Metabolic Pathway Integration Flashcards
When blood glucose is abnormally high, the pancreas releases:
(a) adrenaline.
(b) glucagon.
(c) glucose.
(d) insulin.
(e) trypsin
D
When blood glucose is abnormally low, the pancreas releases:
(a) adrenaline.
(b) glucagon.
(c) glucose.
(d) insulin.
(e) trypsin
B
The largest energy store in a well-nourished human is:
(a) ATP in all tissues.
(b) blood glucose.
(c) liver glycogen.
(d) muscle glycogen.
(e) triacylglycerols in adipose tissue
E
The principle target tissues of insulin include
(a) skeletal muscle.
(b) liver.
(c) adipose tissue.
(d) brain
(e) (a), (b) and (c) only
E
Glucose 6-phosphate is an intermediate in which of the following processes?
(a) Gluconeogenesis
(b) Glycolysis
(c) Fatty acid synthesis
(d) Glycogenolysis
(e) Both (a) and (b) are correct
W
In glycolysis moles of NADH are produced per mole of glucose consumed.
(a) 1
(b) 2
(c) 3
(d) 4
(e) 5
B
The conversion of acetyl CoA to malonyl CoA is inhibited by _____
(a) glucagon
(b) adrenaline
(c) palmitoyl-CoA
(d) All of the above are correct.
(e) None of the above are correct
D
Adrenaline triggers an increased rate of glycolysis in muscle by:
(a) activation of hexokinase.
(b) activation of phosphofructokinase-1.
(c) conversion of glycogen phosphorylase a to glycogen phosphorylase b.
(d) inhibition of the Cori Cycle.
(e) the Pasteur effect
B
Glucokinase:
(a) acts in the conversion of liver glycogen to glucose 1-phosphate.
(b) converts fructose-6-phosphate to glucose-6-phosphate
(c) converts glucose 6-phosphate to fructose 6-phosphate.
(d) is a hexokinase isozyme found in liver hepatocytes.
(e) is found in all mammalian tissues
D
The _____ is the site of most gluconeogenesis in mammals.
(a) liver
(b) pancreas
(c) cytosol of all cells
(d) small intestine
(e) kidney
A
Which of the following statements about metabolism in the mammalian liver is false?
(a) Most plasma lipoproteins are synthesized in the liver.
(b) The enzymatic complement of liver tissue changes in response to changes in the diet.
(c) The liver synthesizes most of the urea produced in the body.
(d) The presence of glucose 6-phosphatase makes liver uniquely able to release glucose into the bloodstream.
(e) Under certain conditions, most of the functions of the liver can be performed by other organs
E
Gluconeogenesis shares some, but not all, enzymes with the glycolytic pathway. It would appear to be more efficient if both pathways used all of the same enzymes since the pathways
are essentially the reverses of each other. Why don’t both pathways use all of the same enzymes?
(a) The reactions where enzymes differ occur in different parts of the cell for glycolysis versus gluconeogenesis.
(b) Enzymes can catalyse a reaction only in one direction, so naturally the two pathways have some enzymes that differ.
(c) In tissues where gluconeogenesis occurs, the glycolytic enzymes are present at extremely low concentrations.
(d) Three of the reaction steps in gluconeogenesis would have prohibitively large, positive free energies if they used glycolytic enzymes for their catalysis.
(e) The mechanism underpinning reciprocal regulation emphasises the concept of intelligent design
D
Under starvation conditions, about how long does it take in humans for the body to deplete the glycogen store in the liver?
(a) approx. 1 minute
(b) approx. 1 hours
(c) approx. 24 hours
(d) approx. 1 week
(e) approx. 1 month
C
Acetyl CoA is derived from _____
(a) glucose 6-phosphate.
(b) acetoacetate.
(c) alanine.
(d) fatty acids.
(e) pyruvate.
(f) all of the above options are correct
F
What hormone or enzyme activates the GLUT4 protein to facilitate transport glucose into cells?
(a) adrenaline
(b) insulin
(c) protein kinase A
(d) PFK-2
(e) glucagon
B
Glucagon is excreted when blood glucose is (high, low), while insulin is secreted when blood glucose is (high, low).
(a) high; high
(b) high; low
(c) low; low
(d) low; high
(e) none of the above are correct
D
Which of the options is an acceptable concentration for glucose in the blood of a normal individual?
(a) 5 μM
(b) 5 mM
(c) 50 mM
(d) 0.2 g/dL
(e) (b) and (d) are correct
B
Which of the following tissues can produce glucose by gluconeogenesis?
I. kidney
II. liver
III. adipose tissue
IV. muscle
V. brain
(a) I, II, III, IV, V
(b) I, II, IV, V
(c) I, II
(d) II, IV
(e) II only
C
The maturation of insulin from its precursor (preproinsulin) involves
(a) acetylation.
(b) oxidation.
(c) phosphorylation.
(d) proteolysis.
(e) reduction
D
Which of the following metabolic conversions provides the maximum rate of ATP production (mmol/sec) for muscle contraction?
(a) conversion of muscle glycogen to CO2
(b) conversion of muscle glycogen to lactate
(c) conversion of creatine phosphate to creatine
(d) conversion of fatty acid to CO2
(e) conversion of ketone bodies to acetyl CoA
C
Which of the following is TRUE regarding pancreatic β cells?
(a) Insulin is secreted by the β cells in response to the increase in β cell glucose receptor binding.
(b) Glucagon is secreted by the β cells in response to the increase in β cell glucose receptor binding.
(c) Insulin is secreted by the β cells in response to high glucose levels.
(d) Insulin is secreted by the β cells in response to low glucose levels.
(e) Glucagon is secreted by the β cells in response to high glucose levels
C
Which of the following are effects of insulin secretion?
I. Muscle and adipose tissue are stimulated to take up glucose.
II. Glycogen synthesis increases in the liver.
III. Gluconeogenesis is inhibited in the liver and kidney.
IV. Lipolysis increases in the adipose tissue.
(a) I, II
(b) I
(c) I, II, III
(d) I, III
(e) II, IV
C
Having a high blood glucose level is called _____.
(a) hyperglycemia
(b) diabetic ketoacidosis
(c) hypoglycemia
(d) macrosomia
(e) normoglycemia
A
Which of the following metabolic processes is promoted by insulin?
(a) catabolism of muscle protein
(b) fatty acid oxidation
(c) gluconeogenesis
(d) glycogenesis
(e) lipolysis
Answer (d)
The primary hormonal effects of insulin are the conversion of carbon energy into storage molecules. These actions include the incorporation of glucose into glycogen and the activation of lipogenesis pathways to increase the synthesis of triglycerides
During fasting, what role does gluconeogenesis play?
(a) Aids in the release of glucose from stored glycogen in the liver.
(b) Uses alanine and other amino acids to restore blood glucose levels.
(c) Produces products that slow the oxidation of pyruvate.
(d) Helps transport glucose across the blood-brain barrier to maintain brain glucose levels.
(e) All of the above options are correct
B
What is the earliest step in the insulin signalling pathway?
(a) Activation of Akt/protein kinase B (Akt/PKB)
(b) Activation of mitogen activated protein (MAP) kinase
(c) Tyrosine phosphorylation of internal domain sites of the insulin receptor
(d) Specific binding of insulin to its high-affinity plasma membrane receptors
(e) Recruitment of Insulin Receptor Substrate (IRS)-1
D
Compare in general terms the effects of adrenalin, glucagon, and insulin on glucose metabolism
Adrenalin and glucagon cause an increase in the blood glucose level.
Adrenalin acts when a higher than normal level of glucose is required; glucagon acts when the level is unusually low. Both stimulate gluconeogenesis and glycogen breakdown and decrease
glycolysis (except adrenaline in muscle) and glycogen synthesis. Insulin causes a decrease in blood glucose levels; it acts by increasing glycogen synthesis, glycolysis, and glucose uptake by cells as well as by decreasing glycogen breakdown
Describe five possible fates for glucose 6-phosphate in the liver
Possible answers include:
(1) conversion to liver glycogen;
(2) dephosphorylation and release of glucose into bloodstream;
(3) oxidation via the pentose phosphate pathway;
(4) oxidation via glycolysis and the citric acid cycle;
(5) oxidation to acetyl-CoA, which then serves as precursor for synthesis of triacylglycerols, phospholipids, and cholesterol
What is the major fuel for resting muscle and what is the major fuel for muscle under strenuous work conditions?
Fatty acids are the major fuel for resting muscle cells.
Glucose is the major fuel under strenuous exercise
Explain why insulin is required for adipocytes to synthesize triacylglycerols from fatty acids
Insulin promotes the uptake of glucose via the increase in GLUT4 receptors on the adipocyte surface. A source of glucose is necessary to supply the glycerol-3-phosphate backbone of triacylglycerols
After several days of starvation, the capacity of the liver to metabolize acetyl-CoA via the TCA cycle is greatly diminished. Explain
During starvation, the synthesis of glucose from liver oxaloacetate depletes the supply of TCA cycle intermediates and thus decreases the ability of the liver to metabolize acetyl-CoA via the TCA cycle
What metabolic changes occur during the early fasting state?
In the initial hours after a meal, the blood-glucose levels start to decrease, the insulin decreases, and glucagon is secreted by the α–cells of the pancreas. Glucagon stimulates the liver to mobilize glycogen stores, blocks glycogen synthesis, and inhibits fatty acid synthesis. Glucagon also stimulates gluconeogenesis and blocks glycolysis. These processes make glucose available to the other tissues of the body
The concentration of glucose in human blood plasma is maintained at about 5 mM. The concentration of free glucose inside a myocyte is much lower.
Why is the concentration so low in the cell?
What happens to glucose after entry into the cell?
Glucose is administered intravenously as a food source in certain clinical situations. Given that the transformation of glucose to glucose 6-phosphate consumes ATP, why not administer intravenous glucose 6-phosphate instead?
Glucose enters cells and is immediately exposed to hexokinase, which converts glucose to glucose 6-phosphate using the energy of ATP. This reaction is highly exergonic (ΔG°’ = -16.7 kJ/mol), and formation of glucose 6-phosphate is strongly favoured. Glucose 6-phosphate is negatively charged and cannot diffuse across the membrane. The glucose transporter is specific for glucose; glucose 6-phosphate cannot leave the cell on this transporter and must be
stored (by conversion to glycogen) or metabolized via glycolysis. Intravenous administration of glucose 6-phosphate is not useful because the phosphorylated glucose cannot enter cells on
the glucose transporter or by diffusion
Hormonal Control of Metabolic Fuel
Between your evening meal and breakfast, your blood glucose drops, and your liver becomes a net producer rather than consumer of glucose. Describe the hormonal basis for this switch and explain how the hormonal change triggers glucose production by the liver
The drop in blood glucose triggers release of glucagon by the pancreas. In the liver, glucagon activates glycogen phosphorylase by stimulating its cAMP-dependent phosphorylation and stimulates gluconeogenesis by lowering [fructose 2,6 bisphosphate], thus stimulating FBPase-1, a key enzyme in gluconeogenesis
