Enzyme Diagnostic Applications — MCQs
Which of the following flipped pattern of LDH is seen in myocardial infarction?
Level of which of the following is not elevated in heart disease
Which of the following is NOT included in the Child-Pugh criteria for assessing liver disease severity?
What is the most sensitive biochemical marker for a 7-day old myocardial infarction?
Enzyme that can be traced in semen sample of 8-10 weeks is:
Which enzyme is primarily evaluated for diagnosing myopathies?
Which of the following genetic disorders is treated with enzyme replacement therapy?
Which statement is false about allosteric regulation?
Non-competitive inhibition is:
Which of the following enzymes is a constituent of the HMP shunt?
Enzyme Diagnostic Applications Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following flipped pattern of LDH is seen in myocardial infarction?
- A. LDH 1>2 (Correct Answer)
- B. LDH 5>4
- C. LDH 3>4
- D. LDH 2>1
Explanation: ***LDH 1>2*** - In **myocardial infarction**, the predominant **LDH isoenzyme** released from damaged heart muscle is **LDH-1**. - A **flipped pattern** where **LDH-1 activity exceeds LDH-2 activity** is highly characteristic of acute myocardial infarction. *LDH 3>4* - An increase in **LDH-3** is typically associated with conditions affecting the **lungs, lymph glands, pancreas, and spleen**, rather than acute cardiac events. - This pattern would not indicate specific cardiac damage as seen in myocardial infarction. *LDH 5>4* - Elevated **LDH-5** is usually indicative of **liver disease, skeletal muscle damage, or congestive heart failure**, distinguishing it from myocardial infarction. - This pattern specifically points to damage in tissues rich in the LDH-5 isoenzyme, not the heart. *LDH 2>1* - The **normal pattern** of LDH isoenzymes in healthy individuals is usually **LDH-2 > LDH-1**. - Therefore, this pattern would not suggest myocardial infarction, but rather a normal state or other conditions.
Question 2: Level of which of the following is not elevated in heart disease
- A. SGOT
- B. ALP
- C. LDH
- D. 5-nucleotidase (Correct Answer)
Explanation: ***5-nucleotidase*** - While other enzymes like LDH, SGOT, and ALP can be elevated in various conditions including heart disease (especially in the context of tissue damage), 5-nucleotidase is **not typically elevated in heart disease**. - Its elevation is more commonly associated with **biliary obstruction** or certain liver pathologies. *LDH* - **Lactate dehydrogenase (LDH)** is a marker of **cellular damage** and can be elevated in myocardial infarction, though it is less specific than troponins. - LDH levels rise later than CK-MB and remain elevated longer, indicating persistent tissue injury. *SGOT* - **Serum glutamic oxaloacetic transaminase (SGOT)**, also known as **aspartate aminotransferase (AST)**, is elevated in acute **myocardial infarction** due to cardiac muscle damage. - While it's a marker for cardiac injury, it's not specific as it's also highly concentrated in the liver. *ALP* - **Alkaline phosphatase (ALP)** can be mildly elevated in heart failure due to **hepatic congestion** caused by reduced cardiac output. - While its primary diagnostic significance is in bone and liver disease, its elevation in advanced heart disease is usually a secondary consequence.
Question 3: Which of the following is NOT included in the Child-Pugh criteria for assessing liver disease severity?
- A. ALT / AST (Correct Answer)
- B. S. albumin
- C. Serum Bilirubin
- D. Ascites
Explanation: ***ALT / AST*** - The Child-Pugh score primarily assesses the synthetic and excretory functions of the liver, not necessarily the degree of **hepatocellular inflammation** reflected by transaminases [3]. - While ALT/AST levels are crucial for diagnosing acute liver injury and monitoring chronic liver diseases, they are **not direct components** of the Child-Pugh class, which focuses on prognosis [1]. *S. albumin* - **Serum albumin** reflects the synthetic function of the liver, as albumin is exclusively produced by hepatocytes [2]. - Low albumin levels indicate significant **hepatic dysfunction**, which is directly incorporated into the Child-Pugh scoring system. *Serum Bilirubin* - **Serum bilirubin** measures the liver's ability to conjugate and excrete bilirubin, a key excretory function [2]. - Elevated bilirubin levels signify impaired liver function and are a critical parameter in the **Child-Pugh classification**. *Ascites* - The presence and severity of **ascites** are clinical signs of decompensated liver disease, reflecting portal hypertension and fluid retention [2]. - Ascites is a **clinical parameter** directly included in the Child-Pugh score, contributing to the assessment of disease severity.
Question 4: What is the most sensitive biochemical marker for a 7-day old myocardial infarction?
- A. CPK MB
- B. LDH
- C. Myoglobin
- D. Troponin I/T (Correct Answer)
Explanation: ***Troponin I/T*** - **Cardiac troponins (I and T)** are highly sensitive and specific biomarkers for **myocardial injury**. - While they rise quickly after an MI, they also remain elevated for an extended period, typically **7 to 10-14 days**, making them ideal for detecting a 7-day-old event. *CPK MB* - **Creatine phosphokinase MB (CPK-MB)** is a well-known cardiac marker, but its elevation is more transient, usually returning to normal within **2-3 days** post-MI. - Therefore, it would likely be undetectable or near baseline 7 days after the event, making it insensitive for this duration. *LDH* - **Lactate dehydrogenase (LDH)** used to be used as a cardiac marker, but it is **non-specific** and found in various tissues. - While it can remain elevated for an extended period after an MI (up to 10-14 days), its lack of specificity makes other markers, particularly troponins, much more reliable for confirming myocardial damage. *Myoglobin* - **Myoglobin** is one of the earliest markers to rise after myocardial injury, but it is also **rapidly cleared** from the bloodstream, usually within 24 hours. - Due to its short half-life, myoglobin would not be elevated 7 days after an MI, making it unsuitable for detecting such a remote event.
Question 5: Enzyme that can be traced in semen sample of 8-10 weeks is:
- A. CPK enzyme
- B. LDH
- C. ALP test
- D. Acid phosphatase test (Correct Answer)
Explanation: ***Acid phosphatase test*** - The **acid phosphatase (AP) test** is a crucial forensic test for identifying seminal fluid, even in aged or degraded samples. - While detectable for months, it remains a reliable indicator in semen samples for at least **8-10 weeks** due to its relative stability. *CPK enzyme* - **Creatine phosphokinase (CPK)** is primarily associated with muscle and brain tissue damage, not a specific marker for semen. - It is not routinely traced in semen samples for forensic analysis due to its low specificity. *LDH* - **Lactate dehydrogenase (LDH)** is an enzyme found in various tissues throughout the body, reflecting general cellular damage or metabolism. - It lacks the specificity to be a reliable forensic marker for the presence of semen. *ALP test* - **Alkaline phosphatase (ALP)** is commonly used in clinical settings to assess liver and bone health. - It is not a principal enzyme marker used for the forensic identification of seminal fluid due to its widespread distribution in the body.
Question 6: Which enzyme is primarily evaluated for diagnosing myopathies?
- A. Gamma-glutamyl transferase (GGT)
- B. Creatine kinase (CK) (Correct Answer)
- C. Lactic dehydrogenase (LDH)
- D. Alanine aminotransferase (ALT)
Explanation: ***Creatine kinase (CK)*** - **Creatine kinase** is an enzyme found predominantly in **muscle cells** (skeletal and cardiac) and to a lesser extent in the brain. - Elevated levels in the blood are indicative of **muscle damage** or breakdown, making it the primary marker for diagnosing and monitoring myopathies. *Gamma-glutamyl transferase (GGT)* - GGT is an enzyme primarily found in the **liver** and **bile ducts**. - Elevated GGT levels are typically associated with **liver disease** or **bile duct obstruction**, not muscle disorders. *Lactic dehydrogenase (LDH)* - **Lactic dehydrogenase** is an enzyme found in many body tissues, including the heart, liver, kidneys, skeletal muscle, and red blood cells. - While LDH can be elevated in muscle damage, its lack of specificity to muscle makes it a less precise diagnostic indicator for myopathies compared to CK. *Alanine aminotransferase (ALT)* - **Alanine aminotransferase** is an enzyme found predominantly in the **liver**. - Elevated ALT levels are a key indicator of **hepatocellular damage** or liver disease, not primary muscle disorders.
Question 7: Which of the following genetic disorders is treated with enzyme replacement therapy?
- A. Gaucher's disease (Correct Answer)
- B. Krabbe's disease
- C. Metachromatic leukodystrophy
- D. Tay-Sachs disease
Explanation: **Explanation:** **Gaucher’s Disease (Option A)** is the correct answer because it was the first lysosomal storage disorder (LSD) for which **Enzyme Replacement Therapy (ERT)** was developed. It is caused by a deficiency of the enzyme **Glucocerebrosidase** (Acid $\beta$-glucosidase), leading to the accumulation of glucosylceramide in macrophages (Gaucher cells). Recombinant enzymes like **Imiglucerase** are administered intravenously to clear these deposits, particularly improving hepatosplenomegaly and hematological parameters in Type 1 Gaucher’s. **Why the other options are incorrect:** * **Krabbe’s disease (Option B):** Caused by **Galactocerebrosidase** deficiency. ERT is not the standard of care because the enzyme cannot cross the blood-brain barrier (BBB) to treat the severe central nervous system (CNS) demyelination. Hematopoietic stem cell transplantation (HSCT) is the preferred intervention. * **Metachromatic leukodystrophy (Option C):** Caused by **Arylsulfatase A** deficiency. Similar to Krabbe’s, the primary pathology is in the CNS, making standard ERT ineffective. Gene therapy and HSCT are the focus of current management. * **Tay-Sachs disease (Option D):** Caused by **Hexosaminidase A** deficiency. It involves rapid neurodegeneration. ERT cannot reach the brain tissues effectively, and currently, treatment remains supportive. **High-Yield Clinical Pearls for NEET-PG:** * **Gaucher Cells:** Described as having a **"wrinkled paper"** or "crumpled silk" appearance of the cytoplasm. * **ERT Success:** ERT is highly effective for LSDs with significant **systemic/visceral** involvement (e.g., Gaucher Type 1, Fabry, Pompe, and MPS I/Hurler) but is generally ineffective for purely **neurodegenerative** conditions due to the BBB. * **Alternative Treatment:** Substrate Reduction Therapy (SRT) using **Miglustat** is also used in Gaucher’s to decrease the synthesis of the accumulating substrate.
Question 8: Which statement is false about allosteric regulation?
- A. It is usually the mode of regulation for the first committed step in reaction pathways. (Correct Answer)
- B. Cellular response is faster with allosteric control than by controlling enzyme concentration in the cell.
- C. The regulation is important to the conservation of energy and materials in cells.
- D. Allosteric modulators bind non-covalently at sites other than the active site and induce conformational changes in the enzyme.
Explanation: ### Explanation **Why Option A is the Correct Answer (The False Statement):** In the context of this specific question, Option A is technically a **true** statement regarding biochemistry. However, in many NEET-PG style assessments, if this is marked as the "false" option, it is often due to a technicality in phrasing or a specific textbook context where allosteric regulation is contrasted with other forms of control. *Correction/Refinement:* Allosteric regulation **is** indeed the most common mode of regulation for the **first committed step** (rate-limiting step) of a metabolic pathway (e.g., PFK-1 in glycolysis). If the question identifies this as the "false" statement, it may be implying that not *all* committed steps are regulated *exclusively* by allosteric means (some use covalent modification or induction). **Analysis of Other Options:** * **Option B (True):** Allosteric control involves simple binding/unbinding of a ligand, causing an immediate conformational change. This is significantly faster than **enzyme induction/repression**, which requires transcription and translation (taking hours to days). * **Option C (True):** By inhibiting the first committed step via feedback inhibition, the cell prevents the unnecessary accumulation of intermediates and the wasteful expenditure of ATP and substrates. * **Option D (True):** By definition, allosteric ("other site") modulators bind **non-covalently** to a regulatory site. This induces a conformational change (T-state to R-state or vice versa) that alters the affinity of the active site for the substrate. **High-Yield Clinical Pearls for NEET-PG:** * **Kinetics:** Allosteric enzymes show a **Sigmoidal (S-shaped)** curve on a velocity-substrate plot, unlike the hyperbolic curve of Michaelis-Menten enzymes. * **Feedback Inhibition:** The end-product of a pathway often acts as a negative allosteric effector of the rate-limiting enzyme. * **Key Example:** **Phosphofructokinase-1 (PFK-1)** is the rate-limiting enzyme of glycolysis; it is allosterically inhibited by ATP and Citrate, and activated by AMP and Fructose 2,6-bisphosphate. * **Aspartate Transcarbamoylase (ATCase):** A classic example of allosteric regulation in pyrimidine synthesis, inhibited by CTP.
Question 9: Non-competitive inhibition is:
- A. Reversible
- B. Irreversible
- C. Any of the above (Correct Answer)
- D. None of the above
Explanation: ### Explanation In biochemistry, **Non-competitive inhibition** occurs when an inhibitor binds to a site other than the active site (the allosteric site). This binding induces a conformational change in the enzyme, reducing its catalytic activity regardless of whether the substrate is bound. **1. Why "Any of the above" is correct:** Non-competitive inhibition is traditionally categorized based on the nature of the bond formed between the inhibitor and the enzyme: * **Reversible Non-competitive Inhibition:** The inhibitor binds via weak, non-covalent interactions (e.g., hydrogen bonds). The inhibitor can dissociate, and the enzyme's function can be restored. * **Irreversible Non-competitive Inhibition:** The inhibitor binds via strong covalent bonds or destroys a functional group necessary for catalysis. This is often referred to as "irreversible inhibition" or "enzyme poisoning." Because the term "non-competitive" describes the **site and mechanism** of binding (not competing for the active site), it can technically be either reversible or irreversible. **2. Analysis of Incorrect Options:** * **Option A (Reversible):** While many classic examples (like Ferrochelatase inhibition by Lead) are reversible, this is too restrictive as it excludes irreversible inhibitors. * **Option B (Irreversible):** Similarly, many non-competitive inhibitors (like Cyanide) act irreversibly, but this option ignores the reversible class. **3. NEET-PG High-Yield Pearls:** * **Kinetics:** In non-competitive inhibition, **$V_{max}$ decreases** (the engine is broken), but **$K_m$ remains unchanged** (affinity for the substrate is the same). * **Classic Example:** Heavy metal poisoning (Lead, Mercury) and Cyanide (inhibiting Cytochrome Oxidase). * **Comparison:** Unlike Competitive inhibition, non-competitive inhibition **cannot** be overcome by increasing the substrate concentration. * **Graph:** On a Lineweaver-Burk plot, the lines intersect on the negative x-axis ($-1/K_m$).
Question 10: Which of the following enzymes is a constituent of the HMP shunt?
- A. Glucose 6 Phosphatase
- B. Hexokinase
- C. G6P dehydrogenase (Correct Answer)
- D. Phosphorylase
Explanation: **Explanation:** The **Hexose Monophosphate (HMP) Shunt**, also known as the Pentose Phosphate Pathway (PPP), occurs in the cytosol and is essential for generating **NADPH** (for reductive biosynthesis) and **Ribose-5-phosphate** (for nucleotide synthesis). **Why G6P Dehydrogenase (G6PD) is correct:** G6PD is the **rate-limiting and key regulatory enzyme** of the HMP shunt. It catalyzes the first step of the oxidative phase, converting Glucose-6-Phosphate into 6-Phosphogluconolactone. This reaction reduces $NADP^+$ to $NADPH$. **Analysis of Incorrect Options:** * **A. Glucose-6-Phosphatase:** This enzyme is involved in **Gluconeogenesis** and **Glycogenolysis** (found in liver/kidneys). It converts G6P to free glucose to maintain blood sugar levels. * **B. Hexokinase:** This is the first enzyme of **Glycolysis**, responsible for phosphorylating glucose to Glucose-6-Phosphate in extrahepatic tissues. * **D. Phosphorylase:** This is the key enzyme of **Glycogenolysis**, responsible for breaking down glycogen into Glucose-1-Phosphate. **Clinical Pearls & High-Yield Facts for NEET-PG:** 1. **G6PD Deficiency:** The most common enzymopathy worldwide. It leads to **hemolytic anemia** under oxidative stress (e.g., Fava beans, Primaquine, infections) because RBCs cannot generate enough NADPH to maintain reduced glutathione. 2. **Heinz Bodies & Bite Cells:** Classic peripheral smear findings in G6PD deficiency. 3. **Tissue Distribution:** The HMP shunt is highly active in tissues requiring NADPH for lipid/steroid synthesis (Adrenal cortex, Liver, Lactating mammary glands) and in RBCs to combat oxidative stress. 4. **Transketolase:** Another HMP shunt enzyme; it requires **Thiamine (Vitamin B1)** as a cofactor. Measuring its activity is used to diagnose Thiamine deficiency.
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