Biochem unit 3/4 Tests

What is ApoB48 & ApoB100 markers for?

ApoB48 = chylomicrons ApoB100 = VLDL

Which enzyme is the regulatory step in the urea cycle?

CPS1 - carbamoyl phosphate syntehtase

Which of the following is the regulated step of lipogenesis in eukaryotes?

Carboxylation of acetyl-CoA

Which of the following compounds is not synthesized from cholesterol?

Guanine

Infant becomes lethargic after several feedings. Unusual urine smell. abnormal AA in screening. BCAA are elevated. Elevation of which one of the following AA would be consistent with the report?

Isoleucine Maple Syrup Disease

Under cellular conditions when cholesterol is low, which of the following is a true statement regarding the sterol response element binding protein?

It will be associated with the sterol response element (SRE) in the DNA

Homocustinuria can be caused by several different enzyme or vitamin deficiencies. An elevation of homocystine and a decrease in cysteine would most likely present due to which of the following deficiencies?

Loss of function of cystathionine-β synthase (homocystine -> cysteine)

S-adenosylmethionine (SAM) is synthesized from ATP and methionine. A deficiency in which of the following enzymes would impair the production of SAM?

MAT - Methionine adenosyltransferase Methionine adenosyltransferase (MAT) is the enzyme required for the metabolism of methionine to SAM.

What is malic enzyme responsible for?

Malic enzyme is responsible for the conversion of malate to pyruvate and generation of NADPH.

Methotrexate is a potent anticancer agent that starves dividing cells of deoxyribonucleotides through DIRECT inhibition of which of the following processes.

Metabolism of folic acid Methotrexate is an inhibitor of dihydrofolate reductase

Which of the following AA is essential?

Methionine

The LDL receptor is also highly regulated in the cell. Which of the following proteins targets the LDL receptor for degradation?

Proprotein convertase subtilisin/kexin type 9 (PSK9)

Under conditions when glucose oxidation is elevated, the acetyl-CoA produced will allosterically activate which of the following enzymes leading to an increase in the production of oxaloacetate?

Pyruvate carboxylase will synthesize oxaloacetate in the mitoch. to produce citrate.

Which of the following compounds/substrates is required for the synthesis of tyrosine?

Req: Phenlananine, BH4 Not Req: THF, Tryptophan

What do statins do?

Stains inhibit HMG-CoA reductase and reduce de novo synthesis of cholesterol.

The reaction of ammonia with α-ketoglutarate is catalyzed by _________ and requires _________ as a reactant.

The reaction of ammonia with α-ketoglutarate is catalyzed by GDH (glutamate dehydrogenase) and requires NADH or NADPH as a reactant. * reversible step of glutamate synthesis

Bile salts are synthesized from cholesterol and are used for the emulsification of dietary lipids. What is the primary fate of bile salts during digestion?

They are reabsorbed in the ileum

The ribonucleotide reductase is important for converting ribose bases to the deoxy form. This conversion is coupled with the oxidation of the following compounds?

Thioredoxin The reaction is coupled with thioredoxin reductase, reduced thioredoxin and the reductase. In the reaction, thioredoxin is oxidized. This compound is re-reduced by NAPDH so it can be regenerated as part of the reaction

Which enzyme is used DIRECTLY in the synthesis of dTMP?

Thymidylate synthase

You are being chased by a bear. Under these conditions levels of epinephrine are increased due to metabolism of which of the following AA?

Tyrosine tyrosine is metabolized to epinepherine and norepinepherine in neural cells

Which of the following characteristics distinguish most RNA molecules from DNA?

Uridine base on RNA, whereas a thymidine base on DNA

VLDL particles have which of the following combinations of apoproteins in their mature form?

VLDL particles are characteristic of ApoB100, ApoCII, ApoE.

What do the following pathways require: 1. Metabolism of homocysteine to cysteine 2. Metabolism of phenylalanine to tyrosine 3. Conversion of methyl malonyl-CoA to succinyl-CoA

1. Metabolism of homocysteine to cysteine B6 2. Metabolism of phenylalanine to tyrosine BH4 3. methyl malonyl-CoA to succinyl-CoA B12

What is the difference between ACAT and LCAT?

ACAT is primarily responsible for trapping cholesterol in the cell whereas LCAT is found in circulation associated with HDL.

Glucogenic AA that are used in the process of gluconeodenesis and will be metabolised to all of the following compounds except:

Acetyl-COA

Which of the following is the regulatory enzyme for fatty acid synthesis?

Acetyl-CoA carboxylase ( synthesis of malonyl-Coa) Rxn requires: CO2 Biotin

An increase in the ratio of insulin to glucagon leads to which of the following metabolic shifts?

Acetyl-CoA carboxylase will become dephosphorylated and active Fed state pathways will activate acetyl-Coa Carboxylase through dephosphorylation

Fatty acid synthase is a multimeric enzyme complex. Which of the following subunits contains pantothenic acid as a cofactor?

Acyl carrier protein (ACP)

Glucose-alanine cycle is a method of transferring ammonia from the skeletal muscle to the liver. In this process the non-toxic carrier of ammonia is which of the following?

Alanine its shuttled from the skeletal muscle to the liver where it is deaminated to create pyruvate. Pyruvate -> glucose -> back to muscle

A 12-year-old male is brought to his primary care physician. His parents are concerned with his recent decline in school work due to persistent blurred vision. On physical exam, planar xanthomas are noted and laboratory testing reveals extremely low plasma HDL. This presentation would be consistent with a loss of which of the following apoproteins?

Apo A

The interaction of chylomicrons with lipoprotein lipase is stimulated by which of the following Apo proteins?

ApoC II acquired from an interaction with HDL and is required to activate the lipoprotein lipase.

N-acetylglutamate (NAGs)

CSP1 (regulatory enzyme for the urea cycle)

Folate is an essential compound in the synthesis of nucleotides. All of the following nucleotides require folate for sythesis except:

CTP Folate contributes carbons to all the listed bases with the exception of CTP

Which of the following is not required for the transport of newly synthesized fatty acids to the adipose?

Carnitine to shuttle the fatty acids out of the mitochondria This is required for B-oxidation to transport fatty acyl chains into the mitochondria.

In the reaction catalyzed by cholesteryl ester transfer protein (CETP), the VLDL particle receives which of the following compounds from HDL particles?

Cholesteryl-ester

Shortly after meal high in fat, you would expect an elevation of which of the follow lipoproteins in circulation?

Chylomicrons carry dietary fats and cholesterol, therefore after a high fat meal these would be elevated in circulation.

A 17 year old girl dis diagnosed with Vit B12 (cobalimin) deficiency. What reaction is now compromised?

Cobalamin is required for the conversion of methyl malonyl-Co A to succinylCoA

pyridoxal phosphate (PLP)

Cofactor required for all transamination reactions. Including transamination of amino acids.

In the salvage of purines, hypoxanthine-guanine phosphoribosyl transferase (HGPRT) is responsible for which of the following processes?

Conversion of guanine to guanosine monophosphate (GMP) Important enzyme for purine recycling.

A 55 year old man is diagnosed with hyperhomocusterinemia, due to a defieicy in cystathionin-B synthase. Which one of the following amino acids would become essential?

Cysteine

Insulin stimulates lipogenesis through several mechanisms. Which of the following is not an insulin stimulated process that enhances lipogenesis?

Decreased activity of the pyruvate dehydrogenase complex Insulin will stimulate = PDC, Acetyl CoA carboxylase, & glucose transport into cells.

A 47-year-old male is prescribed a statin (HMG-CoA reductase inhibitor) to manage his elevated LDL cholesterol. What is the initial mechanism of action for obtaining the desired effect in this man?

Decreasing hepatic cholesterol biosynthesis Statins inhibit HMG-CoA reductase

Infant brought to the ER with extremely high plasma ammonia, high urine orotic acid and uricil. A defect in which of the following enzymes is the most likely diagnosis.

Error in the Urea cycle since high orotic acid AND high ammonia. Ornithin transcabomalyse deficiency would cause these symptoms. Since there would be an increase in carbamoyl phosphate.

What is the purpose of cholesterol esterification within the cell? (The conversion of cholesterol to cholesteryl ester)

Esterification traps cholesterol in the cell

ATP can be generated by many metabolic pathways in the body. Which of the following processes generates the most ATP?

Fatty acid β-oxidation 7NADH, 7FADH2, 8 acetyl-coa

How does glucagon effect lipolysis?

Glucagon will increase levels of lipolysis through the phosphorylation & activation of hormone sensitive lipase.

A women refuses food for 2 weeks. Under these conditions there is an increased reliance on which of the following pathways for fuel?

Gluconeogenesis Starvation leads the brain to oxidize ketones as a primary fuel source, lowering the reliance on glucose.

What interaction takes place between HDL and VLDL?

HDL particles interact with VLDL particles to exchange cholesteryl ester for triacyclglycerols.

Under fasting conditions (ratio of insulin to glucagon <1), elevated glucagon will activate which of the following enzymes?

Hormone sensitive lipase.

Which of the following best describes the mechanism of action of statins and describes why this drug is an effective therapy for individuals with hypercholesterolemia?

Inhibit 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase, a key regulator of cholesterol synthesis.

In liver, which of the following key inhibitory events ensures that newly synthesized palmitoyl-CoA is not immediately oxidized?

Inhibition of carnitine-palmitoyl transferase-I (CPT-I) by malonyl-CoA.

Which of the following is the common intermediate for purine synthesis

Inosine monophosphate (IMP)

An 11-year-old girl is brought to the emergency department by her father. He reports she has recently been very thirsty and needing to make frequent trips to the bathroom. A rapid dipstick test revealed glucose in her urine and further diagnostics were consistent with a diagnosis of type 1 diabetes. Evaluation of this girl's liver would reveal an increased rate of which of the following processes?

Ketogenesis Fasted state pathways would be high leading to hyperglycemia & ketogenesis

A 45-year-old man is found to have an elevated serum cholesterol of 300mg/dL after a 12 hr. fast. Which of the following lipoproteins would be the largest contributors to a measurement of plasma cholesterol in a normal person following a 12 hr. fast?

LDL & HDL are the major carriers of cholesterol in circulation. VLDLs would be the best represented of serum triglycerides

In reverse cholesterol transport, HDL interacts with the ABC transporters to move cholesterol from the cell to the HDL. This also requires the activity of which of the following enzymes?

Lecithin cholesterol acyltranferase (LCAT)

In the fasted state, fatty acyl-CoAs are transported across the mitochondrial membrane. The transport of fatty acids via carnitine palmitoyl transferase I (CPTI) can be directly inhibited by which of the following compounds?

Malonyl-CoA

What insures that fatty acid synthesis and B-oxidation are not occurring at the same time?

Malonyl-Coa is produced in the cytosol during fatty acid synthesis. This will inhibit transport of fatty acids across the Mitoch membrane.

Malate can be converted to pyruvate in the cytosol. Which of the following compounds is directly generated in this conversion and is essential for fatty acid synthesis?

NADPH producing cytosolic NADPH is essential for FA synthesis, since it is a reducing agent.

PSK9

PSK9 is a regulator of LDL receptor recycling. It targets the receptors for degradation rather than allowing them to be recycled to the cell surface.

During the fasted state, lipolysis is facilitated by the action of hormone sensitive lipase. This enzyme requires which of the following modifications for activation?

Phosphorylation.

Which of the following is the primary role of glutaminase in the liver?

To free an amine group from glutamine. (Glutamine -> Glutamate + NH4) In the fasted state, glutamine will be in excess due to protein catabolism, in Fed state AA will come from dietary intake.

Theregulation of PRPP synthetase is critical in the production of both purines and pyrimidines. This enzyme is inhibited under which of the following conditions?

When both GDP and ADP are elevated

The conversion of ribose bases into deoxy-bases will be occurring under which of the following conditions?

When cells are proliferating Will only occur when they are needed for the process of DNA synthesis.

Pair this enzyme with its activator: N-acetylglutamate synthtase (NAGs)

activated by arginine. NAG activates CPS1 in the ura cycle

Several amino acids are intermediates of the urea cycle. Which one of the following amino acids has a nitrogen in its side chain and is an intermediate of the urea cycle.

arginine.

Under fasting conditions, acetyl-CoA carboxylase will be inhibited by an increase in which of the following compounds?

fatty acyl-CoA Lipolysis is active, increase in fatty acyl-CoA in the cell for the process of β-oxidation will decrease citrate and activity of acetyl-CoA carboxylase.

Acyl carrier protein (ACP) requires what for activity?

pantothenic acid (CoA)

A 40 yr old male has pain in his big toe and is diagnosed with gout. Allopurionol is administered to inhibit which one of the following enzymes?

xanthine oxidase Allopurinol is a xanthine oxidase inhibitor. By reducing the activity of this enzyme, this will reduce uric acid production.