Anatomy
1 questionsWhich of these best describes the renal angle?
NEET-PG 2012 - Anatomy NEET-PG Practice Questions and MCQs
Question 251: Which of these best describes the renal angle?
- A. The angle between the latissimus dorsi and the 12th rib
- B. The angle between the erector spinae and the iliac crest
- C. The angle between the 12th rib and the erector spinae (Correct Answer)
- D. The angle between the 12th rib and the rectus abdominis
Explanation: ***The angle between the 12th rib and the erector spinae*** - The **renal angle** (also known as the costovertebral angle) is the space formed by the junction of the **12th rib** and the **erector spinae muscles** laterally. - This anatomical landmark is clinically significant for assessing **kidney pain** or inflammation (e.g., in pyelonephritis) through percussion. *The angle between the latissimus dorsi and the 12th rib* - While the **latissimus dorsi** is a significant back muscle, it is not the primary anatomical landmark that defines the renal angle. - The renal angle specifically refers to the relationship between the rib cage and the deeper spinal muscles. *The angle between the erector spinae and the iliac crest* - This description refers to a region lower down on the back, closer to the **pelvis**, and not directly related to the position of the kidneys. - The **iliac crest** defines the upper border of the pelvis, far from the kidney's typical location relative to the 12th rib. *The angle between the 12th rib and the rectus abdominis* - The **rectus abdominis** muscle is located on the anterior (front) aspect of the abdomen, involved in trunk flexion. - This muscle is anatomically distinct and separate from the posterior flank region where the kidneys are located and where the renal angle is assessed.
Biochemistry
7 questionsEnzyme deficient in Type I Hyperlipidemia?
What is the primary biochemical defect in alkaptonuria?
Which one of the following statements concerning gluconeogenesis is correct?
Which of the following best describes the difference between glucokinase and hexokinase?
In the context of cell membrane composition, what is the typical weight ratio of protein to lipid?
Type of inhibition of aconitase by trans-aconitate is?
In ETC NADH generates -
NEET-PG 2012 - Biochemistry NEET-PG Practice Questions and MCQs
Question 251: Enzyme deficient in Type I Hyperlipidemia?
- A. HMG CoA reductase
- B. Lipoprotein lipase (Correct Answer)
- C. Peroxidase
- D. Cholesterol acyl transferase
Explanation: ***Lipoprotein lipase*** - **Type I hyperlipidemia**, also known as **familial hyperchylomicronemia**, is characterized by a deficiency in **lipoprotein lipase (LPL)**. - LPL is crucial for hydrolyzing triglycerides in **chylomicrons** and **VLDLs** into fatty acids and glycerol, allowing their uptake by tissues. *HMG CoA reductase* - This enzyme is involved in the **rate-limiting step of cholesterol synthesis** in the liver. - While it plays a role in lipid metabolism, its deficiency is not characteristic of **Type I hyperlipidemia**. *Peroxidase* - **Peroxidase** is an enzyme involved in various oxidative reactions, including the breakdown of **hydrogen peroxide**. - It is not directly involved in the metabolism of **chylomicrons** or **triglycerides**, and its deficiency is unrelated to hyperlipidemia. *Cholesterol acyl transferase* - This enzyme, often referring to **lecithin-cholesterol acyltransferase (LCAT)** or **acyl-CoA:cholesterol acyltransferase (ACAT)**, is involved in **cholesterol esterification**. - While important for cholesterol transport and storage, its deficiency is not the primary cause of **Type I hyperlipidemia**, which is marked by severe **chylomicronemia**.
Question 252: What is the primary biochemical defect in alkaptonuria?
- A. FeCl3 test is negative
- B. Urine turns black immediately upon voiding
- C. Benedict's test is diagnostic for alkaptonuria
- D. Deficiency of homogentisate 1,2-dioxygenase (Correct Answer)
Explanation: ***Deficiency of homogentisate 1,2-dioxygenase*** - **Alkaptonuria** is an autosomal recessive disorder caused by the deficiency of **homogentisate 1,2-dioxygenase**, an enzyme in the **tyrosine degradation pathway**. - This deficiency leads to the accumulation of **homogentisic acid** in the body, which is excreted in urine and deposited in connective tissues. *Urine turns black immediately upon voiding* - While urine in alkaptonuria does **turn black**, it typically darkens upon **standing** and exposure to air, not immediately upon voiding. - The darkening is due to the oxidation of accumulated **homogentisic acid**. *FeCl3 test is negative* - The **ferric chloride (FeCl3) test** typically yields a **positive result** (transient green color) in the presence of homogentisic acid in the urine. - Therefore, a negative result would argue against a diagnosis of alkaptonuria. *Benedict's test is diagnostic for alkaptonuria* - **Benedict's test** is used to detect reducing sugars like glucose in urine and would not be used to diagnose alkaptonuria. - A positive Benedict's test in alkaptonuria is due to the reducing properties of homogentisic acid, but it is not specific or diagnostic.
Question 253: Which one of the following statements concerning gluconeogenesis is correct?
- A. It occurs primarily in the liver.
- B. It is stimulated by elevated levels of acetyl CoA.
- C. It is important in maintaining blood glucose during the normal overnight fast. (Correct Answer)
- D. It is primarily inhibited by insulin.
Explanation: ***It is important in maintaining blood glucose during the normal overnight fast.*** - **This is the BEST answer** as it emphasizes the **primary physiological role** of gluconeogenesis in human metabolism. - During the **overnight fast** (8-12 hours), hepatic glycogen stores become depleted, making gluconeogenesis the **critical mechanism** to maintain blood glucose for glucose-dependent tissues like the **brain** (requires ~120g glucose/day) and **red blood cells**. - Without gluconeogenesis, blood glucose would drop dangerously during fasting, leading to hypoglycemia and neurological dysfunction. *It occurs primarily in the liver.* - This statement is **technically correct** - the liver accounts for approximately **90%** of total gluconeogenesis under normal conditions. - However, the **kidney cortex** also contributes significantly (10% normally, up to 40% during prolonged fasting), and the **intestine** plays a minor role. - While true, this is more of a **anatomical fact** rather than highlighting the critical physiological importance of the pathway, making it a less comprehensive answer than Option 1. *It is stimulated by elevated levels of acetyl CoA.* - This statement is **biochemically correct** - **Acetyl-CoA** is an important **allosteric activator** of **pyruvate carboxylase**, the first committed enzyme of gluconeogenesis. - However, this represents just **one regulatory mechanism** at the enzymatic level, not the overall physiological significance. - Primary regulation occurs through **hormones** (glucagon, cortisol, epinephrine) that coordinate the entire pathway, making this a narrower answer than Option 1. *It is primarily inhibited by insulin.* - This statement is also **correct** - **Insulin** is the primary hormonal **inhibitor** of gluconeogenesis. - Insulin suppresses gluconeogenesis by inhibiting key enzymes (PEPCK, glucose-6-phosphatase) and decreasing transcription of gluconeogenic genes. - However, this describes **inhibition** rather than the positive physiological role, making it less representative of gluconeogenesis's essential function than Option 1. **Note:** All four statements are technically correct, but Option 1 best captures the **essential physiological importance** of gluconeogenesis in human metabolism, which is why it is the preferred answer for this question.
Question 254: Which of the following best describes the difference between glucokinase and hexokinase?
- A. Glucokinase has higher Km for glucose compared to hexokinase. (Correct Answer)
- B. Glucokinase is not inhibited by glucose-6-phosphate unlike hexokinase.
- C. Glucokinase has a low affinity for glucose.
- D. Glucokinase activity increases with glucose concentration while hexokinase remains saturated.
Explanation: ***Glucokinase has higher Km for glucose compared to hexokinase*** - **Glucokinase** has a **Km of ~10 mM** for glucose, while **hexokinase** has a **Km of ~0.1 mM**, making glucokinase's Km approximately **100-fold higher** - This **high Km** is the fundamental biochemical parameter that defines glucokinase's unique role as a **glucose sensor** in liver and pancreatic β-cells - The high Km means glucokinase activity is **proportional to blood glucose concentration** in the physiological range (5-15 mM), allowing it to regulate glucose metabolism in response to feeding - This is the **most precise biochemical descriptor** of the difference, from which other functional characteristics derive *Glucokinase has a low affinity for glucose* - While this statement is **correct** (high Km = low affinity), it is a **qualitative description** of what Km quantifies - Option stating "higher Km" is more specific and biochemically precise than simply stating "low affinity" *Glucokinase is not inhibited by glucose-6-phosphate unlike hexokinase* - This is a **correct and important regulatory difference** - **Hexokinase** is allosterically inhibited by its product **glucose-6-phosphate**, providing feedback regulation to prevent excessive glucose phosphorylation when cellular needs are met - **Glucokinase** lacks this product inhibition, allowing the liver to continue glucose uptake and storage even when G6P levels are high after meals - However, this describes a regulatory difference rather than the fundamental kinetic parameter *Glucokinase activity increases with glucose concentration while hexokinase remains saturated* - This statement is **correct** and describes the **functional consequence** of the different Km values - **Hexokinase** with its low Km (~0.1 mM) is saturated at normal blood glucose levels (5 mM), operating at Vmax - **Glucokinase** with its high Km (~10 mM) shows increasing activity as glucose rises from 5 to 15 mM postprandially - This is a physiological consequence rather than the fundamental biochemical parameter
Question 255: In the context of cell membrane composition, what is the typical weight ratio of protein to lipid?
- A. 1 : 2
- B. 4 : 1
- C. 1 : 1 (Correct Answer)
- D. 2 : 1
Explanation: ***1 : 1*** - The **typical weight ratio of protein to lipid** in most cell membranes is approximately **1:1** (equal by weight). - While the **number of lipid molecules** far exceeds the number of protein molecules, proteins are much larger and heavier, resulting in roughly equal weight contributions. - This **1:1 ratio represents an average** for typical plasma membranes, though it can vary significantly depending on membrane type and function. *1 : 2* - This protein:lipid ratio would indicate **lipids contribute twice as much by weight** as proteins. - This is characteristic of **myelin membranes**, which are specialized for insulation and have exceptionally high lipid content. - However, this is **not typical** of most cell membranes. *2 : 1* - This ratio would suggest **proteins contribute twice as much by weight** as lipids. - While some protein-rich membranes exist, this is **higher than the average** for typical cell membranes. - The typical ratio is closer to 1:1 rather than being protein-dominant at 2:1. *4 : 1* - A 4:1 protein:lipid ratio represents an **extremely protein-rich membrane**. - This is characteristic of the **inner mitochondrial membrane**, which is packed with electron transport chain proteins. - This is a **specialized membrane**, not representative of typical cell membranes.
Question 256: Type of inhibition of aconitase by trans-aconitate is?
- A. Competitive (Correct Answer)
- B. Non-competitive
- C. Allosteric
- D. None of the options
Explanation: ***Competitive*** - **Competitive inhibition** occurs when the inhibitor (trans-aconitate) structurally resembles the enzyme's natural substrate (cis-aconitate) and binds to the **active site**, preventing the substrate from binding. - This type of inhibition can be overcome by increasing the concentration of the **substrate**. *Non-competitive* - **Non-competitive inhibitors** bind to a site on the enzyme other than the active site, causing a conformational change that reduces the enzyme's efficiency, regardless of substrate concentration. - Trans-aconitate's structural similarity to aconitate's substrate points away from a non-competitive mechanism. *Allosteric* - **Allosteric inhibition** involves an inhibitor binding to a regulatory site (allosteric site) on the enzyme, which is distinct from the active site, to alter enzyme activity. - While allosteric regulation is a type of non-competitive inhibition, trans-aconitate's direct structural resemblance to the substrate makes competitive inhibition the more specific and accurate description. *None of the options* - This option is incorrect because **competitive inhibition** accurately describes the mechanism by which trans-aconitate inhibits aconitase, given its structural similarity to the natural substrate. - The other options are less fitting due to the specific characteristics of trans-aconitate's action.
Question 257: In ETC NADH generates -
- A. 1 ATPs
- B. 4 ATPs
- C. 3 ATPs (Correct Answer)
- D. 2 ATPs
Explanation: ***3 ATPs*** - Each molecule of **NADH** donates electrons to **Complex I** of the electron transport chain (ETC), resulting in the pumping of enough protons to generate approximately **3 ATP molecules** via **oxidative phosphorylation**. - This high yield is due to NADH's ability to activate multiple proton pumps along the ETC, maximizing the **proton gradient** for ATP synthesis. *1 ATPs* - This is an incorrect yield for NADH; **FADH2** typically generates fewer ATPs (around 2) because it enters the ETC at a later stage, bypassing the initial proton pump. - Generating only 1 ATP from NADH would be very inefficient and is not physiologically accurate for oxidative phosphorylation. *2 ATPs* - While closer, 2 ATPs is the approximate yield for **FADH2**, which enters the ETC at **Complex II**, bypassing Complex I and thus pumping fewer protons. - NADH enters at Complex I, which provides enough energy for a higher ATP yield. *4 ATPs* - 4 ATPs is an overestimation of the ATP yield from NADH in the electron transport chain. - The maximum theoretical yield from NADH via oxidative phosphorylation is typically considered to be 3 ATPs.
Physiology
2 questionsOsmolarity is defined as?
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 251: Osmolarity is defined as?
- A. Number of osmoles per litre (Correct Answer)
- B. Number of osmoles per kg
- C. Weight of solute per litre of solution
- D. Weight of solvent per litre of solution
Explanation: ***Number of osmoles per litre*** - **Osmolarity** is a measure of the **solute concentration** in a solution, specifically the number of **osmoles of solute per liter of solution**. - It is often used in clinical settings to assess the **concentration of dissolved particles** in bodily fluids like plasma. *Number of osmoles per kg* - This definition describes **osmolality**, which measures the concentration of a solution as the **number of osmoles of solute per kilogram of solvent**. - While related, osmolarity and osmolality are distinct terms, with osmolality being less affected by temperature and pressure changes. *Weight of solute per litre of solution* - This definition describes a **mass concentration** (e.g., g/L), but it does not account for the **number of osmotically active particles**. - Different solutes can have the same weight but varying numbers of particles (e.g., 1 mol of glucose vs. 1 mol of NaCl dissociates into 2 particles). *Weight of solvent per litre of solution* - This statement incorrectly relates to solvent quantity rather than solute concentration and is not a standard definition for osmolarity or any related osmotic property. - The focus of osmolarity is on the concentration of the **dissolved particles (solute)**, not the weight of the solvent.
Question 252: 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.