Enzymes Practice Questions

Q: Serum alkaline phosphatase levels increase in which of the following conditions?

Hyperparathyroidism. **Explanation:** **Alkaline Phosphatase (ALP)** is a group of isoenzymes that catalyze the hydrolysis of organic phosphates at an alkaline pH. It is primarily found in the **liver** (biliary canaliculi) and **bone** (osteoblasts). **Why Hyperparathyroidism is correct:** In hyperparathyroidism, elevated Parathyroid Hormone (PTH) stimulates osteoclastic bone resorption. However, this is coupled with compensatory **osteoblastic activity** to repair the bone. Since ALP is a marker of osteoblastic activity, its serum levels rise significantly in conditions involving high bone turnover, such as Hyperparathyroidism, Paget’s disease, and Rickets/Osteomalacia. **Analysis of Incorrect Options:** * **Hypothyroidism:** This is associated with **decreased** ALP levels due to reduced bone turnover and metabolism. (Other causes of low ALP include Hypophosphatasia and Zinc deficiency). * **Carcinoma of the Prostate:** While this can cause elevated ALP if it metastasizes to the bone (osteoblastic metastases), the classic marker for prostate cancer is **Acid Phosphatase (ACP)** and Prostate-Specific Antigen (PSA). * **Myocardial Infarction:** The primary markers for MI are Troponins, CK-MB, and LDH-1. ALP has no significant presence in cardiac muscle. **High-Yield Clinical Pearls for NEET-PG:** * **Physiological Increase:** Seen in growing children (bone growth) and the 3rd trimester of pregnancy (placental isoenzyme). * **Heat Stability:** To differentiate the source of ALP, remember: *"Regan is Heat Stable"* (Placental/Cancer isoenzymes are heat-stable, while Bone ALP is heat-labile). * **Biliary Marker:** ALP is the most sensitive marker for **obstructive jaundice** (cholestasis).

Q: In myocardial infarction, which enzyme is typically elevated within 4 to 6 hours and returns to normal levels in 3 to 4 days?

CK-MB (CPK). **Explanation:** The correct answer is **CK-MB (CPK)**. In the context of Myocardial Infarction (MI), cardiac biomarkers follow a specific temporal pattern of rise, peak, and decline, which is high-yield for NEET-PG. **1. Why CK-MB is correct:** CK-MB (Creatine Kinase-MB) is a relatively specific isoenzyme for cardiac muscle. Following myocardial injury, it begins to rise within **4 to 6 hours**, reaches its peak at 18 to 24 hours, and typically returns to baseline within **48 to 72 hours (2 to 3 days)**. Because of its rapid clearance, it is the gold-standard marker for detecting **re-infarction** occurring shortly after the initial event. **2. Why other options are incorrect:** * **AST (SGOT):** It rises within 8–12 hours and returns to normal in 4–5 days. It is less specific than CK-MB as it is also found in the liver and skeletal muscle. * **LDH (Lactate Dehydrogenase):** This is a late marker. It begins to rise after 24 hours, peaks at 3–6 days, and remains elevated for **8–14 days**. It is useful for late diagnosis of MI. * **ALT (SGPT):** Primarily a marker for hepatocellular injury; it has minimal diagnostic value for MI. **3. Clinical Pearls for NEET-PG:** * **Troponin I & T:** These are the most sensitive and specific markers for MI. They rise within 3–4 hours but remain elevated for **7–10 days (Troponin I)** or **up to 14 days (Troponin T)**. * **Myoglobin:** The **earliest** marker to rise (within 1–3 hours), but it lacks specificity as it is also present in skeletal muscle. * **Order of appearance:** Myoglobin > CK-MB/Troponins > AST > LDH.

Q: An 10-month-old baby presents with diarrhea, hair loss, and failure to thrive. Clinical examination reveals inflammation of the skin around the mouth and perianal region. Which mineral deficiency is responsible for this condition, acting as a cofactor for all the following enzymes EXCEPT?

Glutathione peroxidase. **Explanation:** The clinical presentation described—diarrhea, alopecia (hair loss), and periorificial dermatitis (inflammation around the mouth and anus)—is the classic triad of **Acrodermatitis Enteropathica**. This condition is caused by a deficiency of **Zinc**, either due to an autosomal recessive mutation in the ZIP4 transporter or acquired nutritional deficiency. **Why Glutathione Peroxidase is the correct answer:** Zinc serves as a vital cofactor for over 300 enzymes. However, **Glutathione peroxidase** is a **Selenium-dependent** enzyme. It contains selenocysteine at its active site and functions to protect cells from oxidative damage by reducing lipid hydroperoxides. Since Zinc is not its cofactor, it is the correct "EXCEPT" choice. **Analysis of Incorrect Options (Zinc-dependent enzymes):** * **Lactate dehydrogenase (LDH):** A zinc-containing metalloenzyme essential for anaerobic glycolysis, converting pyruvate to lactate. * **Alcohol dehydrogenase:** This enzyme requires Zinc to maintain its structural integrity and catalytic activity during the metabolism of ethanol to acetaldehyde. * **Alkaline phosphatase (ALP):** A key marker of bone and liver metabolism; it is a Zinc-dependent enzyme. In fact, low serum ALP levels can sometimes be a diagnostic clue for Zinc deficiency. **High-Yield NEET-PG Pearls:** * **Zinc Finger Motifs:** Zinc is essential for DNA-binding proteins (transcription factors) and steroid hormone receptors. * **Wound Healing:** Zinc is a cofactor for **collagenase**, making it crucial for tissue repair. * **Other Zinc enzymes:** Carbonic anhydrase, Carboxypeptidase, and RNA/DNA polymerases. * **Clinical Sign:** Hypogeusia (loss of taste) and impaired night vision (Zinc is needed for Retinol dehydrogenase) are common early signs of deficiency.

Q: Which biochemical marker is most specific for alcoholic liver disease?

GGT (Gamma-Glutamyl Transferase). **Explanation:** **Gamma-Glutamyl Transferase (GGT)** is the most sensitive and specific biochemical marker for alcoholic liver disease. The primary reason is that alcohol acts as a potent **enzyme inducer** of GGT in the hepatocytes. Even in the absence of significant liver cell damage, chronic alcohol consumption leads to elevated GGT levels. Furthermore, GGT is particularly useful in distinguishing whether an elevated Alkaline Phosphatase (ALP) is of hepatic or bony origin, as GGT is not found in bone. **Analysis of Incorrect Options:** * **AST (Aspartate Aminotransferase):** While AST is typically higher than ALT in alcoholic hepatitis (the classic **AST:ALT ratio > 2:1**), AST is not specific to the liver; it is also found in cardiac muscle, skeletal muscle, and RBCs. * **ALT (Alanine Aminotransferase):** ALT is more specific to the liver than AST, but it is often **low or normal** in alcoholic liver disease because alcoholics are frequently deficient in **Pyridoxal-5-phosphate (Vitamin B6)**, a necessary co-factor for ALT synthesis. * **ALP (Alkaline Phosphatase):** This is a marker of cholestasis or bone turnover. While it may rise in alcoholic cirrhosis, it lacks the specificity for alcohol induction seen with GGT. **High-Yield Clinical Pearls for NEET-PG:** * **AST:ALT Ratio:** A ratio > 2:1 is highly suggestive of alcoholic liver disease ("**S**" in AST stands for "**S**cotch"). * **Isolated GGT elevation:** Often the first sign of occult alcohol abuse in an otherwise asymptomatic patient. * **MCV Connection:** In chronic alcoholics, elevated GGT is often accompanied by an **increased Mean Corpuscular Volume (Macrocytosis)** due to direct bone marrow toxicity or folate deficiency.

Q: What type of enzyme is Ribonuclease-P?

Ribozyme. **Explanation:** **Why Ribozyme is Correct:** Ribonuclease-P (RNase P) is a unique enzyme because its catalytic activity is mediated by an **RNA molecule** rather than a protein. Enzymes composed of ribonucleic acid are termed **Ribozymes**. RNase P is an endoribonuclease responsible for the processing of precursor tRNA (pre-tRNA) by cleaving the 5' extra sequence to generate mature tRNA. While it exists as a ribonucleoprotein complex, the RNA component alone is capable of catalysis in the presence of magnesium ions. **Why Other Options are Incorrect:** * **A. Ligase:** These enzymes catalyze the joining of two molecules (e.g., DNA ligase) using ATP. RNase P performs cleavage, not ligation. * **B. Lyase:** These enzymes catalyze the breaking of various chemical bonds by means other than hydrolysis and oxidation, often forming a new double bond. RNase P specifically utilizes a hydrolytic mechanism. * **C. Hydrolase:** While RNase P chemically functions as a phosphodiesterase (a type of hydrolase), the question asks for the *type* of enzyme based on its composition. In the context of NEET-PG, RNase P is the classic example of a Ribozyme. **High-Yield Clinical Pearls for NEET-PG:** * **Other Ribozymes to remember:** Peptidyl transferase (23S rRNA in prokaryotes/28S rRNA in eukaryotes), SnRNAs (involved in splicing), and self-splicing introns. * **Nobel Prize Connection:** Sidney Altman and Thomas Cech were awarded the Nobel Prize for the discovery of the catalytic properties of RNA. * **Function:** RNase P is essential in all three domains of life for the maturation of tRNA.

Q: Which of the following statements is FALSE regarding Cytochrome P-450 enzymes?

They are non-heme proteins.. ### Explanation **1. Why Option D is the Correct Answer (The False Statement)** Cytochrome P450 (CYP) enzymes are **heme-containing proteins** (hemeproteins). They belong to a superfamily of enzymes that contain a molecule of iron-protoporphyrin IX at their active site. This heme group is essential for their function as it binds oxygen and facilitates the hydroxylation of various substrates. Therefore, stating they are "non-heme proteins" is biochemically incorrect. **2. Analysis of Incorrect Options (True Statements)** * **Option A:** CYPs are crucial for the **biosynthesis of steroid hormones** (e.g., cortisol, aldosterone, and sex steroids) in the adrenal cortex and gonads, as well as the synthesis of bile acids and Vitamin D. * **Option B:** The name "P450" is derived from the fact that when these enzymes are in a reduced state and bound to carbon monoxide (CO), they exhibit a characteristic absorption peak (Soret peak) at **450 nm**. * **Option C:** These enzymes are primarily located in the **smooth endoplasmic reticulum** (microsomes) of hepatocytes, where they play a central role in the Phase I metabolism (hydroxylation) of drugs and xenobiotics. **3. Clinical Pearls & High-Yield Facts for NEET-PG** * **Reaction Type:** They are **Monooxygenases** (Mixed-function oxidases). They incorporate one atom of oxygen into the substrate and reduce the other atom to water. * **Requirement:** They require **NADPH** and the enzyme **NADPH-cytochrome P450 reductase**. * **Inducers vs. Inhibitors:** * *Inducers:* Rifampicin, Phenytoin, Carbamazepine, Chronic Alcohol (increase drug metabolism). * *Inhibitors:* Ketoconazole, Erythromycin, Cimetidine, Grapefruit juice (decrease drug metabolism, leading to toxicity). * **Polymorphism:** CYP2D6 shows significant genetic polymorphism, affecting the metabolism of drugs like codeine and beta-blockers.

Q: Which of the following is an example of a metalloenzyme?

Lysyl oxidase. **Explanation:** The distinction between a **metalloenzyme** and a **metal-activated enzyme** is a high-yield concept in Biochemistry. A metalloenzyme contains a tightly bound metal ion as an integral part of its structure, which is essential for its catalytic activity. **1. Why Lysyl Oxidase is Correct:** Lysyl oxidase is a classic example of a **metalloenzyme** that requires **Copper (Cu²⁺)** as a cofactor. It plays a critical role in the extracellular matrix by catalyzing the oxidative deamination of lysine and hydroxylysine residues in collagen and elastin. This process leads to the formation of allysine, which is necessary for the **cross-linking** of collagen fibers, providing tensile strength to tissues. **2. Analysis of Incorrect Options:** * **Lysyl hydroxylase & Prolyl hydroxylase:** These enzymes are involved in the post-translational modification of collagen *inside* the cell. They are not metalloenzymes in the same category; they require **Ferrous iron (Fe²⁺)** and **Vitamin C (Ascorbic acid)** as cofactors. Deficiency leads to Scurvy. * **Glucosyl transferase:** This enzyme is involved in the glycosylation of hydroxylysine residues during collagen synthesis and does not function as a copper-dependent metalloenzyme. **3. High-Yield Clinical Pearls for NEET-PG:** * **Menkes Disease:** A defect in copper absorption (ATP7A gene) leads to low copper levels, causing decreased **Lysyl oxidase** activity. This results in "kinky hair," connective tissue defects, and arterial tortuosity. * **Wilson Disease:** A defect in copper excretion (ATP7B gene) leading to copper toxicity. * **Other Copper-containing enzymes:** Tyrosinase, Cytochrome c oxidase, Superoxide dismutase (cytosolic), and Ceruloplasmin. * **Zinc-containing enzymes:** Carbonic anhydrase, Alcohol dehydrogenase, and Carboxypeptidase.

Q: Glutathione peroxidase is a/an?

Antioxidant. **Explanation:** **Glutathione Peroxidase (GPx)** is a critical intracellular enzyme that functions as a major **antioxidant**. Its primary role is to protect cells from oxidative damage by catalyzing the reduction of hydrogen peroxide ($H_2O_2$) and lipid hydroperoxides into water and alcohols, respectively. This reaction uses **Reduced Glutathione (GSH)** as a hydrogen donor, converting it into its oxidized form (GSSG). **Why Option B is Correct:** GPx is the body’s primary defense against oxidative stress in the cytosol and mitochondria. By neutralizing reactive oxygen species (ROS), it prevents lipid peroxidation of cell membranes and DNA damage. **Analysis of Incorrect Options:** * **Option A (Catalase):** While both GPx and Catalase decompose $H_2O_2$, they are distinct enzymes. Catalase is primarily located in **peroxisomes** and handles high concentrations of $H_2O_2$, whereas GPx is found in the cytosol and mitochondria and is effective even at low peroxide concentrations. * **Option C (Microsomal enzyme):** Microsomal enzymes (like the Cytochrome P450 system) are located in the smooth endoplasmic reticulum and are mainly involved in drug metabolism (xenobiotics). GPx is not a microsomal enzyme. **High-Yield Clinical Pearls for NEET-PG:** * **Selenium Dependency:** GPx is a **selenoprotein**; it contains the 21st amino acid, **Selenocysteine**, at its active site. Selenium deficiency leads to reduced GPx activity. * **G6PD Link:** The regeneration of GSH (required by GPx) depends on **Glutathione Reductase**, which requires **NADPH**. This NADPH is supplied by the HMP Shunt (G6PD enzyme). This is why G6PD deficiency leads to hemolysis due to oxidative stress. * **Location:** It is the most abundant selenoprotein in mammals, found in almost all tissues.

Question 1

Serum alkaline phosphatase levels increase in which of the following conditions?

Accepted Answer

Hyperparathyroidism

Answer

Hypothyroidism

Answer

Carcinoma of the prostate

Answer

Myocardial infarction

Question 2

In myocardial infarction, which enzyme is typically elevated within 4 to 6 hours and returns to normal levels in 3 to 4 days?

Accepted Answer

CK-MB (CPK)

Answer

AST (SGOT)

Answer

LDH

Answer

ALT (SGPT)

Question 3

Which one of the following statements about Km value is true?

Accepted Answer

Km is independent of enzyme concentration.

Answer

Km is the substrate concentration at which the reaction velocity is half of the maximal velocity.

Answer

A lower numerical value of Km indicates a higher affinity of the enzyme for its substrate.

Answer

Km denotes the substrate concentration at which 100% of enzyme molecules are saturated with substrate molecules.

Question 4

An 10-month-old baby presents with diarrhea, hair loss, and failure to thrive. Clinical examination reveals inflammation of the skin around the mouth and perianal region. Which mineral deficiency is responsible for this condition, acting as a cofactor for all the following enzymes EXCEPT?

Accepted Answer

Glutathione peroxidase

Answer

Lactate dehydrogenase

Answer

Alcohol dehydrogenase

Answer

Alkaline phosphatase

Question 5

Which biochemical marker is most specific for alcoholic liver disease?

Accepted Answer

GGT (Gamma-Glutamyl Transferase)

Answer

AST (Aspartate Aminotransferase)

Answer

ALT (Alanine Aminotransferase)

Answer

ALP (Alkaline Phosphatase)

Question 6

What type of enzyme is Ribonuclease-P?

Accepted Answer

Ribozyme

Answer

Ligase

Answer

Lyase

Answer

Hydrolase

Question 7

Which of the following enzymes is NOT responsible for the removal of free radicals?

Accepted Answer

NADPH oxidase

Answer

Catalase

Answer

Superoxide Dismutase

Answer

Glutathione peroxidase

Question 8

Which of the following statements is FALSE regarding Cytochrome P-450 enzymes?

Accepted Answer

They are non-heme proteins.

Answer

They are involved in the production of steroids.

Answer

They absorb maximum light at 450nm wavelength.

Answer

They are present in the endoplasmic reticulum of liver cells.

Question 9

Which of the following is an example of a metalloenzyme?

Accepted Answer

Lysyl oxidase

Answer

Lysyl hydroxylase

Answer

Prolyl hydroxylase

Answer

Glucosyl transferase

Question 10

Glutathione peroxidase is a/an?

Accepted Answer

Antioxidant

Answer

Catalase

Answer

Microsomal enzyme

Answer

None of the above

Enzymes — MCQs

Enzymes — MCQs

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