Isoenzymes

ISOENZYMES

Q. 1

True about isoenzymes is:

 A

Same quaternary structure

 B

Same distribution in different organs

 C

Same enzyme classification with same umbers

 D

Catalyze the same reaction

Q. 1

True about isoenzymes is:

 A

Same quaternary structure

 B

Same distribution in different organs

 C

Same enzyme classification with same umbers

 D

Catalyze the same reaction

Ans. D

Explanation:

    • Isoenzymes are the multiple forms of the same enzyme in a single species that catalyze the same chemical reaction or reactions, but differ from each other structurally, electrophoretically and immunologically.
    • Though the same chemical reaction is catalyzed, the different isoenzymes may catalyze the same reaction at different rates.
    • Isoenzymes have different pH optimes, Km and V max values.
    • Isoenzymes may differ in their amino acid sequence and their quarternary structures.
    • The isoenzymes may have different properties also for e.g. LDH-4 and LDH-5 are easily destroyed by heat, whereas LDH-1 and LDH-2 are not, if heated upto 60°C. (Heat resistant).
    • Individual isoenzymes (isozymes) are distinguished and numbered on the basis of electrophoretic mobility, with the number 1 being assigned to that form having the highest mobility toward the anode, for e.g. LDH-1 has the highest mobility towards the anode and LDH-5 is the slowest.
    • Isoenzymes have different tissue distributions. Therefore the pattern of isoenzymes found in the plasma may serve as a means of identifying the site of tissue damage. Example of the diagnostic use of isoenzymes are the study of Lactate Dehydrogenase and Creatine Kinase.

Q. 2

True about isoenzymes is/are:

 A

Different km value

 B

Act on different substrate

 C

Same electrophoretic mobility

 D

All

Q. 2

True about isoenzymes is/are:

 A

Different km value

 B

Act on different substrate

 C

Same electrophoretic mobility

 D

All

Ans. A

Explanation:

  • Isozymes are the physically distinct forms of the same enzymes that catalyze the same reaction, and differ from each other structurally, electrophoretically and immunologically.
  • They differ in their physical properties because of genetically determined difference in amino acid sequence.
  • They are separated by electrophoresis as they have different electrophoretic mobility.
  • They have different Km value.
  • Isoenzyme of an oligomeric enzyme process differ in combination of its peptide protomer.

Q. 3

Which isoenzyme of LDH is seen in heart

 A

LDH 1

 B

LDH 2

 C

LDH 3

 D

LDH 4

Q. 3

Which isoenzyme of LDH is seen in heart

 A

LDH 1

 B

LDH 2

 C

LDH 3

 D

LDH 4

Ans. A

Explanation:

Ans. is ‘a’ i.e., LDH1

Quiz In Between


Q. 4

First enzyme to be raised in MI is ‑

 A

CPK-MB

 B

LDH

 C

Myoglobin

 D

Troponin-I

Q. 4

First enzyme to be raised in MI is ‑

 A

CPK-MB

 B

LDH

 C

Myoglobin

 D

Troponin-I

Ans. C

Explanation:

Ans. is ‘c’ i.e., Myoglobin 


Q. 5

Enzyme specificity is given by ‑

 A

Km

 B

Vrm„

 C

Both

 D

None

Q. 5

Enzyme specificity is given by ‑

 A

Km

 B

Vrm„

 C

Both

 D

None

Ans. A

Explanation:

Ans. is ‘a’ i.e., K. 

  • The Km of an enzyme is the concentration of the substrate that enables the enzyme to function at half maximum activity and is therefore a measure of the specificity of a substrate.for the enzyme” Clinical biochemistry
  • Actually enzyme specificity is not measured by Km alone.
  • It is measured by the ratio Kcat/Km which is a second order rate constant for the reaction between substrate and free enzyme.
  • This ratio is important, for it provides a direct measure of enzyme efficiency and specificity.
  • Note : Kcat is turnover number and measures the rate of the catalytic process.

Q. 6

Q10 in enzyme matches with ‑

 A

2

 B

4

 C

8

 D

10

Q. 6

Q10 in enzyme matches with ‑

 A

2

 B

4

 C

8

 D

10

Ans. A

Explanation:

Ans. is ‘a’ i.e., 2

  • Most enzyme show a 50-300% (average 200%) increase in reaction rate when the temperature is increased by 10°, and the ratio of rate constant at two temperatures 10° apart is usually between 1.5 to 4 (average 2) for most enzymes.
  • This value is termed as Q10.
  • “The rate of enzymatic reaction doubles with every 10° rise in temperature. “

Q. 7

Fastest acting enzyme ‑

 A

LDH

 B

Trypsin

 C

Catalase

 D

None

Q. 7

Fastest acting enzyme ‑

 A

LDH

 B

Trypsin

 C

Catalase

 D

None

Ans. C

Explanation:

Ans. is ‘c’ i.e., Catalase 

Measurement of enzyme activity

  • The activity of enzyme is measured in terms of the following :
  • Unit of enzyme activity : – By international agreement, one unit enzyme activity is defined as the amount causing transformation of 1.0 micro mole of substrate per minute at 25° C. It is usually expressed as mole of substrate disappeared or mole of product formed per minute.
  • Specific activity : – It refers to the number of enzyme units per milligram of protein. It is a measure of enzyme purity; higher the enzyme purity, more is the specific activity.
  • Turn over number : – This refers to the number of substrate molecules transformed per unit time by a single enzyme molecule (or by a single catalytic site), when the enzyme concentration alone is rate-limiting factor. Catalase has the highest turnover number and hence is the fastest active enzyme. Carbonic anydrase has the 2″ fastest turnover number; therefore, it is 2nd fastest active enzyme (after catalase). Lysozyme has the lowest turnover number and therefore is slowest acting.

Quiz In Between



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