Enzymes Regulation Questions and Answers

Q: “Ping Pong” reaction is the other name for

Correct answer: Double-displacement bi-substrate reactionIn a ping-pong mechanism the first substrate binds, part of it is transferred to the enzyme, and the first product leaves before the second substrate arrives - hence “double displacement”, and hence the name. The transaminases work this way, with the amino group parked on the enzyme’s pyridoxal phosphate between the two half-reactions.

Q: The inactive protein part of an enzyme is the

Correct answer: apoenzymeAn apoenzyme is the protein part alone, and it is catalytically inactive. Add the cofactor - a metal ion or a coenzyme - and the complete, active holoenzyme results.

Q: The viscosity of blood increases with a rise in ________ levels

Correct answer: AlbuminPlasma viscosity rises with the concentration of plasma protein, and albumin is much the most abundant of them - some 60% of the total - so it accounts for most of the effect by sheer quantity. (Fibrinogen, being a long asymmetrical molecule, raises viscosity disproportionately for its concentration; and the largest single determinant of whole-blood viscosity is the haematocrit.)

Q: How many types of enzyme regulation mechanism occur in cells?

Correct answer: 5Cells regulate enzymes in five main ways: allosteric control, covalent modification (phosphorylation and the rest), proteolytic activation of zymogens, the use of isoenzymes, and control of the amount of enzyme present by induction and repression. They differ chiefly in speed - allosteric control acts in milliseconds, induction over hours.

Q: Which type of enzyme inhibition shows a decreased Km value?

Correct answer: Un-competitive inhibitionAn uncompetitive inhibitor binds only to the enzyme-substrate complex, never to the free enzyme. Removing ES from the equilibrium pulls more substrate into binding, so the enzyme appears to have greater affinity and \(K_m\) falls - while \(V_{max}\) falls too, since the trapped complexes cannot turn over. Competitive inhibition does the opposite, raising \(K_m\).

Q: In sickle cell anaemia the defect lies in which polypeptide chain?

Correct answer: β-chainSickle cell anaemia is a single point mutation in the β-globin gene: glutamic acid is replaced by valine at position 6. The substitution puts a hydrophobic patch on the surface, so deoxygenated haemoglobin S molecules polymerise into fibres that distort the cell into a sickle. Because the β chain is not made until after birth, the disease does not appear in the first months of life.

Q: Average RBC count in an adult male is

Correct answer: 5.5 million/mm³An adult male has about 5.5 million red cells per cubic millimetre, an adult female about 4.8 million. The difference is largely the effect of testosterone on erythropoiesis, reinforced by menstrual iron loss.

Q: Allosteric enzymes possess

Correct answer: Active site and an allosteric siteThe defining arrangement is two distinct sites: an active site where the substrate is bound and converted, and a separate allosteric site where the modulator binds. Allosteric means “other site”, and the whole mechanism depends on the two being different places on the molecule.

61.

“Ping Pong” reaction is the other name for

A. Single-substrate reaction
B.Single-displacement bi-substrate reaction
C.Double-displacement bi-substrate reaction
D.Sequential bi-substrate reaction

Answer: C

Correct answer: Double-displacement bi-substrate reaction

In a ping-pong mechanism the first substrate binds, part of it is transferred to the enzyme, and the first product leaves before the second substrate arrives - hence “double displacement”, and hence the name. The transaminases work this way, with the amino group parked on the enzyme’s pyridoxal phosphate between the two half-reactions.

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62.

The inactive protein part of an enzyme is the

A.apoenzyme
B.enzyme
C.holoenzyme
D.cofactor

Answer: A

Correct answer: apoenzyme

An apoenzyme is the protein part alone, and it is catalytically inactive. Add the cofactor - a metal ion or a coenzyme - and the complete, active holoenzyme results.

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63.

The attachment of phosphoryl groups to specific amino acid residues is catalyzed by ___________

A.Diphteria toxin and cholera toxin
B.Dinitrogenase reductase
C.Protein phosphatases
D.Protein kinases

Answer: D

The enzymes that catalyse the ADP-ribosylation and inactivation of key cellular enzymes or proteins are diphteria toxin and cholera toxin. Dinitrogenase reductase is responsible for the regulation of biological nitrogen fixation. Removal of phosphoryl groups is catalyzed by Protein phosphatases.

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64.

The viscosity of blood increases with a rise in ________ levels

A.Albumin
B.Globulin
C.Fibrinogen
D.Prothrombin

Answer: A

Correct answer: Albumin

Plasma viscosity rises with the concentration of plasma protein, and albumin is much the most abundant of them - some 60% of the total - so it accounts for most of the effect by sheer quantity. (Fibrinogen, being a long asymmetrical molecule, raises viscosity disproportionately for its concentration; and the largest single determinant of whole-blood viscosity is the haematocrit.)

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65.

How many types of enzyme regulation mechanism occur in cells?

Answer: D

Correct answer: 5

Cells regulate enzymes in five main ways: allosteric control, covalent modification (phosphorylation and the rest), proteolytic activation of zymogens, the use of isoenzymes, and control of the amount of enzyme present by induction and repression. They differ chiefly in speed - allosteric control acts in milliseconds, induction over hours.

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66.

Which type of enzyme inhibition shows a decreased Km value?

A.Competitive inhibition
B.Un-competitive inhibition
C.Non-competitive inhibition
D.Feed back inhibition

Answer: A

Correct answer: Un-competitive inhibition

An uncompetitive inhibitor binds only to the enzyme-substrate complex, never to the free enzyme. Removing ES from the equilibrium pulls more substrate into binding, so the enzyme appears to have greater affinity and \(K_m\) falls - while \(V_{max}\) falls too, since the trapped complexes cannot turn over. Competitive inhibition does the opposite, raising \(K_m\).

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67.

In sickle cell anaemia the defect lies in which polypeptide chain?

A.α-chain
B.β-chain
C.γ-chain
D.δ-chain

Answer: B

Correct answer: β-chain

Sickle cell anaemia is a single point mutation in the β-globin gene: glutamic acid is replaced by valine at position 6. The substitution puts a hydrophobic patch on the surface, so deoxygenated haemoglobin S molecules polymerise into fibres that distort the cell into a sickle. Because the β chain is not made until after birth, the disease does not appear in the first months of life.

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68.

Average RBC count in an adult male is

A.4.5 million/mm³
B.5 million/mm³
C.5.5 million/mm³
D.6 million/mm³

Answer: C

Correct answer: 5.5 million/mm³

An adult male has about 5.5 million red cells per cubic millimetre, an adult female about 4.8 million. The difference is largely the effect of testosterone on erythropoiesis, reinforced by menstrual iron loss.

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69.

MCHC is the

A.Volume of single RBC
B.Average amount of haemoglobin in a single RBC in picogram
C.Average amount of haemoglobin in a single RBC in percentage
D.never less than 38%

Answer: C

Correct answer: Average amount of haemoglobin in a single RBC in percentage

MCHC is the mean corpuscular haemoglobin concentration - haemoglobin per unit volume of packed cells, expressed as a percentage or as g/dL:

\[ \text{MCHC} = \frac{\text{Hb}}{\text{PCV}} \times 100 \]

It is the one index that does not depend on cell size. The amount per cell in picograms is the MCH, a different measure.

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70.

Allosteric enzymes possess

A.Three types of allosteric sites
B.Active site and three types of allosteric sites
C.Active site and two types of allosteric sites
D.Active site and an allosteric site

Answer: D

Correct answer: Active site and an allosteric site

The defining arrangement is two distinct sites: an active site where the substrate is bound and converted, and a separate allosteric site where the modulator binds. Allosteric means “other site”, and the whole mechanism depends on the two being different places on the molecule.

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