MCB 450 Exam 4

High levels of ATP and citrate:

Inhibit glycolysis
Indicate remote gluconeogenesis
Indicate a high energy-well fed state.

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

High NADH

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, and pantothenic acid

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

α-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.

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 principle electron donor to the O2, the last electron acceptor in the electron-transport system.

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

Dehydration followed by hydration

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

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

Substrate channeling

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

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

Decarboxylation, oxidation, transfer to CoA

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

10

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.

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.

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 one third of the carbons of newly synthesized malonyl CoA.

The β-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 hormones 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.

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

Condensation: Step 1
Reduction: Step 2
Dehydration: Step 3
Reduction: Step 4

A 20-year-old woman with diabetes mellitus was admitted to the hospital in a semi-conscious 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 increased clearance of ethanol from the blood.

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

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

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.

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 acetaldehyde to acetate, which causes reduced clearance of acetaldehyde.

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

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.

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?

Liver cirrhosis

The synthesis of glucose fro pyruvate by gluconeogensis:

requires the participation of biotin

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 is most likely to occur in a normal individual after ingesting a high carbohydrate meal?

Only insulin levels increase

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 36-year old man with viral pneumonia has an episode of hemolysis. Over the next week, he has an increased rate of reticulocytosis. Which of the following compounds serves as a precursor to heme in reticulocytes?

Succinyl-CoA

Coenzyme A is an acyl group carrier. The acyl group is linked to coenzyme A via the:

Thioester bond

A 50-year-old chronic alcoholic presents with dementia, paralysis of lateral gaze, and difficulty walking. The vitamin deficient in this patient is required as a cofactor for which of the following?

Pyruvate dehydrogenase

In the citric acid cycle, succinate thiokinase (succinyl CoA synthetase) catalyzes the cleavage of the succinyl-CoA thioester bond with formation of a high-energy compound. This compound can then be used by the body in which of the following biochemical pathways?

Elongation of the polypeptide chain

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

The target of statins is:

HMG CoA reductase

Which lipoprotein particle functions in "reverse" cholesterol transport?

HDL

Which lipoprotein particle delivers dietary cholesterol to the liver?

Chylomicrons

Which lipoprotein particle is secreted by the liver pre-loaded with lipids?

VLDL

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

Pancreatic lipase

Which of these enzymes is responsible for releasing fatty acids from stored triacylglycerols in adipocytes?

Hormone sensitive lipase

Which of these enzymes is responsible for releasing fatty acids from circulating chylomicrons?

Lipoprotein lipase

Which of these statements about chylomicrons is true?

Chylomicron levels would be lowest following an overnight fast

Which of these cell types are unable to oxidize fatty acids via beta oxidation?

Red blood cells

A teenager, concerned about his weight, attempts to maintain a fat-free diet for a period of several weeks. If his ability to synthesize various lipids were examined, he would be found to be most deficient in his ability to synthesize:

Prostaglandins

Long-chain fatty acids are shuttled into the mitochondrion bound to what molecule?

Carnitine

A 7-year-old girl is brought to the emergency department by her parents with a complaint of severe polyuria. Laboratory examination reveals ketones in her urine. Which of the following is the most likely source of the ketones?

Free fatty acid breakdown

A 30-year-old man has been fasting for religious reasons for several days. His blood glucose level is now about 60% of its normal value, but he does not feel lightheaded because his brain has reduced its need for serum glucose by using which of the following substances as an alternate energy source?

Beta-hydroxybutyrate

A 57-year-old man with type 1 diabetes mellitus has progressive retinopathy. Ophthalmoscopic examination reveals macular edema and retinal thickening with hard exudates of yellow-white lipid deposits. Which of the following contributes to hyperlipidemia in type 1 diabetes, and thus the risk for lipid deposition in the retina?

Overactive hormone-sensitive lipase

The oxidation of fatty acids is best described by which of the following sets of reactions?

Oxidation, hydration, oxidation, carbon-carbon bond breaking

In which one of the following periods will fatty acids be the major source of fuel for the tissues of the body?

While running the last mile of a marathon