NEET-PG 2015 - Biochemistry Practice Questions

Q: Which of the following statements about NADP is correct?

Involved in HMP shunt. ***Involved in HMP shunt*** - **NADPH**, the reduced form of NADP+, is primarily generated in the **hexose monophosphate shunt (HMP shunt)**, specifically during the oxidative phase. - The NADPH produced in the HMP shunt is crucial for **reductive biosynthesis** reactions and maintaining the **redox balance** of the cell. *Acts as a coenzyme form of Riboflavin* - **NADP is derived from Niacin (Vitamin B3)**, not Riboflavin (Vitamin B2). - **Flavin adenine dinucleotide (FAD)** and **flavin mononucleotide (FMN)** are the coenzyme forms of Riboflavin. *Involved in glycolysis* - **NADP is not directly involved in glycolysis**; instead, **NAD+** is the primary coenzyme that accepts electrons in glycolysis, specifically during the oxidation of glyceraldehyde-3-phosphate. - While some enzymes in glycolysis can interact with NADP+ under specific conditions, its main role is not within the glycolytic pathway. *Involved in fatty acid oxidation* - **Fatty acid oxidation (beta-oxidation)** primarily utilizes **NAD+** and **FAD** as electron acceptors. - **NADP+** is not a direct participant in the electron transport chain during fatty acid breakdown.

Q: Level of which of the following is not elevated in heart disease

5-nucleotidase. ***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.

Q: Enzyme activity is expressed as?

Micromoles/min. ***Micromoles/min*** - Enzyme activity is typically measured by the rate at which an enzyme converts its **substrate into product**. - This rate is often expressed as the amount of product formed (e.g., **micromoles**) or substrate consumed per unit of time (e.g., **per minute**). *Millimoles/lit* - This unit expresses **concentration** (moles per liter) rather than a rate of reaction. - While enzyme reactions involve changes in substrate/product concentration, this unit alone does not describe the **activity or catalytic speed** of the enzyme. *Milli gm/lit* - This unit also expresses **concentration by mass** (milligrams per liter), not enzyme activity. - It does not account for the **time-dependent nature** of enzyme catalysis or the molar quantity of reactants/products. *Mg/dl* - This unit represents **concentration by mass** (milligrams per deciliter), commonly used for measuring substances like glucose or cholesterol in blood. - It is not appropriate for expressing the **catalytic rate or activity** of an enzyme.

Q: Which of the following statements about adiponectin is incorrect?

Positive Correlation with BMI. ***Positive Correlation with BMI (INCORRECT STATEMENT)*** - Adiponectin levels are **inversely correlated with BMI**, NOT positively correlated; as BMI increases, adiponectin levels generally decrease. - This inverse relationship is significant because lower adiponectin levels are associated with increased insulin resistance and **metabolic syndrome**. - This statement is **false**, making it the correct answer to this question. *Secreted by adipose tissue (Correct statement)* - Adiponectin is a **hormone primarily secreted by adipocytes** (fat cells). - It plays a crucial role in regulating glucose and lipid metabolism, and its secretion is altered in conditions like obesity. - This statement is **true**. *Lowers glucose (Correct statement)* - Adiponectin **enhances insulin sensitivity** in peripheral tissues like skeletal muscle and liver, leading to increased glucose uptake and utilization. - This action helps to **lower blood glucose levels** and improve glycemic control. - This statement is **true**. *Increases FFA oxidation (Correct statement)* - Adiponectin **promotes fatty acid oxidation** in muscle and liver, reducing intracellular lipid accumulation. - By increasing fatty acid burning, it helps to **decrease circulating free fatty acid (FFA) levels**, which can contribute to insulin resistance if elevated. - This statement is **true**.

Q: Location of gene on chromosome is identified by

Genetic mapping. ***Genetic mapping*** - **Genetic mapping** (also called chromosome mapping) uses various techniques to determine the **physical location (locus)** of genes on a chromosome. - Techniques include **linkage analysis**, **FISH (Fluorescence In Situ Hybridization)**, chromosomal banding, and analysis of **inheritance patterns** of traits and genetic markers. - This identifies both the **relative positions** between genes and their **absolute chromosomal addresses**. *Karyotyping* - **Karyotyping** is a technique that visualizes the entire set of chromosomes in an organism. - While it can identify **large chromosomal abnormalities** like aneuploidy or major deletions/insertions, it does not pinpoint the exact location of a specific gene. *Microarray* - **Microarray** technology is used to study the expression levels of thousands of genes simultaneously or to detect specific genetic variations. - It does not directly map the physical location of a gene on a chromosome. *Genomic imprinting* - **Genomic imprinting** is an epigenetic phenomenon where certain genes are expressed in a **parent-of-origin-specific manner**. - It describes a mechanism of gene regulation rather than a method for identifying the location of a gene on a chromosome.

Q: What is the primary receptor for High-Density Lipoprotein (HDL) in cholesterol metabolism?

SR-BI. ***SR-BI*** - **Scavenger Receptor class B type 1 (SR-BI)** is the primary receptor responsible for selective uptake of **cholesteryl esters** from HDL into cells, particularly the liver and steroidogenic tissues. - Unlike other lipoprotein receptors, SR-BI mediates the **selective transfer** of cholesterol without internalizing the entire HDL particle. *LDLR* - The **Low-Density Lipoprotein Receptor (LDLR)** is the primary receptor for **LDL** and very low-density lipoprotein (VLDL) remnants, mediating their endocytosis and degradation. - While it plays a crucial role in cholesterol metabolism, its main function is related to the uptake of **LDL cholesterol**, not HDL. *HDLR* - **HDLR** is not a recognized receptor in cholesterol metabolism. - This term may be a distracter created by combining HDL with the common receptor nomenclature. *SR-82* - **SR-82** is not a recognized receptor involved in cholesterol metabolism. - Similar to HDLR, this is a distracter term.

Q: Most important carbohydrate store for maintaining blood glucose homeostasis -

Hepatic glycogen. ***Hepatic glycogen*** - The liver contains **100-120g of glycogen**, which is the most crucial carbohydrate store for **maintaining blood glucose homeostasis**. - **Hepatic glycogen** can be mobilized and released as glucose into the bloodstream to supply all body tissues, especially during fasting. - Although muscle glycogen is quantitatively larger (~400-500g), it cannot contribute to blood glucose as muscle lacks glucose-6-phosphatase. - The liver's unique ability to release free glucose makes hepatic glycogen the **most metabolically important** carbohydrate store. *Blood glucose* - **Blood glucose** (~5g total in circulation) represents carbohydrates available for immediate energy, not a storage form. - This is far too small to be considered a major carbohydrate reserve. *Glycogen in adipose tissue* - **Adipose tissue** primarily stores **fat (triglycerides)**, with negligible glycogen content. - Adipose tissue plays virtually no role in carbohydrate storage. *None of the options* - This is incorrect because **hepatic glycogen** is indeed the most important carbohydrate store for glucose homeostasis.

Q: Which of the following is NOT a function of glycosaminoglycans?

Transport of lipids in the bloodstream. ***Transport of lipids in the bloodstream*** - Glycosaminoglycans (GAGs) generally do not play a direct role in the **transport of lipids** in the bloodstream. Lipid transport is primarily mediated by **lipoproteins** (e.g., chylomicrons, VLDL, LDL, HDL). - While some GAGs might interact with lipoproteins in the extracellular matrix, their fundamental role is not lipid transport but rather structural and signaling functions. *Lubrication of joints* - This is a well-established function of GAGs, particularly **hyaluronic acid**, which contributes to the **viscoelastic properties of synovial fluid**, reducing friction in joints. - Hyaluronic acid helps maintain the **hydration** and **shock-absorbing capacity** of articular cartilage. *Wound healing process* - Glycosaminoglycans, especially **hyaluronic acid** and **heparin sulfate**, are crucial in **wound healing** processes, where they modulate inflammation, cell migration, and tissue remodeling. - They provide a **scaffold for cell proliferation** and differentiation in the wound bed. *Anticoagulant activity* - **Heparin**, a highly sulfated glycosaminoglycan, is a potent **anticoagulant** that works by activating **antithrombin III**, thereby inhibiting various coagulation factors like thrombin. - Other GAGs, like **heparan sulfate** found on cell surfaces, also exhibit mild anticoagulant properties.

Q: C4, C5, and N7 in the purine ring are derived from which of the following?

Glycine. ***Glycine*** - The entire **glycine molecule** contributes C4, C5, and N7 to the purine ring structure. - This amino acid provides a significant portion of the backbone to the imidazole ring within the purine. *Aspartate* - **Aspartate** contributes N1 to the purine ring. - It does not involve C4, C5, or N7, which are distinct atoms within the purine molecule. *CO₂* - **CO₂** contributes C6 to the purine ring through a carboxylation step. - It is not involved in providing the atoms at positions C4, C5, or N7. *Glutamine* - The nitrogen atoms N3 and N9 in the purine ring are derived from the **amide nitrogen of glutamine**. - Glutamine's contributions are different from the carbons and nitrogen provided by glycine.

Q: Which gene is responsible for the production of COX type 3?

COX I gene. ***COX I gene*** - COX-3 is an **alternatively spliced variant** of the **COX-1 gene** (specifically, a splice variant of the COX-1 mRNA that retains intron 1). - While it was initially thought to be a distinct gene, research has shown that it arises from the same genetic locus as COX-1. *COX 2 gene* - The COX-2 gene encodes for the **inducible cyclooxygenase enzyme**, which is responsible for prostaglandin synthesis during inflammation. - It is a separate gene from COX-1 and has distinct regulatory mechanisms and physiological roles. *COX 3 gene* - There is currently **no distinct gene in humans** specifically identified as "COX-3". - COX-3 refers to a protein isoform derived from the COX-1 gene, not a separate genetic locus. *None of the above* - This option is incorrect because COX-3 is indeed derived from the **COX-1 gene** through alternative splicing. - The existence of COX-3 as a distinct protein product has been demonstrated, although its precise physiological role in humans is still under investigation.

Question 1

Which of the following statements about NADP is correct?

Accepted Answer

Involved in HMP shunt

Answer

Involved in fatty acid oxidation

Answer

Involved in glycolysis

Answer

Acts as a coenzyme form of Riboflavin

Question 2

Level of which of the following is not elevated in heart disease

Accepted Answer

5-nucleotidase

Answer

SGOT

Answer

ALP

Answer

LDH

Question 3

Enzyme activity is expressed as?

Accepted Answer

Micromoles/min

Answer

Millimoles/lit

Answer

Milli gm/lit

Answer

Mg/dl

Question 4

Which of the following statements about adiponectin is incorrect?

Accepted Answer

Positive Correlation with BMI

Answer

Secreted by adipose tissue

Answer

Increases FFA oxidation

Answer

Lowers glucose

Question 5

Location of gene on chromosome is identified by

Accepted Answer

Genetic mapping

Answer

Karyotyping

Answer

Microarray

Answer

Genomic imprinting

Question 6

What is the primary receptor for High-Density Lipoprotein (HDL) in cholesterol metabolism?

Accepted Answer

SR-BI

Answer

LDLR

Answer

HDLR

Answer

SR-82

Question 7

Most important carbohydrate store for maintaining blood glucose homeostasis -

Accepted Answer

Hepatic glycogen

Answer

Blood glucose

Answer

Glycogen in adipose tissue

Answer

None of the options

Question 8

Which of the following is NOT a function of glycosaminoglycans?

Accepted Answer

Transport of lipids in the bloodstream

Answer

Lubrication of joints

Answer

Wound healing process

Answer

Anticoagulant activity

Question 9

C4, C5, and N7 in the purine ring are derived from which of the following?

Accepted Answer

Glycine

Answer

CO₂

Answer

Aspartate

Answer

Glutamine

Question 10

Which gene is responsible for the production of COX type 3?

Accepted Answer

COX I gene

Answer

COX 3 gene

Answer

COX 2 gene

Answer

None of the above

NEET-PG 2015 — Biochemistry