[Biochem A] Prelims to Midterms Samplex

Activation of trypsinogen to trypsin, with subsequent autocatalysis and activation of other zymogens, illustrates what type of enzyme regulation?

Covalent modification

In the figure below, which of the following energy is changed by an enzyme? [energy]

B

In the figure below, which of the following will require more substrate to reach Vmax? (only 3 choices) [km]

Enzyme 2

In the figure below, which point represents the saturation of the enzyme’s active sites during the chemical reaction? (only 3 choices) [reaction order]

Point C

Methylmalonyl-CoA mutase catalyzes the rearrangement of methylmalonyl-CoA to succinyl-CoA. This enzyme belongs to which class of enzymes?

Isomerase

Pravastatin, an antidyslipidemic agent that lowers LDL, competes with HMG-CoA for binding at the active site of HMG-CoA reductase. This is an example of which type of enzyme inhibition? 

Competitive

Shown in the figure below is a double reciprocal plot for an experimental drug that lowers blood pressure. Which of the following is INCORRECT regarding the drug? [lineweaver]

Adding more substrate to the enzyme catalyzed reaction will eventually overcome the inhibition reaching Vmax.

Special area in an enzyme where substrates, cofactors, and aminoacyl side chains are brought in close proximity with each other.

Active site

These are small organic molecules that are tight and stably incorporated in the enzyme's structure.

Prosthetic group

This enzyme type catalyze formation of bonds between carbon and -O, -S, and -N coupled to hydrolysis of high energy phosphate such as ATP.

Ligase

This is an enzyme without its nonprotein moiety.

Apoenzyme

Time required for change is hours to day for which type of regulator event?

Enzyme degradation

Which conformational model of enzyme action is analogous to a hand fitting into a glove, inducing a dynamic change in the active site of the enzyme?

Daniel Koshland theory

Which of the 4 mechanistic strategies during catalysis applies to enzyme HIV protease?

Acid-base catalysis

Which of the following CORRECTLY describes competitive inhibition

All of the choices are correct.

Which of the following is TRUE regarding the Michaelis constant

Lower Km will need fewer substrate to reach half maximal velocity.

Which of the following regulatory events typically uses another enzyme as its effector?

Covalent modification

Which of the following statement is TRUE regarding ribozymes?

All of the choices are correct.

Which of the following statement is TRUE regarding the effects of temperature in enzyme kinetics?

Most human enzymes generally exhibit stability up to 55 degree celsius.

Which of the mechanistic strategies during catalysis is common in group transfer reactions?

Covalent catalysis

A patient is exposed to a pesticide that inhibits Complex I of the ETC. Which metabolic consequence is MOST LIKELY?

NADH oxidation in the mitochondria will be impaired, reducing proton pumping and ATP yield.

A toxin blocks proton flow through ATP synthase but does not affect electron transfer in the ETC. Which immediate effect will occur

Proton gradient will build up, halting electron flow as back pressure increases.

Complete oxidation of one glucose molecule yields 10 NADH and 2 FADH₂ from glycolysis, pyruvate oxidation, and the TCA cycle. How many ATPs are produced from these reducing equivalents in oxidative phosphorylation?

28 ATP

During aerobic respiration, FADH₂ produces fewer ATP than NADH. Which explanation is MOST ACCURATE

FADH₂ oxidation bypasses Complex I, leading to fewer protons pumped across the membrane.

If malonate is present, which of the following processes will be inhibited?

Conversion of succinate to fumarate

If oxygen is unavailable, which statement best explains why oxidative phosphorylation stops?

Oxygen is required as the final electron acceptor, halting proton pumping.

If the ∆G° for the hydrolysis of ATP is -30.5 kJ/mol, what does this imply about ATP’s role in metabolism?

ATP hydrolysis is strongly exergonic and can drive endergonic cellular reactions.

In the Krebs cycle, ATP (or GTP) is directly formed during the conversion of which substrate to its corresponding product?

Succinyl-CoA → Succinate

In thermodynamic terms, why is oxidative phosphorylation dependent on the ETC?

It generates a proton-motive force that couples electron flow to ATP synthesis.

The malate-aspartate shuttle indirectly increases ATP yield per glucose molecule by which of the following mechanism?

Allowing NADH from glycolysis to transfer electrons into mitochondria without loss of energy yield

What is the functional role of Fe–S clusters in Complex I and Complex II? They-

mediate stepwise electron transfers to CoQ

Which BEST describes the role of Complex III in energy transduction?

Pumps protons while shuttling electrons from coenzyme Q to cytochrome c

Which ETC component can move freely within the lipid bilayer to transfer electrons between complexes?

Ubiquinone

Which is CORRECT regarding the glutathione peroxidase anti-oxidant system?

It is dependent on adequate levels of reduced glutathione.

Which of the following is NOT a substrate-level phosphorylation reaction?

Isocitrate → α-Ketoglutarate

Which of the following statements about ATP is LEAST consistent with its role as a central energy carrier in metabolism?

ATP is a more stable form than ADP and inorganic phosphate, which explains its accumulation in cells.

Which pathway produces ATP without the involvement of an electron transport chain?

Both A and B

Which statement best describes the dual role of succinate dehydrogenase? A. It oxidizes succinate to fumarate in glycolysis and pumps protons in

It is part of the Krebs cycle and transfers electrons directly to ubiquinone in the ETC.

Which statement is TRUE regarding proton pumping by ETC complexes?

Complex III pumps protons during the Q-cycle.

Why does blocking Complex IV cause electron flow through the ETC to stop completely?

Oxygen is needed to oxidize cytochrome c and maintain electron flow.

A diet high in raffinose and stachyose causes bloating. Which biochemical fact explains this symptom?

They are fermented by gut bacteria.

A newborn with galactosemia cannot metabolize galactose. Which dietary change will prevent symptom progression?

Remove lactose-containing foods

A patient has difficulty digesting milk but tolerates maltose-containing foods. Which enzyme deficiency is most likely?

Lactase

A patient is given a disaccharide load test and develops diarrhea after ingesting sucrose but not maltose. Which enzyme is deficient?

Sucrase

A patient with a connective tissue disorder has reduced hyaluronic acid in the extracellular matrix. Which monosaccharide components are directly affected?

D-glucuronate and N-acetyl-D-glucosamine

A researcher isolates a polysaccharide with β-1,4 linkages of N-acetylglucosamine. Which of the following is most likely its function?

Exoskeleton structural component

A sugar that rotates plane-polarized light to the right is described as:

Dextrorotatory

A β-1,4 glycosidic linkage in cellulose makes it indigestible to humans because they lack which enzyme?

Cellulase

Which of the following processes leads to the breakdown of glycogen into glucose units , during exercise?

Phosphorolysis of α-1,4 bonds

Epimers differ from each other in which characteristic?

Configuration at only one specific chiral carbon.

In a Haworth projection of glucose, where is the OH group at the anomeric carbon positioned, in the alpha anomer?

Below the plane of the ring

Which of the following explains, the changes in optical rotation of glucose in solution until it reaches an equilibrium point?

Interconversion between α and β anomers

What is the classification of raffinose, stachyose, and verbascose?

Oligosaccharides

Which of the following describes stereo isomers that are neither mirror images of each other or differs from one another at only 1 chiral carbon?

Diastereomers

Which of the following determines the ABO blood group antigens?

Terminal monosaccharide in the oligosaccharide chain of glycoproteins

The glycosidic bond in maltose links two glucose molecules via which carbons?

α-1,4

The number of possible stereoisomers of a carbohydrate is calculated using which formula? (where n is the number of chiral carbons)

2ⁿ

What is the difference between the α and β forms of glucose?

The position of the OH group at the anomeric carbon

Which of the following describes two sugars having the same chemical formula but differ in configuration at C-4 only?

Epimers

Which amino sugar is formed from glucose via specific enzymatic modification?

Glucosamine

Which disaccharide consists of glucose + galactose?

Lactose

Which of the following best defines a carbohydrate?

Polyhydroxy aldehyde or ketone

Which of the following is the main storage form of carbohydrates in animals?

Glycogen

Which polysaccharide is composed of D-glucuronic acid and N-acetyl-D-glucosamine repeating units?

Hyaluronic acid

Which structural feature allows glycogen to be more readily mobilized(produces glucose faster) than starch?

Highly branched α-1,6 linkages

Which enzyme catalyzes the major anaphlerotic reaction in the body?

Pyruvate carboxylase

Measurement of the transketolase level in the erythrocyte provides an index of the nutritional status of what vitamin?

Thiamine

Which enzyme of the PPP provides ribose 5-phosphate for the synthesis of purine and pyrimidine nucleotides?

Ribose-5-phosphate ketoisomerase

How many moles of ATP are produced thru oxidative phosphorylation if one mole of isocitrate goes thru the citric acid cycle?

9

Which reactions is NOT a control point in the Krebs cycle?

Malate ------> Oxaloacetate

If the energy requirement of the cell is low, what happens?

ATP/AMP ratio is high

This enzyme catalyzes an irreversible substrate level phosphorylation reaction in the glycolytic pathway.

Pyruvate kinase

Which statement/s is/are TRUE regarding the reactions that occur in glycolysis?

Conversion of glucose-6-PO4 to fructose-6-PO4 is an isomerization reaction

If pyruvate enters the Krebs cycle thru Acetyl CoA, how many moles of ATP will be produced?

12.5

Together with glucose-6-phosphatase and fructose-1,6-bisphosphatase, which bypass enzymes are used if Histidine is converted to glucose?

Phosphoenolpyruvate carboxykinase

What are the effects of the substance produced if Phosphofructokinase 2 is the enzyme used in the 3rd step of glycolysis?

stimulates phosphofructokinase 1, inhibits fructose-1,6-bisphosphatase

Which of these statements correctly differentiate hexokinase and glucokinase?

All statements are correct

If phosphoenolpyruvate undergoes complete oxidation, how many moles of ATP will be produced?

13.5

Which is the only oxidation step in the glycolytic pathway?

Glyceraldehyde 3-phosphate, 1,3-bisphosphoglycerate

If glucose goes thru glycolysis, how many ATPs are produced thru substrate level phosphorylation up to the 7th reaction of glycolysis?

2

Which of the following statements is/are CORRECT?

All are correct

What kind of reaction is catalyzed by Phosphofructokinase 1?

Phosphoryl transfer

Number of ATPs invested if one mole of glucose-6-phosphate undergoes aerobic glycolysis using the glycerol phosphate shuttle.

1

What is the only reaction in the Krebs’ cycle which is substrate level phosphorylation?

Succinyl CoA → succinate

Which of these are pathways that lower the blood sugar level?

Glycolysis and Glycogenesis

What are the effects of epinephrine?

Stimulates liver and muscle glycogenolysis

If one mole of dihydroxyacetone phosphate undergoes complete oxidation, using the malate aspartate shuttle, how many moles of ATP will be produced thru oxidative phosphorylation alone?

14

What happens if Thiamine is deficient?

All of the above

Which of the following statements is/are TRUE regarding the Pentose phosphate pathway?

Only A and C are correct

A 21-year old woman suffering from severe colds had a very poor appetite and had not eaten more than 300 calories per day for the past 3 days. By the third day, which of the following enzymes is playing a key role in the synthesis of her plasma glucose?

PEPCK

Which of the following is/are effect/s of glucagon?

Only A and C are correct

Number of ATPs produced thru substrate level phosphorylation alone if one mole of glucose undergoes complete oxidation?

6

Which enzyme in the uronic acid pathway is NOT PRESENT in man that’s why man cannot synthesize Vitamin C from glucose?

Gulonolactone oxidase

Deficiency of which enzymes can lead to hemolytic anemia?

Pyruvate kinase and cleavage enzyme

Which of these statements correctly describes Glucose-6-phosphatase?

It is a bypass enzyme of gluconeogenesis

Which of these reactions releases NADPH in the Phosphogluconate shunt?

A and C only

Given a patient suffering from biotin deficiency. Which reaction will NOT take place in the patient?

Major anaphlerotic reaction

Which of these enzymes are stimulated by epinephrine, both directly and indirectly?

I. Glycogen phosphorylase

II. PEPCK

III. Adenylate cyclase

IV. Fructose-1,6-bisphosphatase

D- I, II, III, IV are correct

Which of these pathways are stimulated by insulin?

I. glycolysis

II. glycogenolysis

III. lipogenesis

IV. gluconeogenesis

B – if only I and III are correct

Which of these pathways are stimulated when the level of AMP and ADP high?

I. Embden-Meyerhof-Parnas pathway

II. Glycogenolysis

III. Citric acid cycle

IV. Gluconeogenesis

B – if only I and III are correct