NEET-PG 2012

1213 Questions — Page 34 of 122

Biochemistry

4 questions

Q331

Which of the following fatty acids has the maximum number of carbon atoms?

Q332

What is the coenzyme form of pyridoxine?

Q333

What is the role of adenine phosphoribosyl transferase (APRT) in purine metabolism?

Q334

Which of the following does not play a role in protein synthesis?

NEET-PG 2012 - Biochemistry NEET-PG Practice Questions and MCQs

Question 331: Which of the following fatty acids has the maximum number of carbon atoms?

A. Oleic acid
B. Linolenic acid
C. Arachidonic acid
D. Cervonic acid (Correct Answer)

Explanation: **Cervonic acid** - **Cervonic acid**, also known as **docosahexaenoic acid (DHA)**, is a long-chain omega-3 fatty acid with **22 carbon atoms** and 6 double bonds (22:6). - It is a primary structural component of the brain and retina and is the longest fatty acid among the options provided. *Oleic acid* - **Oleic acid** is a monounsaturated fatty acid with **18 carbon atoms** and one double bond (18:1). - It is a common fatty acid found in many animal fats and vegetable oils, but it has fewer carbon atoms than cervonic acid. *Linolenic acid* - **Linolenic acid** refers to two essential fatty acids: alpha-linolenic acid (ALA) and gamma-linolenic acid (GLA). Both have **18 carbon atoms**. - Alpha-linolenic acid (ALA) is an omega-3 fatty acid with 3 double bonds (18:3), while gamma-linolenic acid (GLA) is an omega-6 fatty acid with 3 double bonds (18:3), neither of which has more carbon atoms than cervonic acid. *Arachidonic acid* - **Arachidonic acid** is an omega-6 fatty acid with **20 carbon atoms** and four double bonds (20:4). - It is a precursor to eicosanoids and is longer than oleic and linolenic acids but shorter than cervonic acid.

Question 332: What is the coenzyme form of pyridoxine?

A. ADP
B. NAD
C. PLP (Correct Answer)
D. FAD

Explanation: ***PLP*** - **Pyridoxal phosphate (PLP)** is the active coenzyme form of **pyridoxine (vitamin B6)**. - It plays a crucial role in numerous metabolic reactions, particularly those involving **amino acid metabolism**. *ADP* - **Adenosine diphosphate (ADP)** is an important molecule in energy transfer, particularly in the formation of **ATP (adenosine triphosphate)**. - It is not a coenzyme form of any vitamin, but rather a **nucleotide**. *NAD* - **Nicotinamide adenine dinucleotide (NAD)** is a coenzyme derived from **niacin (vitamin B3)**. - It functions as an electron carrier in **redox reactions** and is vital for cellular respiration. *FAD* - **Flavin adenine dinucleotide (FAD)** is a coenzyme derived from **riboflavin (vitamin B2)**. - It also serves as an electron carrier in **redox reactions**, particularly in the electron transport chain.

Question 333: What is the role of adenine phosphoribosyl transferase (APRT) in purine metabolism?

A. Breakdown of purines
B. Salvage pathway of purine nucleotide synthesis (Correct Answer)
C. Not involved in purine metabolism
D. De novo synthesis of purines

Explanation: ***Salvage pathway of purine nucleotide synthesis*** - **Adenine phosphoribosyl transferase (APRT)** catalyzes the reaction of **adenine** with **5-phosphoribosyl-1-pyrophosphate (PRPP)** to form **adenosine monophosphate (AMP)**. - This reaction is a crucial step in the **purine salvage pathway**, which reclaims pre-formed purine bases and converts them back into nucleotides, conserving energy. *Breakdown of purines* - The breakdown of purines (catabolism) typically involves enzymes like **adenosine deaminase** and **xanthine oxidase**, leading to the formation of **uric acid**. - APRT is involved in synthesizing nucleotides, not their degradation. *Not involved in purine metabolism* - APRT is an enzyme specifically involved in the **anabolic processes** of purine metabolism, as it contributes to the formation of purine nucleotides. - Its role is well-established within the **salvage pathway**. *De novo synthesis of purines* - The **de novo synthesis pathway** builds purine nucleotides from simpler precursors like **amino acids**, **CO2**, and **THF derivatives**. - While both pathways produce purine nucleotides, APRT is exclusively part of the **salvage pathway**, which recycles existing purine bases.

Question 334: Which of the following does not play a role in protein synthesis?

A. m-RNA
B. ATP
C. Intron (Correct Answer)
D. Exon

Explanation: ***Intron*** - Introns are **non-coding regions** within a gene that are transcribed into RNA but are subsequently **spliced out** before translation. - They do not carry genetic information for protein synthesis; their removal ensures the correct sequence of amino acids is produced. *Exon* - Exons are the **coding regions** of a gene that contain the genetic information for protein synthesis. - After introns are removed, exons are ligated together to form the **mature mRNA** that is translated into protein. *m-RNA* - **Messenger RNA (mRNA)** carries the genetic code from DNA in the nucleus to the ribosomes in the cytoplasm. - It serves as the **template** for protein synthesis through the process of translation. *ATP* - **Adenosine triphosphate (ATP)** provides the **energy** required for various steps in protein synthesis, including mRNA transcription, amino acid activation, and ribosome movement. - It is a crucial energy currency that fuels the process of forming peptide bonds and assembling the polypeptide chain.

Internal Medicine

3 questions

Q331

Which components of cigarette smoke are known to contribute to coronary artery disease?

Q332

What is the most common site of gastrointestinal stromal tumors (GISTs)?

Q333

Which of the following conditions is the classic example of acute intravascular hemolysis triggered by oxidative stress?

NEET-PG 2012 - Internal Medicine NEET-PG Practice Questions and MCQs

Question 331: Which components of cigarette smoke are known to contribute to coronary artery disease?

A. Nicotine, carbon monoxide, and tar (Correct Answer)
B. Carbon monoxide and tar
C. Carbon dioxide
D. Tar and nicotine

Explanation: ***Nicotine, carbon monoxide, and tar*** - **Nicotine** directly affects the cardiovascular system by increasing **heart rate**, **blood pressure**, and causing **vasoconstriction**, as well as promoting atherogenesis [2]. - **Carbon monoxide** binds to hemoglobin with higher affinity than oxygen, forming **carboxyhemoglobin**, which reduces oxygen delivery to tissues, leading to **endothelial damage** and contributing to atherosclerosis [1]. - **Tar** contains various **carcinogens** and toxic chemicals that contribute to inflammation, oxidative stress, and lipid peroxidation, all of which are implicated in the development and progression of **atherosclerosis**. *Carbon monoxide and tar* - While both contribute significantly, this option **omits nicotine**, which is a major contributor to the cardiovascular effects of smoking. - Nicotine's direct impact on **vasoconstriction** and **atherogenesis** is a critical factor in coronary artery disease [2]. *Carbon dioxide* - **Carbon dioxide** is a product of respiration and combustion but is not considered a primary direct contributor to the pathogenesis of **coronary artery disease** from cigarette smoke in the same way as nicotine, carbon monoxide, and tar. - Its presence in smoke primarily relates to its role in **respiratory physiology** rather than direct vascular damage. *Tar and nicotine* - This option correctly identifies **tar** and **nicotine** as contributors but **omits carbon monoxide**, which plays a crucial role in reducing oxygen-carrying capacity and directly damaging the endothelium [1]. - The impact of **carbon monoxide** on cardiac oxygen supply is a significant mechanism in smoking-related cardiovascular disease [1].

Question 332: What is the most common site of gastrointestinal stromal tumors (GISTs)?

A. Ileum
B. Esophagus
C. Colon
D. Stomach (Correct Answer)

Explanation: Stomach - The stomach is the most common site for gastrointestinal stromal tumors (GISTs), accounting for approximately 60-70% of cases. - GISTs in the stomach often present with symptoms like abdominal pain or bleeding and are associated with mutations in the KIT gene. Ileum - Although GISTs can occur in the ileum, they are far less common than those found in the stomach, representing about 10-15% of cases [1]. - GISTs in the ileum tend to present differently, often with intestinal obstruction or pain [1]. Esophagus - Esophageal GISTs are rare and account for only about 5% of GIST cases, making them an uncommon location. - Symptoms are usually related to dysphagia or chest pain, not typical for GISTs arising from more common sites. Colon - Although GISTs can occur in the colon, their frequency is much lower compared to the stomach and represents a small percentage of cases. - Clinical features in colonic GISTs can mimic other colorectal tumors, often causing obstruction or bleeding rather than classic GIST symptoms.

Question 333: Which of the following conditions is the classic example of acute intravascular hemolysis triggered by oxidative stress?

A. Hereditary spherocytosis
B. Sickle cell disease
C. Acute G6PD deficiency (Correct Answer)
D. None of the options

Explanation: ***b and c*** - Intravascular hemolysis is commonly associated with both **Acute G6PD deficiency** and **Hereditary spherocytosis**, leading to destruction of red blood cells in the bloodstream [1]. - These conditions are characterized by **high levels of hemoglobinuria** and **low haptoglobin**, indicative of intravascular hemolysis. *Sickle cell ds* - Sickle cell disease primarily causes **extravascular hemolysis** due to splenic sequestration rather than **intravascular** destruction [3]. - The clinical features include **vaso-occlusive crises** and splenic infarction rather than hemolysis within the blood vessels. *Acute G6PD* - While acute G6PD deficiency can lead to hemolysis, it is typically **triggered by oxidative stress** rather than occurring continuously [2]. - The hemolysis in G6PD deficiency occurs more in an **extravascular** manner unless acute stress occurs, which can result in **acute intravascular hemolysis, marked by anemia, hemoglobinemia, and hemoglobinuria** [4]. *Hereditary spherocytosis* - This condition primarily causes **extravascular hemolysis** through the spleen, where abnormal spherocytes are destroyed [1]. - Although it leads to anemia, the hallmark of hereditary spherocytosis is the **spleen's role** in hemocyte destruction rather than intravascular hemolysis.

Pathology

1 questions

Q331

Helmet cells are characteristic of anemia of?

Physiology

2 questions

Q331

Gastric secretions are essential for absorption of -

Q332

What happens to the concentration of inulin as fluid passes through the Proximal Convoluted Tubule (PCT)?

NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs

Question 331: Gastric secretions are essential for absorption of -

A. Cobalamin (Correct Answer)
B. Fat
C. Thiamine
D. Folic acid

Explanation: ***Cobalamin*** - **Intrinsic factor**, secreted by gastric parietal cells, is crucial for the absorption of **vitamin B12 (cobalamin)** in the terminal ileum [1]. - Without sufficient intrinsic factor, **pernicious anemia** can develop due to impaired B12 absorption [2]. *Fat* - Fat digestion primarily occurs in the **small intestine** with the help of **bile salts** and **pancreatic lipases**. - While gastric lipase begins some fat digestion, it's not essential for overall fat absorption. *Thiamine* - **Thiamine (vitamin B1)** is absorbed in the jejunum and ileum, primarily via **active transport** and passive diffusion. - Gastric secretions do not play a direct, essential role in its absorption. *Folic acid* - **Folic acid** is absorbed in the **duodenum and jejunum** as monoglutamates after being deconjugated from polyglutamate forms. - This process is not directly dependent on gastric secretions [2].

Question 332: What happens to the concentration of inulin as fluid passes through the Proximal Convoluted Tubule (PCT)?

A. Concentration of inulin increases (Correct Answer)
B. Concentration of urea remains constant
C. Concentration of HCO3- increases
D. Concentration of Na+ decreases

Explanation: ***Concentration of inulin increases*** - Inulin is **freely filtered** at the glomerulus and is neither reabsorbed nor secreted along the renal tubule, making it an excellent marker for **glomerular filtration rate (GFR)**. - As water is reabsorbed from the PCT, the volume of tubular fluid decreases, causing the concentration of **unreabsorbed solutes**, like inulin, to increase. *Concentration of urea remains constant* - Urea is **reabsorbed** along the tubule, though passively; its concentration typically **increases** initially in the PCT due to water reabsorption, but then decreases as some is reabsorbed. - The statement is incorrect because urea concentration changes significantly throughout the nephron, particularly increasing as water is reabsorbed and then decreasing with some reabsorption. *Concentration of HCO3- increases* - The majority (approximately 80-90%) of **bicarbonate (HCO3-)** is reabsorbed in the PCT, primarily through its conversion to CO2 within the tubular lumen and then back to HCO3- intracellularly. - Therefore, the concentration of HCO3- in the tubular fluid actually **decreases** significantly as fluid passes through the PCT. *Concentration of Na+ decreases* - **Sodium (Na+)** is actively reabsorbed along the entire nephron, with about 65-70% reabsorbed in the PCT. - While Na+ is reabsorbed, water follows passively, so its concentration in the tubular fluid remains relatively **iso-osmotic** with plasma, meaning its concentration does not significantly decrease as fluid passes through the PCT, remaining fairly constant.