UNE MBS 650: Applied Medical Biochemistry (Midterm - Units 1-2)

Which of the following proteins is likely to have quaternary structure?

A multimeric protein that contains multiple peptide chains

__________ is considered the most common secondary structure, while __________ is considered the most stable of the secondary structures.

α-helix, β-sheet

Which of the following is the best description of primary protein structure?

A newly synthesized strand of amino acids

A β-sheet of amino acids is considered to be part of what level of protein structure?

Secondary structure of the protein

A 22-year-old female presents to the emergency department with acute abdominal pain. She indicates the pain came on rapidly in her mid-abdominal region. She has vomited several times over the last 4 hours. A diagnosis of acute pancreatitis is made. Elevation of which of the following serum enzymes would be consistent with this diagnosis?

Amylase

Many enzymes use covalent catalysis to cleave peptide bonds. Which of the following amino acids would not facilitate this type of catalysis? (Think of the structure of the R-group of these amino acids)

Valine

Cleavage of fructose 1,6-bisphosphate to dihydroxyacetone and glyceraldehyde 3-phosphate is achieved by what class of enzymes?

Lyase

A newly characterized enzyme is determined to catalyze the transfer of functional groups. Based on this information, it most likely belongs to which enzyme family?

Transferases

An unknown protein is isolated and is being structurally characterized. It appears to have several secondary structures. These structures are predominantly stabilized by which of the following bonds or forces?

Hydrogen bonds

Changes in the physiological variables listed below can alter hemoglobin's affinity for oxygen. Which of the following will increase the affinity of hemoglobin for oxygen?

Increase in pH

Which of the following does not aid in stabilizing the tense state of hemoglobin?

Carbon monoxide

In the R state, all four subunits of hemoglobin exhibit a __________ affinity for oxygen. In the T state, all four subunits exhibit a __________ affinity for oxygen.

High, low

Hemoglobin bound to heme is termed a holoprotein. The heme group (or porphyrin ring) is required for oxygen binding and it is defined as which of the following?

Prosthetic group

A pharmaceutical firm is investigating the effects of a novel drug on hemoglobin. The plot for this enzyme shows a sigmoidal relationship between substrate concentration ([S]) and initial reaction velocity (Vi). A sigmoidal plot indicates which of the following?

Cooperative binding

A 45-year-old man is brought into the emergency department suffering from apparent alcohol intoxication. The patient is experiencing metabolic acidosis as well as severe stomach and intestinal distress. Further analysis reveals that the patient accidentally ingested methanol or wood alcohol. To reverse the toxic effects of methanol, the patient receives a dose of ethanol, a competitive inhibitor of alcohol dehydrogenase. If you are monitoring ADH activity in this patient, which of the following would you expect to find?

Increase in the apparent Km but no change in the Vmax

Which of the following can NOT be found on the Michaelis-Menten graph?

1/Vmax

A 28-year-old male is recently diagnosed with HIV. As part of his treatment, he is prescribed Nevirapine, which interferes with the retroviral reverse transcriptase enzyme. Using the graph below, which of the following best describes the impact of this drug on its target?

It reduces the catalytic activity of the enzyme

With respect to Michaelis-Menten kinetics, the addition of a noncompetitive inhibitor to a reaction would result in which of the following?

No change in Km and a decrease in Vmax

How does ΔG, the overall change in free energy for a reaction, depend on the reaction mechanism?

It is independent of the reaction mechanism

Children with cystinosis have growth delay and both renal and ocular issues due to the accumulation of cystine in cellular lysosomes. Effective therapy has been the administration of a drug with a structure similar to cystine. This therapy reflects the general principle that competitive inhibitors typically resemble the structure of which of the following?

Substrates or ligands that bind to the active site

Why do the cellular concentrations of substrates for most enzymes tend to be close to Km?

To maximize the production of products

The association of DNA and histones can be modified by histone acetylation. An increase in histone acetylation will have which of the following impacts on the association of DNA and histones?

Decrease DNA: histone association

What is the advantage of measuring the velocity of an enzyme-catalyzed reaction under initial rate conditions?

It minimizes the effect of product inhibition

Enzymes help reduce the transition state energy of a reaction by each of the following:

Stabilizing the substrate within the active site, using cofactors to help with group transfer, and stabilizing the enzyme-substrate transition state

Each of the following amino acids has an exposed hydroxyl group that can be phosphorylated:

Serine, threonine, tyrosine

An unknown compound is added to a reaction. Overall, the reaction's Vmax decreases, but the enzyme's Km remains unchanged. This compound is best defined as which of the following?

Noncompetitive inhibitor

Which of the following is an example of enzyme regulation through covalent modification?

Phosphorylation of muscle glycogen phosphorylase

In an experiment, a researcher adds an allosteric effector. Which of the following best characterizes how this compound will influence catalytic activity?

By changing the conformation of the enzyme's active site

Competitive inhibitors typically resemble __________.

Substrates

Dinitrophenol is an uncoupler of the electron transport chain. The addition of dinitrophenol will have which of the following impacts?

Increase oxygen consumption

Dinitrophenol is an uncoupler of the electron transport chain. Adding dinitrophenol will have which of the following effects on the cell?

2

Complex II (Succinate Q-reductase) is not considered to be part of the process of oxidative phosphorylation because it is unable to do which of the following activities?

Pump protons from the mitochondrial matrix to the intermembrane space

During the synthesis of ATP, which of the following is a proton pump?

Complexes I, III, and IV

The glycerol 3-phosphate shuttle is the major shuttle in most tissues. Which of the following best describes the transfer of electrons by this shuttle?

Electrons are directly transferred from glycerol 3-phosphate to an FAD-containing glycerol phosphate dehydrogenase

An inhibitor of Complex I would directly impact which of the following functions of the electron transport chain?

The transfer of electrons from NADH to coenzyme Q

In the malate aspartate shuttle, glutamate is converted to _________ in the mitochondria while aspartate is converted to ___________ in the cytosol.

α-ketoglutarate; oxaloacetate

The system is at equilibrium when ΔG is __________.

Zero

If ΔG is positive, the reaction proceeds only if free energy can be gained and is __________.

Endergonic

Which of the following statements best describes the process of oxidative phosphorylation?

ATP is produced from ADP and Pi using a proton gradient

Which of the following components of the electron transport chain are bound to the mitochondrial membrane?

Complexes I-V (NADH Q-oxidoreductase, succinate Q-reductase, Q-cyt C oxidoreductase, cytochrome C oxidase, ATP synthase)

The malate-aspartate shuttle is used to move reducing equivalents of cytosolic NADH into the mitochondria, where it can be oxidized. Which of the following compounds is used to move the reducing equivalents of cytosolic NADH into the mitochondria?

Malate

Which of the following is a major source of ATP production?

Oxidative phosphorylation, TCA cycle, glycolysis

A newly characterized enzyme is determined to be part of cellular respiration. Based on this information, this enzyme is most likely located in which subcellular location?

Inner mitochondrial membrane

Inhibitors of the respiratory chain are responsible for which of the following?

Decrease in NADH oxidation, oxygen consumption, and overall ATP production

ATP carries energy within the cell. The majority of the energy in ATP is stored in which of the following bonds indicated in the image below?

1

How does Complex II function in the electron transport chain?

It transfers electrons from FADH2 to coenzyme Q

A 19-year-old male is being evaluated for muscle weakness. A muscle biopsy showed normal rates of succinate oxidation but very low rates of pyruvate oxidation. Further testing showed normal enzymatic activity in both malate dehydrogenase and pyruvate dehydrogenase. Based on this data, the patient may have a mutation in a gene encoding for which mitochondrial protein?

Complex I (NADH Q-oxidoreductase)

Which of the following is a major difference between myoglobin and hemoglobin?

Hemoglobin carries oxygen, while myoglobin stores it

What is meant by induced fit in enzyme activity?

The enzyme changes shape to better fit the substrate

Movement of ammonia from an amino acid to an α-keto acid involves a family of enzymes best categorized as which of the following?

Transferases

Which of the following proteins will likely be the most stable and have the lowest energy state?

A structure with a high content of β-sheets

Allosteric inhibitors of hemoglobin will decrease enzyme activity (oxygen binding) through which of the following mechanisms?

Binding the enzyme and keeping it in the "T" conformation

In the conversion of trypsinogen (proenzyme) to trypsin (active form), what structural change has occurred?

Cleavage of a specific peptide bond

Use the figure below to compare the activities of glucokinase and hexokinase. Based on this information, which of the following is a true statement?

Glucokinase has a higher Km than hexokinase.

The following represents a series of reactions. As S2 levels increase, C production increases. Which of the following best describes this type of regulation in a biosynthetic pathway?

Feedforward activation

An enzyme is participating in a general acid-base catalysis reaction. If acid is added to the environment, reducing the pH to 3, what is the likely impact on the rate of reaction?

The rate of the reaction is likely to decrease as the pH is outside the optimal catalytic range

Which of the following enzymes is part of both the TCA cycle and the electron transport chain?

Succinate dehydrogenase (Complex II)

When calculating ΔG, all the following are needed except:

Mass

According to the first law of thermodynamics, the energy of a system is __________.

Constant

During oxidative phosphorylation the proton pumps create a proton gradient across the membrane that is negative on the ______________ side.

Matrix

Many digestive enzymes and hormones are synthesized as proenzymes. Which of the following best describes why this is advantageous?

It prevents premature activity

In utilizing the Michaelis-Menten equation, velocity (vi) and the Michaelis constant (Km) are __________ related.

Inversely

Which of the following best describes an enzyme inhibitor that increases the Km but does not change the Vmax?

A competitive inhibitor

Allosteric effectors bind to a site __________.

On the enzyme but not at the active site.

Which of the following amino acids would not be commonly found in the middle of an α-helix?

Proline

An unknown protein is isolated and is being structurally characterized. Based on preliminary results, it appears to have a significant number of secondary structures that have a consistent spiral shape. These structures are most likely representative of which of the following secondary structures?

Alpha helix

A 55-year-old male is brought to the emergency department with a chief concern of chest pain and tingling in his left arm. Elevation of which of the following enzymes in circulation would be most indicative of a myocardial infarction?

Troponin

Which of the following best defines catalysis by proximity?

Catalysis through increasing the concentration of reactants in the enzyme active site

Which of the following is an insulin-insensitive GLUT transporter found primarily in the liver?

GLUT2

A suspected mutation in the cortisol receptor is discovered. Cortisol can still bind its receptor, but the dimerized complex remains in the cytosol. Based on this description, which region of the receptor is likely impacted?

Nuclear localization signal

You and several friends share a large pizza. Immediately afterward, which of the following GLUT transporters is primarily responsible for the uptake of glucose in skeletal muscle?

GLUT4

Which of the following is true of the fasted state?

Muscle tissue preferentially takes up and oxidizes fatty acids for fuel

Order the following statements to illustrate the correct cascade of events that occurs after ligand binding of a G protein-coupled receptor (heptahelical receptor):

1. Degradation of cAMP by phosphodiesterase

2. Dissociation of Gβ and Gγ subunits

3. G protein exchanges GDP for GTP in the G-αs subunit

4. Activation of adenylyl cyclase (effector E) to generate cAMP

3, 2, 4, 1

A young woman goes to work without eating breakfast and skips lunch. In this scenario, which of the following pathways provides substrates used to generate ATP in the liver?

Free fatty acids

After a 24-hour fast, which of the following is the major metabolic pathway providing an oxidizable substrate for the skeletal muscle?

Lipolysis

A teenager presenting with a lack of menstruation (amenorrhea) is found to have a dysfunctional steroid receptor characteristic of androgen insensitivity syndrome. Which of the following statements accurately describes steroid hormones?

They enhance transcription when bound to receptors

Shortly after a meal, there will be increased activity in which of the following pathways as a result of increased insulin?

Glycolysis

Following insulin binding to its receptor and autophosphorylation of the β- chain, what is the initial step in this cascade of events?

Recruitment of the insulin receptor substrate (IRS)

Steroid hormones bind to which of the following types of receptors?

Intracellular receptors

Which of the following would not be found in the insulin signaling cascade?

Adenylyl cyclase

Insulin is a major metabolic hormone. Its primary role on metabolism is best summarized by which of the following statements?

It promotes fuel storage and growth after a meal

In the event that PI-3 kinase is not activated downstream of insulin, which of the following proteins would not be able to dock to the membrane?

Protein Kinase B

Which of the following pathways directly provides an oxidizable substrate to red blood cells during the fasted state?

Hepatic glycogenolysis

Consuming a high-carbohydrate diet can lead to weight gain. Intermediates in the conversion of dietary glucose to fatty acids include:

Pyruvate, fructose 6-phosphate, and acetyl-CoA

Pyruvate can be directly converted into which of the following amino acids?

Alanine

Which of the following reactions is commonly used to replenish intermediates of the TCA cycle?

Glutamate → α-ketoglutarate

Which of the following intermediates of the TCA cycle is required in the cytosol for fatty acid synthesis?

Citrate

A patient presents with a thiamine deficiency. If this patient's liver cells are compared with normal cells, which of the following products would be decreased in the thiamine-deficient cell (when compared to the normal cells) if the cells are only given glucose as a fuel?

CO₂

A farmer finds a cow dead in his field and notices an unusual plant nearby. Autopsy results show an elevated level of citrate present in the cow's mitochondria. This data collectively suggests inhibition of which of the following enzymes?

Aconitase

Pyruvate dehydrogenase kinase catalyzes a reaction that results in which of the following?

The phosphorylation and inactivation of the E1 subunit of the PDC (pyruvate dehydrogenase complex)

Which of the following correctly pairs the amino acid with the TCA cycle intermediate it can be transaminated to?

Glutamate: α-ketoglutarate

Which of the following intermediates of the TCA cycle is required in the cytosol for fatty acid synthesis?

Citrate

In the liver, the pyruvate dehydrogenase complex (PDC) would be dephosphorylated and active when which of the following compounds or hormones is elevated?

Pyruvate

NADH generated in the cytosol must be transported across the mitochondrial membrane in order to be oxidized by the electron transport chain. Which of the following shuttles or transporters can be used to facilitate the movement of cytosolic NADH into the mitochondria?

Glycerol 3-phosphate shuttle

A 10-year-old male is playing soccer and is sprinting after the ball. Under these anaerobic conditions, glucose is primarily oxidized to which of the following compounds?

Lactate

An individual consumes a breakfast consisting of cereal, eggs, sausage, pancakes, and maple syrup. After this meal, which of the following statements best summarizes his metabolic state?

Fructose 2,6-bisphosphate will be elevated

Certain conditions, such as excessive alcohol consumption, can increase the ratio of NADH/NAD+ in the mitochondria. The elevated levels of NADH will directly inhibit which of the following enzymes?

α-ketoglutarate dehydrogenase

After a meal, fructose 2,6-bisphosphate levels are elevated. This compound allosterically activates which of the following glycolytic enzymes?

Phosphofructokinase-1(PFK1)

Several key regulatory enzymes are involved in gluconeogenesis. Which of the following answers lists these enzymes in the correct order in which they are used for glucose production?

Pyruvate carboxylase; phosphoenolpyruvate carboxykinase (PEPCK); Fructose 1,6-bisphosphatase

The process of gluconeogenesis primarily takes place in which of the following tissues?

Liver