bicohem exam 4

Which of the following statements about the urea cycle is TRUE? A. The synthesis of citrulline occurs in the cytoplasm of the hepatocyte. B. One product of the urea cycle is a glycolytic intermediate. C. The two amino groups used to synthesize urea come from aspartate and glutamate. D. It requires four high energy phosphoanhydride bonds to synthesize one molecule of urea.

D. It requires four high energy phosphoanhydride bonds to synthesize one molecule of urea.

Which of the following is NOT a characteristic of acetyl-CoA carboxylase (ACC)? A. The reaction catalyzed by ACC requires ATP and biotin B. The malonyl-CoA product contains one fewer carbon atom than the acetyl-CoA substrate. C. The step catalyzed by ACC is the rate-limiting step in fatty acid biosynthesis. D. ACC is a cytoplasmic enzyme.

C. The step catalyzed by ACC is the rate-limiting step in fatty acid biosynthesis.

Which of the following statements about organ energy use is FALSE? A. Cardiac muscle relies on glucose for its energy needs in both the fed and fasting states. B. The brain consumes approximately 20% of total O2 consumed by a human. C. In most humans, the stores of triacylglycerols in adipose tissue can sustain life for several weeks. D. The liver distributes several types of nutrients to supply other organs with energy. E. During fasting, skeletal muscle degrades protein to provide gluconeogenic substrates to the liver.

A. Cardiac muscle relies on glucose for its energy needs in both the fed and fasting states.

Which of the following processes is NOT seen in an individual with uncontrolled type 1 diabetes? A. Decreased synthesis of ketone bodies. B. Increased hepatic gluconeogenesis. C. Degradation of muscle protein. D. Decreased flux through the citric acid cycle in the liver. E. Increased lipolysis in adipose tissue.

A. Decreased synthesis of ketone bodies.

Where does the glycerol-3-phosphate used in triacylglycerol synthesis in adipose tissue come from? A. pyruvate B. glyceraldehyde-3-phosphate C. glycerol D. glucose

A. pyruvate

What stage of cholesterol synthesis has the enzymatic step that controls the rate at which cholesterol is synthesized? A. Stage 3: the conversion of squalene to cholesterol B. Stage 2: the synthesis of squalene from mevalonate C. Stage 1: the formation of mevalonate

B. Stage 2: the synthesis of squalene from mevalonate

Match the characteristic to its enzyme(s). 1. activated by high levels of AMP 2. inhibited by high levels of AMP 3. activated by high levels of NAD+ 4. serine/threonine kinase 5. deacetylase A. AMPK B. AMPK and mTOR C. mTOR D. sirtuins E. AMPK and sirtuins F. mTOR and sirtuins

1. A 2. C 3. D 4. A 5. D

For each statement, indicate the organ(s) for which the statement is TRUE. (Note: skeletal muscle refers to either resting muscle or muscle under exertion.) 1. The preferred fuel source is fatty acids. 2. Exports molecules that can be used to make glucose. 3. Has glycogen reserves. 4. Has triacylglycerol reserves. 5. Provides fuel to the brain. 6. Does not export fuels to the rest of the organism. A. Skeletal Muscle, Cardiac Muscle, Adipose tissue B. Liver C. Skeletal Muscle, Adipose tissue D. Skeletal Muscle E. Skeletal Muscle, Liver F. Brain G. Adipose tissue, Liver H. Brain, Skeletal Muscle I. Adipose Tissue J. Brain, Cardiac Muscle K. Cardiac Muscle

1. A 2. C 3. E 4. G 5. B 6. J

Match the observed effect in liver to the hormone that was responsible for it. 1. High concentration of cAMP. 2. High concentration of fructose-2,6-bisphophostate. 3. Phosphorylated acetyl-CoA carboxylase I. 4. Increased transcription of glucokinase. 5. Inhibition of carnitine palmitoyltransferase by malonyl-CoA. A. Insulin B. Glucagon

1. B 2. A 3. B 4. A 5. A

Match the lipid metabolic process to its cellular location. 1. beta-oxidation 2. fatty acid synthesis 3. ketone body synthesis 4. cholesterol synthesis 5. triacylglycerol synthesis A. cytoplasm and ER membranes B. cytoplasm C. mitochondrial matrix

1. C 2. B 3. C 4. A 5. A

Refer to the image posted For each enzyme listed below indicate: the pathway it is part of (please use the letters A - H, rather than the pathway name); whether in the LIVER it is activated by the actions of insulin or glucagon. Please use YES or NO in the appropriate box. Enzyme 1. acetyl-CoA carboxylase Insulin: Yes/No Glucagon: Yes/No 2. fructose-1,6-bisphosphatase Insulin: Yes/No Glucagon: Yes/No 3. glycogen phosphorylase Insulin: Yes/No Glucagon: Yes/No 4. glycogen synthase Insulin: Yes/No Glucagon: Yes/No 5. PFK-1 Insulin: Yes/No Glucagon: Yes/No 6. PEP carboxykinase Insulin: Yes/No Glucagon: Yes/No 7. pyruvate kinase Insulin: Yes/No Glucagon: Yes/No 8. pyruvate dehydrogenase (X for pathway) Insulin: Yes/No Glucagon: Yes/No

1. F Insulin: Yes Glucagon: No 2. B Insulin: No Glucagon: Yes 3. D Insulin: No Glucagon: Yes 4. C Insulin: Yes Glucagon: No 5. A Insulin: Yes Glucagon: No 6. B Insulin: No Glucagon: Yes 7. A Insulin: Yes Glucagon: No 8. X Insulin: Yes Glucagon: No

Which of the following statements about diabetes is/are TRUE? 1. Type 1 diabetes is an autoimmune disease, in which the beta cells of the pancreas are destroyed. 2. One hypothesis for the cause of type 2 diabetes is that lipid overload interferes with insulin signaling and blocks the translocation of GLUT4 transporters to the plasma membrane of muscle and adipose cells. 3. 95% of people with diabetes have type 1 diabetes. 4. Currently, the only treatment for type 2 diabetes is insulin injections, whereas type 1 diabetes can be treated with insulin injections or oral medications. 5. One hypothesis for the cause of type 2 diabetes suggests that when adipose cells become larger due to increased TAG content, they secrete inflammatory adipokines and cytokines that interfere with insulin signaling in peripheral tissues. A. 1, 2 and 5 are TRUE B. 2 and 5 are TRUE C. 1 and 2 are TRUE D. 1, 2, 4 and 5 are TRUE E. 2, 3, 4 and 5 are TRUE

A. 1, 2 and 5 are TRUE

For a fatty acid to be used as a substrate in triacylglycerol synthesis it must be: A. Activated to a fatty acyl-CoA by the enzyme acyl-CoA synthetase. B. Phosphorylated at the carboxyl group by the enzyme acyl kinase. C. Transported into the matrix of the mitochondria. D. Have a maximum of 16 carbons.

A. Activated to a fatty acyl-CoA by the enzyme acyl-CoA synthetase. To be used in metabolism, all fatty acids must be activated to an acyl-CoA. This reaction is catalyzed by a family of acyl-CoA synthetase enzymes (choice a). Triacylglycerol synthesis occurs in the cytoplasm, and the acyl chains can vary in length from 16 to 24 carbons

How would one classify an amino acid whose carbon skeleton is degraded to a citric acid cycle intermediate? A. Glucogenic amino acid B. Ketogenic amino acid C. Both glucogenic and ketogenic

A. Glucogenic amino acid Glucogenic amino acids are those that have the carbon skeleton degraded to a molecule that can be used to make glucose. Ketogenic amino acids are those that have the carbon skeleton degraded to a molecule that can be used to make a ketone body - acetyl-CoA or acetoacetyl-CoA. An amino acid whose carbon skeleton is degraded to a citric acid cycle intermediate would be a glucogenic amino acid. Citric acid cycle intermediates would be molecules such as -ketoglutarate, succinyl-CoA, fumarate and oxaloacetate. This definition would NOT include acetyl-CoA, which is the substrate of the citric acid cycle, not an intermediate. Since citric acid cycle intermediates can all be converted to oxaloacetate through the cycle reactions, and since oxaloacetate is an intermediate in gluconeogenesis, then amino acid carbon skeletons that are degraded to CAC intermediates are glucogenic amino acids.

Which of the following statements is FALSE? A. The first step in the synthesis of vitamin D from 7-dehydrocholesterol requires an enzyme. B. Bile salts are formed from bile acids by conjugation reactions with glycine and taurine. C. The synthesis of all steroid hormones starts with the conversion of cholesterol to pregnenolone. D. The synthesis of bile acids is the most important mechanism for degrading and eliminating cholesterol.

A. The first step in the synthesis of vitamin D from 7-dehydrocholesterol requires an enzyme.

Phosphorylation of mTOR can either activate the enzyme or inhibit the enzyme. A. True B. False

A. True

The phosphorylation of mTOR can either activate or inactivate the kinase activity. A. True B. False

A. True The kinease activity of mTOR (mammalian target of rapamycin) is controlled by phosphorylation. The actions of insulin activates PI3 Kinase, which phosphorylates and activates mTOR. However, under nutrient-poor conditions, AMP-activated kinase will phosphorylate and inactivate mTOR. Each of these kinases phosphorylates a different ser/thr residue on mTOR.

Use the figure posted to answer the following questions. Please use the following choices to fill in the blanks. Make sure to watch your spelling :-). fatty acid oxidation, glycolysis, fatty acid synthesis, ketogenesis, glucogenic, ketogenic, gluconeogenesis, ketolysis, glycogenesis, pyruvate carboxylase, glycogenolysis, pyruvate dehydrogenase A. B. C. D. E. F. G. H. What class of amino acid is represented by: J. K. What is the name of the enzyme that catalyzes reaction 1. 2.

A. glycolysis B. gluconeogenesis C. glycogenesis D. glycogenolysis E. fatty acid oxidation F. fatty acid synthesis G. ketogenesis H. ketolysis J. glucogenic K. ketogenic 1. pyruvate dehydrogenase 2. pyruvate carboxylase

Which of the following pathways are turned on through the actions of AMP-activated protein kinase (AMPK)? 1. glycolysis 2. gluconeogenesis 3. fatty acid synthesis 4. cholesterol synthesis 5. lipolysis 6. lipogenesis A. 2, 3, 4 and 6 B. 1 and 5 C. 3 and 4 D. 1 only E. 1, 3 and 6

B. 1 and 5

Acetyl-CoA carboxylase (ACC): A. Is found in the mitochondrial matrix. B. Catalyzes the carboxylation of acetyl-CoA to malonyl-CoA. C. Is inhibited by citrate. D. Is one of the activities in the multifunctional fatty acid synthase enzyme.

B. Catalyzes the carboxylation of acetyl-CoA to malonyl-CoA. ACC is found in the cytoplasm (choice a). It is a separate enzyme from the fatty acid synthase protein (choice d). The acetyl-CoA substrate is moved from the matrix to the cytoplasm as citrate, so citrate activates the enzyme, since it indicates substrate is available (choice c).

Which of the following statements does NOT describe how acetyl-CoA carboxylase (ACC) activity is regulated? A. High levels of cellular AMP will lead to the phosphorylation of the enzyme. B. Citrate binding stimulates polymerization. C. Phosphorylation of the enzyme activates it. D. The active form of ACC is a high-molecular weight polymer.

B. Citrate binding stimulates polymerization.

A major difference between fatty acid synthesis and B-oxidation is: A. NADPH is required for the oxidation of fatty acids but not for their synthesis. B. Synthesis occurs in the cytoplasm while B-oxidation takes place in the mitochondrial matrix. C. Acetyl-CoA, the product of B-oxidation, is not required for fatty acid synthesis. D. Biotin is required for oxidation of fatty acids but not for their synthesis.

B. Synthesis occurs in the cytoplasm while B-oxidation takes place in the mitochondrial matrix. NADPH is the reducing agent in the two oxidation-reduction reactions of fatty acid synthesis. In -oxidation, the oxidizing agents in the two oxidation-reduction reactions are FAD and NAD+ (choice a). Biotin is required for the synthesis of fatty acids, since it is an essential coenzyme of acetyl-CoA carboxylase 1 (choice d). Biotin is not required for oxidation of even-numbered chain fatty acids. It is required for the complete oxidation of odd-chain fatty acids, since the 3-carbon proprionyl-CoA produced in the last round is carboxylated to the 4-carbon methylmalonyl-CoA. Acetyl-CoA is the starting material for the synthesis of palmitate (choice c). It is carboxylated to malonyl-CoA, and used by fatty acid synthase.

In mammals, the urea cycle is the primary mechanism to dispose of excess nitrogen. Which of the following is NOT a characteristic of the urea cycle? A. Urea synthesis begins with the formation of carbamoyl phosphate. B. Synthesis of urea does not require hydrolysis of ATP. C. The reactions in the urea cycle occur in the mitochondrial matrix and the cytoplasm. D. The immediate precursor of urea is arginine.

B. Synthesis of urea does not require hydrolysis of ATP. The first step in the synthesis of urea is the synthesis of carbamoyl phosphate from ammonia, bicarbonate and ATP, in a reaction catalyzed by carbamoyl phosphate synthetase I (choice a). The argininosuccinate is cleaved to arginine and fumarate, and the resulting arginine is cleaved by arginase to urea and ornithine (choice d). The first step of the urea cycle occurs in the matrix of the mitochondria. This step is the condensation of ornithine with carbamoyl phosphate to form citrulline. The remaining steps occur in the cytoplasm (choice c). Synthesis of urea requires 4 high energy phosphoanhydride bonds - 2 to make carbamoyl phosphate and 2 to make argininosuccinate from citrulline and aspartate (choice b).

In humans, fatty acid synthesis occurs on the fatty acid sythase (FAS). Which of the following statements does NOT describe a characteristic of this enzyme. A. The flexibility of the ACP domain means the growing acyl chain can easily move from one active site to another active site on the FAS polypeptide. B. The beta-ketoacyl synthase (KS) domain and ACP domain are located right next to each other on the polypeptide chain. C. Each FAS polypeptide has six catalytic domains plus an ACP domain. D. The FAS enzyme exists as a dimer, which means two fatty acids can be synthesized simultaneously.

B. The beta-ketoacyl synthase (KS) domain and ACP domain are located right next to each other on the polypeptide chain.

Which of the following statements is FALSE? A. The fuel source used by the liver depends on the nutritional state and energy needs of the organism. B. The brain prefers ketone bodies as an energy source, but can use glucose. C. Most of the fatty acids reserved for later energy needs are stored in adipose tissue. D. Active skeletal muscle relies on anaerobic glycolysis to supply its energy needs.

B. The brain prefers ketone bodies as an energy source, but can use glucose. The brain prefers to use glucose as its primary energy source. It can adapt to using ketone bodies as a fuel source, under conditions where glucose is not available (i.e. starvation conditions).

What is the correct order of the reactions catalyzed by fatty acid synthase in the first round of synthesis? 1. The decarboxylation of the malonyl-ACP initiates the condensation reaction that forms beta-ketoacyl-ACP. 2. An acetyl group is transferred from acetyl-ACP to a cysteinyl side chain of KS domain. 3. NADPH provides electrons to reduce the double bond to a single bond. 4. Water is removed, generating a double bond between the alpha and beta carbons. 5. A malonyl group is transferred from malonyl-CoA to the ACP domain. 6. The 4-carbon acyl chain is transferred from the ACP domain to the cysteinyl side chain of the KS domain. 7. An acetyl group is transferred from acetyl-CoA to the ACP domain. 8. NADPH provides electrons to reduce the beta-carbonyl to a beta-alcohol. A. 7 - 2 - 5 - 1 - 6 - 8 - 4 - 3 B. 2 - 7 - 5 - 1 - 3 - 4 - 8 - 6 C. 7 - 2 - 5 - 1 - 8 - 4 - 3 - 6 D. 2 - 5 - 1 - 8 - 4 - 3 - 6 - 7

C. 7 - 2 - 5 - 1 - 8 - 4 - 3 - 6

Which of the following statements about the regulation of fatty acid metabolism is TRUE? A. High concentrations of malonyl-CoA inhibit both carnitine palmitoyltransferase I and acetyl-CoA carboxylase. B. After an overnight fast, carnitine palmitoyltransferase I activity is inhibited by malonyl-CoA. C. Directly after a meal, acetyl-CoA carboxylase will exist as a polymer. D. Fatty acid metabolism is only regulated by allosteric mechanisms.

C. Directly after a meal, acetyl-CoA carboxylase will exist as a polymer. Directly after a meal, insulin is being secreted due to high levels of glucose in the blood stream. Insulin acts to turn on pathways that store fuel for later needs. Therefore, fatty acid synthesis will be turned on. This is done by activating acetyl-CoA carboxylase, the rate-limiting step of fatty acid synthesis (choice c). Insulin acts to remove phosphate from the protein, which allows the enzyme to form an active polymer. Malonyl-CoA is an allosteric inhibitor of carnitine palmitoyltransferase I, but it has no allosteric effects on acetyl-CoA carboxylase (choice a). After an overnight fast, glucagon is being secreted because the body needs energy. Fatty acid synthesis will be turned off (acetyl-CoA carboxylase will exist as a phosphorylated, inactive dimer), so malonyl-CoA will not be made. Therefore, without the presence of the inhibitor, acyl chains will be transferred from CoA to carnitine by CPTI (choice b), in order to move the acyl chain into the matrix for B-oxidation. Fatty acid metabolism is regulated by allosteric mechanisms and covalent modification (choice d).

Metformin is a type-2 diabetes drug that reduces hepatic gluconeogenesis, leading to reduced glucose concentrations in the blood. Studies show metformin inhibits complex I of the mitochondrial electron transport chain. Which of the following statements does NOT help to explain how metformin acts to inhibit gluconeogenesis? A. Gluconeogenesis requires the hydrolysis of six high-energy phosphoanhydride bonds. B. AMP is an allosteric inhibitor of fructose-1,6-bisphosphatase. C. Inhibition of complex I completely shuts down the synthesis of ATP through oxidative phosphorylation. D. No NADH electrons will flow through the electron transport chain if complex I is inhibited.

C. Inhibition of complex I completely shuts down the synthesis of ATP through oxidative phosphorylation.

Which of the following statements about sirtuins and their protein targets is FALSE? A. Mammals possess seven sirtuins that differ in cellular localization. B. In most cases, SIRT-mediated deacetylation of a target protein increases the activity of the target protein. C. The activity of sirtuins is enhanced at when there are higher levels of NADH than NAD+ inside the cell. D. Sirtuins act on many proteins besides histones.

C. The activity of sirtuins is enhanced at when there are higher levels of NADH than NAD+ inside the cell.

Why might someone say that alanine, serine, threonine, cysteine and glycine are ketogenic amino acids? (Hint: it would be useful to look at Fig. 18.12 to answer this question.) A. The carbon skeletons are degraded to acetoacetyl-CoA. B. The carbon skeletons are degraded to two products: acetyl-CoA and a citric acid cycle intermediate. C. The carbon skeletons are degraded to pyruvate, which can be converted to acetyl-CoA by the pyruvate dehydrogenase complex.

C. The carbon skeletons are degraded to pyruvate, which can be converted to acetyl-CoA by the pyruvate dehydrogenase complex.

The carbon atoms in the cholesterol molecule come from: A. Acetyl-CoA and aspartate B. Succinyl-CoA C. Acetyl-CoA and malonyl-CoA D. Acetyl-CoA

D. Acetyl-CoA

Which of the following statements about the HMG-CoA reductase reaction is FALSE? A. Two molecules of NADPH are required. B. A carboxyl group is reduced to a hydroxyl group. C. Phosphorylation of the enzyme diminishes its catalytic activity. D. The reaction occurs within the ER lumen.

D. The reaction occurs within the ER lumen.

How many acetyl-CoA molecules are required to synthesize the ketone body, β-hydroxybutyrate? A. Four B. Two C. One D. Three

D. Three

You may want to refer to Figure 18.12 to answer this question. The degradation of which amino acid generates a product formed in the last step of odd-chain fatty acid oxidation? A. serine B. proline C. asparagine D. methionine

D. methionine

Which of the reaction(s) below is/are a transamination reaction? (1) serine + tetrahydrofolate --> glycine + N5,N10-methylene tetrahydrofolate (2) a-ketoglutarate + NH4+ + NADH + H+ --> glutamate + NAD+ + H2O (3) alanine + a-ketoglutarate --> pyruvate + glutamate A. Reactions 1 and 3 B. Reactions 2 and 3 C. Reaction 1 D. Reaction 2 E. Reaction 3

E. Reaction 3 A transamination reaction transfers amino groups between a-keto acids and amino acids, so the reaction will have 2 amino acid/a-keto acid pairs as reactants. Only reaction 3 is a transamination reaction. The amino acid/a-keto acid pairs are: alanine/pyruvate and glutmate/a-ketoglutarate. Reaction 1 uses a 1-carbon carrier, tetrahydrofolate, which accepts the methoxyl group from serine to form glycine. Reaction 2, catalyzed by glutamate dehydrogenase, is one way free ammonia (NH4+) can be incorporated into a biological molecule

The synthesis of urea only occurs in the liver. Since high levels of ammonia are toxic, how does the body get amino groups from extrahepatic tissues to the liver? A. as alanine, glutamine and glutamate B. as glutamine only C. the deamination of amino acids only occurs in the liver D. as alanine only E. as alanine and glutamine F. as glutamate only

E. as alanine and glutamine