MCB 450 Exam 4 (Homeworks + Extra Stuff)

What are the steps involved (in order) in the conversion of pyruvate to acetyl CoA?

Decarboxylation, oxidation, transfer to CoA.

A mutation in the active site of succinyl CoA synthetase where His is converted to Lys would result in which of the following?

Loss of a succinyl phosphate intermediate.

Although we study the citric acid cycle as the final stage oxidation of carbon from glucose, an in-depth look at the cycle shows intermediates entering and leaving the cycle from a number of metabolic pathways. With all of these demands on the cycle, how does it maintain a minimal level of oxaloacetate (OAA) to allow the cycle to function?

OAA is synthesized via pyruvate carboxylase in an anaplerotic reaction that occurs when acetyl CoA is present

The citric acid cycle is activated in the presence of oxygen (O2), but what is the link between the citric acid cycle and O2?

A primary product of the citric acid cycle is NADH, the principal electron donor to the O2, the last electron acceptor in the electron-transport system.

Which of the following conditions will activate pyruvate dehydrogenase kinase, which catalyzes the phosphorylation and inactivation of E1 in the pyruvate dehydrogenase complex?

Elevated concentrations of NADH and ATP

In gluconeogenesis aldolase functions to convert one Glyceraldehyde 3-phosphate and one dihydroxyacetone phosphate to the following product(s)?

Fructose 1,6-bisphosphate

Glycolysis and gluconeogenesis are reciprocally regulated by a common regulator, fructose-2,6- bisphosphate. Levels of fructose-2,6-bisphosphate are regulated by:

the bifunctional enzyme PFK-2 and FBPase-2 which is encoded in a single protein.

What is the effect of Protein kinase A phosphorylation of the dual function enzyme PFK-2/FBPase-2?

Inhibits PFK-2 kinase activity.

Why is it important that Biotin be linked to a flexible arm of pyruvate carboxylase?

The biotin needs to move between the separated biotin carboxylation and carboxyltransferase sites between adjacent copies of the protein in a tetramer.

During vigorous exercise, stimulation of the tricarboxylic acid (TCA) cycle results principally from:

stimulation of the flux through a number of TCA cycle enzymes by a decreased NADH/NAD+ ratio.

The beta-oxidation of myristyl-CoA (14:0) yields:

7 acetyl CoA + 6 FADH2 + 6 NADH + 6 H+

Fatty acid synthesis is regulated by hormone depending on feeding vs. fasting and recent exercise vs. no recent exercise. Which hormone(s) is/are active and what is their mechanism of action of the(se) hormone(s) after exercise and a meal?

Insulin stimulates fatty acid synthesis by activating acetyl CoA carboxylase 1.

What are the conditions that lead to a "beer gut" due to the excess consumption of alcohol?

Excess ethanol metabolism leads to an accumulation of NADH that inhibits fatty acid metabolism.

Considering the final steps in cholesterol biosynthesis, when squalene is eventually converted to lanosterol, which of the following statements is correct?

Squalene monooxygenase is considered a mixed function oxidase because it catalyzes a reaction in which only one of the oxygen atoms of O2 is incorporated into the organic substrate.

Why do lipoprotein particles (e.g., VLDL) only have a monlayer of phospholipids instead of a typical lipid bilayer?

The acyl chains of the phospholipid monolayer interact with the triglycerides and cholesterol esters of the particle.

Humans can convert cholesterol to each of the following, EXCEPT:

CO2 + H2O

Lovastatin is used to lower cholesterol by inhibiting the function of which protein?

HMG-CoA reductase.

Suppose 14C-labeled CO2 is used to form malonyl-CoA from acetyl-CoA. If this labeled malonyl-CoA is used for palmitate synthesis, which carbon atom(s) in the fatty acid would be radiolabeled?

None of the carbons

Fatty acids are adenylated prior to reacting with Coenzyme A to make Acyl-CoA. What is the purpose of the adenylation?

This creates a phospho-ester bond that can be "attacked" by Coenzyme A.

When fatty acid biosynthesis is stimulated, β-oxidation of fatty acids is inhibited. This inhibition occurs mainly because:

Malonyl-CoA inhibits carnitine acyltransferase I

Odd chain fatty acids and some amino acids produce propionyl CoA. Which of the following is NOT required for the metabolism of propionyl CoA to succinylcholine CoA?

NADH

Triacylglycerol synthesis in adipose tissue occurs only in the fed state. Why?

Adipose tissue lacks glycerol to make glycerol-3-phosphate from glycerol. Therefore, glycerol-3-phosphate can only be obtained from the glycolytic pathway (fed state), and the reduction of dihydroxyacteone phosphate (DHAP)

The carnitine derivatives of fatty acids are utilized for

Shuttling fatty acids across the mitochondrial membrane

Which of the following compounds is a potent stimulator of palmitate synthesis, an allosteric activator of acetyl-CoA carboxylase, and a source of both cytoplasmic acetyl-CoA and NADPH for lipogenesis

Citrate

Which of the following is responsible for down regulation of fatty acid synthesis under low energy conditions?

AMP activation of AMP activated protein kinase (AMPK)

Which of the following statements about chylomicrons is incorrect?

The main role of chylomicrons is to deliver cholesterol to the tissues and fatty acids to the liver

Prior to removal of an acetyl-CoA in beta-oxidation, the saturated beta carbon must be

Oxidized, hydrated, and oxidized again to form 3-ketoacyl CoA

Which of the following is NOT true about fatty acid synthesis?

Fatty acid synthesis occurs in the mitochondria

What is the role of biotin in beta oxidation of ODD chain carbon fatty acids

Biotin takes part in the addition of a CO2 to propionyl-CoA

Coenzyme A and acyl carrier protein (ACP) resemble one another since both

Contain 4'-phosphopantetheine

Beta-oxidation of fatty acids with even number of carbons will produce all of the following except:

Malony-CoA

The end product of glycolysis is pyruvate. However, pyruvate cannot directly enter the TCA cycle. What needs to happen to pyruvate for the TCA cycle to proceed?

Pyruvate must lose a CO2 when it reacts with TPP and form hydroxyethyl-TPP, the acetyl group linked to TPP must be transferred to lipoamide and CoA-SH aquires an acetyl group to make acetyl-CoA

What is TRUE about the reciprocal regulation of glycolysis and gluconeogenesis?

ADP inhibits pyruvate carboxylase and activates pyruvate kinase, ATP inhibits phosphofructokinase and ATP activates fructose 1,6 bisphosphatase

What is the effect of protein kinase A phosphorylation of fructose 2,6-bisphosphate?

Inhibits fructose 2,6- bisphosphatase kinase domain

What is the role of adenylate cyclase in gluconeogenesis?

Converts ATP to cAMP, which activates PKA

How does arsenite poisoning take effect?

Arsenite covalently attached to dihydrolipoamide and prevents pyruvate processing to acetyl-CoA

Which of the following coenzymes are used by alpha ketoglutarate dehydrogenase complex?

All of the above: Lipoic acid, CoA, Thiamine, FAD & NAD+

During cholesterol synthesis how is C-30 squalene made?

Successive condensation of six 5 carbon isoprene molecules

Bile salts are amphipathic. How does this help emulsify dietary fats?

The hydroxyls and carboxylate of bile salts face the aqueous environment while the hydrophobic methyl groups interact with insoluble fats

How can excess bile acids be reduced?

Increase dietary fiber in diet and taking cholestyramine

What is true about omega fatty acids?

The omega number is independent of the length of the fatty acid and the omega number (e.g. Omega-3) indicates where the first double bond is relative to the final carbon in the fatty acid

Alcohol abuse is a frequent cause of liver disease in the USA. In recent years, many attempts have been made to help alcoholics stop drinking. Disulfiram is one of the potential pharmacological approaches for preventing alcoholics from drinking. What is the name of the enzyme that is targeted by disulfiram?

Acetaldehyde dehydrogenase

Chronic alcohol results in induction of Cytochrome P450 2E1 (CYP2E1) enzyme in the liver. Although the induction is a compensatory mechanism to metabolize excess alcohol, it can have negative consequences BECAUSE it

Leads to faster acetaldehyde production that can be cleared

Tangier disease is characterized by a severe plasma deficiency or absences of HDL by accumulation of cholesterol esters in many tissues throughout the body. Which of the following proteins or enzymes is deficient in this condition?

ABCA1 (ATP binding cassette protein 1)

The fate of acetate, the product of ethanol metabolism is which of the following?

It is taken up by other tissues and activated to acetyl CoA

The synthesis of glucose from pyruvate by gluconeogenesis:

Requires the participation of biotin

In the non-oxidative stage of the Pentose-PO4 pathway, intermediates of _____________ are produced.

Glycolysis

Which one of the following is a common intermediate in the conversion of glycerol and lactate to glucose?

Glucose 6-phosphate

Which one of the following reactions is unique to gluconeogenesis?

Oxaloacetate to phosphoenolpyruvate

Which of the following would be expected to occur after acute alcohol ingestion?

Lactic acidosis

A 34-year-old woman presents to her physician complaining of oral ulcers. A careful history reveals that she is a strict vegetarian and does not eat meat, fish, poultry, eggs, or dairy products. She is found to have a severe riboflavin deficiency. The function of which enzymes in the TCA cycle would be most directly affected by the riboflavin deficiency?

Succinate dehydrogenase

Mammalian pyruvate dehydrogenase complex (PDC) is inactivated by pyruvate dehydrogenase kinase in the presence of:

High NADH

Which lipoprotein particle functions in "reverse" cholesterol transport?

HDL

Which of these enzymes is primarily responsible for digesting dietary triacylglycerols in the small intestine?

Pancreatic lipase

High levels of ATP and citrate:

All of the above: Indicate a high energy-well fed state, inhibit glycolysis, & indicate remote gluconeogenesis

Which of the following would be associated with LOW pyruvate dehydrogenase rate?

Low NAD+

The hallmarks of acute alcoholism without food intake are acidosis and hypoglycemia. These metabolic changes are due to the:

Metabolism of ethanol, which prevents the production of sufficient levels of blood glucose from lactate, glycerol and alanine

Hormonal activation of cyclic AMP levels will:

Increase the activation of gluconeogenesis

Which of the following vitamins are precursors to coenzymes that are necessary for the formation of acetyl CoA from pyruvate?

Thiamine, riboflavin, niacin, lipoic acid, pantothenic acid, and biotin

In addition to pyruvate dehydrogenase, what other enzyme(s) in the citric acid cycle has a key thiamine pyrophosphate coenzyme?

a-ketoglutarate dehydrogenase

Why does acetyl CoA, a product of fatty acid catabolism, influence the pyruvate dehydrogenase complex (PDH), a control point in carbohydrate catabolism?

When fatty acid breakdown is high, PDH is inhibited by acetyl CoA due to pyruvate kinase activity

What is/are the chemical change(s) involved in the conversion of citrate into isocitrate?

Dehydration followed by hydration

The direct movement of substrates from one enzyme to the next is called:

Substrate channeling

Approximately how many ATP or GTP equivalents are produced during one turn of the citric acid cycle?

10

A 1-month-old male showed abnormalities of the nervous system and lactic acidosis. Enzyme assay for pyruvate dehydrogenase (PDH) activity on extracts of cultured skin fibroblasts showed 5% of normal activity, with a low concentration (1 x 10-4 mM) of thiamine pyrophosphate (TPP), but 80% of normal activity when the assay contained a high (0.4 mM) concentration of TPP. Which one of the following statements concerning this patient is most correct?

Administration of thiamine is expected to reduce his serum lactate concentration and improve his clinical symptoms

The following is the sum of three steps in the citric acid cycle. A + B + FAD + H2O → C + FADH2 + NADH Choose the lettered answer that corresponds to the missing "A", "B", and "C" in the equation. Reactant A Reactant B Reactant C

Succinate NAD+ oxaloacetate

Which of these compounds is oxidized by a multienzyme complex that requires five different coenzymes?

Pyruvate

A low level of carbon dioxide labeled with 14C is accidentally released into the atmosphere surrounding industrial workers as they resume work following the lunch hour. Unknowingly, they breathe the contaminated air for 1 hour. Which of the following compounds will be radioactively labeled?

About 1/3 of the carbons of newly synthesized malonyl CoA

What are the repeated steps of β-oxidation? List the number associated with each step in chronological order (beginning to end). Assume saturated fatty acyl chain and even number of carbons.

Oxidation, hydration, oxidation, thiolysis

What is the role of carnitine acyltransferase-I?

Reacts with Acyl-CoA and L-carnitine to transfer the acyl chain to make Acyl-carnitine

A 20-year-old woman with diabetes mellitus was admitted to the hospital in a semiconscious condition with fever, nausea and vomiting. The woman's breath smelled of acetone. A urine sample was strongly positive for ketone bodies. In this patient:

An insulin injection would alleviate her ketoacidosis by decreasing ketone body production

Increased expression of the enzyme cytochrome P450 2E1 in chronic alcoholics would result in which of the following?

An increase of one's alcohol tolerance level

A person has entered a hunger strike. After five days of starvation, what kind of fuel is being utilized?

Protein from skeletal muscle and fat from adipose tissue

A person has entered a hunger strike. After 60 days of starvation, this person is on the edge of dying. What is likely to be the cause of death?

The breakdown of essential proteins of the brain and heart

A chronic alcoholic is in treatment for alcohol abuse. The drug disulfiram is prescribed for the patient. This drug deters the consumption of alcohol by which of the following mechanisms?

Inhibiting the conversion of acetylaldehyde to acetate, which causes reduced clearance of acetylaldehyde

A young girl with a history of severe abdominal pain was taken to her local hospital at 5 a.m. in severe distress. Blood was drawn, and the plasma appeared milky, with the triacylglycerol level in excess of 2,000 mg/dl (normal = 4-150 mg/dl). The patient was placed on a diet severely limited in fat, but supplemented with medium-chain fatty acids.

Which of the following lipoprotein particles are most likely responsible for the appearance of the patient's plasma?

Chylomicrons

Medium-chain fatty acids are given because they:

Enter directly into the portal blood, and can be metabolized by the liver

Which one of the following consequences of chronic alcohol consumption is irreversible?

Wernicke-Korsakoff syndrome

Most of the enzymes are made of

Amino acids

Lipid functions include all of the following except

Forming the skeletal muslce fibers

TRUE or FALSE: Adenosine monophosphate will have an inhibiting effect on PFK.

False

Which of the following enzymatic steps are not part of the gluconeogenesis pathway?

Hexokinase

TRUE or FALSE: Adenosine monophosphate (AMP) will have an inhibitory effect on fructose 1,6-bisphosphatase.

True

TRUE or FALSE: Insulin stimulates gluconeogenesis.

False

TRUE or FALSE: High blood sugar after a meal increases the level of insulin released by the pancreas.

True

TRUE or FALSE: PDH phosphatase deficiency results in high levels of acetyl CoA.

False

TRUE or FALSE: The order of the steps involved in the conversion of pyruvate to acetyl CoA is: decarboxylation, oxidation, transfer to CoA.

True

TRUE or FALSE: The conversion of malate to oxaloacetate generates one molecule of FADH_2.

False

Which of these compounds is oxidized by a multienzyme complex that requires five different coenzymes?

Alpha-ketoglutarate.

TRUE or FALSE: Elevated concentrations of NADH and ATP will activate PDH kinase.

True

Bile salts are amphipathic. How does this help emulsify dietary fats?

The hydroxyls and carboxylate of bile salts face the aqueous environment while the hydrophobic methyl groups interact with insoluble fats.

Why do lipoprotein particles (e.g. VLDL) only have a monlayer of phospholipids instead of a typical lipid bilayer?

The acyl chains of the phospholipid monolayer interact with the triglycerides and cholesterol esters of the particle.