulsions and sweating. When a sample of liver taken from this infant is incubated with 14C-lactate, the 14C label is found in glucose, but not in glycogen. Galactose metabolism is normal. Which enzyme might be deficient? Glycogen synthase Triose isomerase Phosphoglucomutase UDP-glucose pyrophosphorylase Pyruvate kinase

Glycogen synthase

An adult male is given an injection of epinephrine after a bee sting. He has quickly become hyperglycemic. The most likely cause of high serum glucose is an increase in which of the following processes? Hepatic glycogenolysis Proteolysis of muscle to release amino acids for hepatic gluconeogenesis Lipolysis in adipose tissue, which in turn increases gluconeogenesis in the liver Increased glycolysis Absorption of carbohydrate from the GI tract

Hepatic glycogenolysis

Signaling of GPCRs (G-protein coupled receptors) is terminated by which mechanism? Hydrolysis of GTP (guanosine triphosphate) to GDP (guonosine diphosphate) by G-protein α. Cleavage of the GPCRs by receptor-specific serine or threonine proteases Hydrolysis of GTP to GDP by G-protein β Phosphorylation of receptors by cAMP (cyclic adenosine monophosphate) activated PKA (protein kinase A), which blocks the interaction with G-protein All of the above

Hydrolysis of GTP (guanosine triphosphate) to GDP (guonosine diphosphate) by G-protein α.

Which of the following would be associated with LOW glycolysis rate? Activation of protein kinase A Activation of phosphoprotein phosphatase Decreased cAMP levels Hypoxia Drinking soda (not the sugar-free kind) Low alanine levels Inactivation of PKA Exercise

Inactivation of protein kinase A

During Glucose 6-phosphate dehydrogenase activity, which reaction takes place? Lactonase opens the glucose ring. FAD is reduced. NADH donates hydride to G6P NADP+ is oxidized. NAD+ is reduced.

Lactonase opens the glucose ring.

In tissues deriving energy anaerobically (such as rapidly exercising skeletal muscle), lactate, rather than pyruvate, serves as the end product of glycolysis. Which of the following statements best explains why pyruvate is converted to lactate under these circumstances? Lactate activates PFK-1, thus stimulating glycolysis.NAD+necessary for the glyceraldehyde phosphate dehydrogenase reaction is regenerated.The conversion of pyruvate to lactate is accompanied by the production of ATP.Lactate, but not pyruvate, serves as a substrate for gluconeogenesis.

NAD+ necessary for the glyceraldehyde phosphate dehydrogenase reaction is regenerated.

Which of the following glycogen storage diseases affects only organs composed of lysosome rich cells? Parkinson's disease Anderson disease Pompe disease Von Gierke disease McArdle disease

Pompe disease

McCardle syndrome is due to a skeletal muscle deficiency of glycogen phosphorylase. Which of the following would be observed in such a patient with this syndrome? Skeletal muscle has high level of glycogen with shorter than normal branches Skeletal muscle has high level of glycogen with no branches Skeletal muscle has high level of glycogen with normal structure Skeletal muscle has abnormally low glycogen Fasting hypoglycemia

Skeletal muscle has high level of glycogen with normal structure

Steroid hormones regulate gene expression through which of the following mechanisms? Steroid hormones diffuse through the cell membrane and bind to cytoplasmic receptors, resulting in their nuclear translocation and binding to the hormone response elements. Steroid hormones diffuse through the cell membrane and activate protein kinase C. PKC then phosphorylates transcription factors, causing their binding to hormone response elements. Steroid hormones activate MAP kinases, which phosphorylate the steroid hormone receptor and stimulate its binding to the hormone response elements. Steroid hormones bind to the cell-surface receptor and induce the formation of cAMP, which then stimulates protein kinase A. PKA then phosphorylates transcription factors, causing their binding to hormone response elements. All of the above

Steroid hormones diffuse through the cell membrane and bind to cytoplasmic receptors, resulting in their nuclear translocation and binding to the hormone response elements.

Pyruvate kinase is a tetrameric enzyme that can exist as a L (found mostly in liver) or M (found mostly in muscles) forms. Which of the following statements comparing the L and M forms of pyruvate kinase is true? The L form is more likely to be phosphorylated when glucagon level is low. The L form is more likely to become phosphorylated under high blood sugar conditions. The M form is less susceptible to regulation by phosphorylation. The M form is more likely to become phosphorylated in the presence of high level of insulin. The M form is more phosphorylated when glucagon levels is high.

The M form is less susceptible to regulation by phosphorylation.

Which of the following statements concerning glycolysis is correct? Hexokinase is important in hepatic glucose metabolism only in the absorptive period following consumption of carbohydrate-containing meal. The conversion of glucose to lactate requires presence of oxygen. The conversion of glucose to lactate yields 2ATP and two NADH. The reactions take place in the matrix of the mitochondria. The reaction catalyzed by phosphofructokinase is inhibited by ATP.

The reaction catalyzed by phosphofructokinase is inhibited by ATP.

ATP is a co-substrate of the enzyme phosphofructokinase (PFK/PFK-1). In most species ATP is also an inhibitor of PFK-1 at higher concentrations. Which statement below would provide a suitable explanation for this discrepancy? There are two sites on PFK-1 that bind ATP. One is the active site; the other is the regulatory site where inhibition occurs. PFK-1 must be phosphorylated by ATP in the active site and the phosphorylated PFK-1 must be the less active form. ATP is unable to bind to the allosteric site on PFK at high concentration. ATP actually activates the reverse of the reaction preceding the PFK-1 step in the pathway. It likely has no direct effect on PFK-1.

There are two sites on PFK-1 that bind ATP. One is the active site; the other is the regulatory site where inhibition occurs.

A 50-yr-old man presented with symptoms of weakness, fatigue, and shortness of breath. His hemoglobin levels were low. Red blood cells isolated from the patient showed very low levels of lactate production. Which of the following enzyme deficiency could cause his anemic symptoms? Acetyl CoA carboxylase Pyruvate carboxylase Glucokinase Triosephosphate isomerase

Triosephosphate isomerase

A 15 year old boy visits his doctor complaining of abdominal cramps and diarrhea after drinking milk. The most likely cause of his problem is lack of small intestinal enzyme lactase.

True

Aldolase hydrolyzes Fructose 1,6 bisphosphate to produce glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.

True

During exercise, glycolysis is stimulated by a feed-forward stimulation of pyruvate kinase.

True

GAPDH uses NAD+ oxidize glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate.

True

In the phosphopentose isomerase reaction Ribulose 5-phosphate is converted to Ribose 5-phophate through an enediolate intermediate.

True

Phosphofructokinase-1 is the rate-limiting step of glycolysis.

True

The function of the thioester intermediate formed from glyceraldehyde 3-phosphate allows a two-step reaction to be coupled so that the second energetically unfavorable phosphorylation can occur.

True

Under anaerobic conditions, the net yield of one mole of glucose is (pick the BEST answer): Two moles of lactate and two moles of ATP. Two moles of lactate, two moles of NADH, and two moles of ATP. Two moles of lactate and six moles of ATP. One mole of pyruvate, two moles of NADH, and two moles of ADP. Two moles of pyruvate, two moles of NAD+, and two moles of ATP.

Two moles of lactate and two moles of ATP.