Anatomy
1 questionsNutrient artery runs ?
NEET-PG 2012 - Anatomy NEET-PG Practice Questions and MCQs
Question 171: Nutrient artery runs ?
- A. Away from epiphysis (Correct Answer)
- B. Towards metaphysis
- C. None of the options
- D. Away from metaphysis
Explanation: ***Away from epiphysis*** - The **nutrient artery** runs away from the **dominant (faster-growing) epiphysis** towards the non-dominant end of the bone. - This follows the classic anatomical rule: **"To the elbow, from the knee"** - nutrient arteries point towards the elbow in upper limb bones and away from the knee in lower limb bones. - The **nutrient foramen** is directed obliquely away from the more actively growing end, established during bone development. - Examples: In the humerus, it runs towards the elbow (away from proximal epiphysis); in the femur, it runs away from the knee (away from distal epiphysis). *Towards metaphysis* - While the artery does course towards the metaphyseal region of the slower-growing end, this option is less anatomically precise. - The standard teaching emphasizes the relationship with the **dominant epiphysis** rather than the metaphysis. *Away from metaphysis* - This is **incorrect** - the nutrient artery actually runs **towards** the metaphysis of the non-dominant end. - It runs **away from** the dominant epiphysis, not away from the metaphysis. *None of the options* - This is incorrect as **"Away from epiphysis"** correctly describes the direction of the nutrient artery relative to the dominant growing end.
Biochemistry
9 questionsWhich enzyme primarily initiates the electron transport process in oxidative phosphorylation?
What is the net number of ATP molecules and NADH formed in glycolysis per glucose molecule?
Which molecule serves as a key link between carbohydrate metabolism and fatty acid synthesis?
Which carbohydrate is primarily metabolized by Aldolase-B?
Which of the following statements about chylomicrons is true?
Which enzyme is primarily responsible for the fat metabolism in adipose tissue?
Which cofactor is primarily associated with the activity of glutamate dehydrogenase?
Which of the following metabolites is involved in glycogenolysis, glycolysis and gluconeogenesis ?
Which one of the following statements concerning gluconeogenesis is correct?
NEET-PG 2012 - Biochemistry NEET-PG Practice Questions and MCQs
Question 171: Which enzyme primarily initiates the electron transport process in oxidative phosphorylation?
- A. Pyruvate kinase
- B. Succinyl CoA thiokinase
- C. NADH dehydrogenase (Correct Answer)
- D. ATP synthase
Explanation: ***Correct NADH dehydrogenase*** - **NADH dehydrogenase**, also known as Complex I, is the enzyme that accepts electrons from **NADH** during oxidative phosphorylation, initiating the electron transport chain. - This enzyme **oxidizes NADH** to NAD+ and pumps protons from the mitochondrial matrix to the intermembrane space, contributing to the **proton gradient**. *Incorrect Pyruvate kinase* - **Pyruvate kinase** is an enzyme involved in **glycolysis**, catalyzing the final step of converting phosphoenolpyruvate to pyruvate. - It functions in the **cytoplasm** and is not directly involved in the electron transport chain or oxidative phosphorylation. *Incorrect Succinyl CoA thiokinase* - **Succinyl CoA thiokinase** (also known as succinate thiokinase or succinyl-CoA synthetase) is an enzyme in the **Krebs cycle** (citric acid cycle). - It catalyzes the reversible reaction of converting succinyl-CoA to succinate and is not directly part of the electron transport chain. *Incorrect ATP synthase* - **ATP synthase** (Complex V) is the enzyme responsible for synthesizing ATP using the **proton gradient** established by the electron transport chain. - While crucial for oxidative phosphorylation, it acts at the end of the process, utilizing the energy generated, rather than initiating electron transport.
Question 172: What is the net number of ATP molecules and NADH formed in glycolysis per glucose molecule?
- A. 4 ATP, 2 NADH
- B. 4 ATP, 4 NADH
- C. 2 ATP, 4 NADH
- D. 2 ATP, 2 NADH (Correct Answer)
Explanation: **2 ATP, 2 NADH** - Glycolysis has a net yield of **2 molecules of ATP** because 4 ATP molecules are produced, but 2 ATP molecules are consumed during the initial energy investment phase. - **2 molecules of NADH** are also produced during the energy generation phase when glyceraldehyde-3-phosphate is oxidized. *4 ATP, 2 NADH* - While 4 ATP molecules are indeed produced during glycolysis, this option does not account for the **2 ATP molecules consumed** in the initial steps, leading to an incorrect net value. - The production of **2 NADH** is correct, but the ATP count is the gross rather than the net. *4 ATP, 4 NADH* - This option overstates the production of both ATP and NADH. While **4 ATP are produced (gross)**, the net is 2 ATP. - Only **2 NADH** molecules are formed per glucose molecule in glycolysis, not 4. *2 ATP, 4 NADH* - This option accurately reflects the **net ATP yield of 2 molecules**. - However, it exaggerates the production of NADH, as only **2 molecules of NADH** are formed during glycolysis, not 4.
Question 173: Which molecule serves as a key link between carbohydrate metabolism and fatty acid synthesis?
- A. Glucose-6-phosphate
- B. Acetyl-CoA
- C. Citrate (Correct Answer)
- D. Succinyl-CoA
Explanation: ***Citrate*** - **Citrate** is the crucial molecule that links carbohydrate metabolism to fatty acid synthesis via the **citrate-malate shuttle** - In the fed state, excess **acetyl-CoA** (derived from glucose metabolism via glycolysis and pyruvate dehydrogenase) condenses with oxaloacetate to form citrate in the mitochondria - **Citrate** is then transported from mitochondria to the cytosol, where **ATP-citrate lyase** cleaves it to regenerate **acetyl-CoA** and **oxaloacetate** for fatty acid synthesis - This is the primary mechanism for transporting acetyl-CoA equivalents from mitochondria (where glucose is oxidized) to the cytosol (where fatty acids are synthesized) - Citrate also acts as an **allosteric activator** of **acetyl-CoA carboxylase**, the rate-limiting enzyme of fatty acid synthesis *Glucose-6-phosphate* - While **glucose-6-phosphate** is a key intermediate in glycolysis and gluconeogenesis, it is not the molecule that directly links carbohydrate breakdown to fatty acid synthesis - It is several steps removed from the generation of cytosolic acetyl-CoA needed for fatty acid synthesis *Acetyl-CoA* - **Acetyl-CoA** is the direct precursor for fatty acid synthesis - However, acetyl-CoA generated in mitochondria from glucose oxidation **cannot directly cross the mitochondrial membrane** - It must be transported as citrate, making citrate the actual linking molecule between the two compartments *Succinyl-CoA* - **Succinyl-CoA** is a Krebs cycle intermediate involved in heme synthesis and propionate metabolism - It is not involved in transporting acetyl units from mitochondria to cytosol for fatty acid synthesis
Question 174: Which carbohydrate is primarily metabolized by Aldolase-B?
- A. Galactose
- B. Fructose (Correct Answer)
- C. Sucrose
- D. None of the options
Explanation: ***Fructose*** - **Aldolase B** is a key enzyme in the liver responsible for the metabolism of **fructose**, specifically cleaving **fructose-1-phosphate** into **dihydroxyacetone phosphate** and **glyceraldehyde**. - A deficiency in **Aldolase B** leads to **hereditary fructose intolerance**, causing an accumulation of **fructose-1-phosphate** after fructose ingestion. *Galactose* - **Galactose** is primarily metabolized by enzymes in the **Leloir pathway**, including **galactokinase** and **galactose-1-phosphate uridylyltransferase**. - **Aldolase B** plays no significant role in the metabolism of galactose. *Sucrose* - **Sucrose** is a disaccharide composed of **glucose** and **fructose**. - It is first broken down by **sucrase** in the small intestine into its constituent monosaccharides before they are metabolized further. *None of the options* - This option is incorrect because **fructose** is indeed a carbohydrate primarily metabolized by Aldolase-B. - The enzyme's specific role in fructose metabolism is well-established.
Question 175: Which of the following statements about chylomicrons is true?
- A. Chylomicrons are unrelated to triglyceride transport.
- B. Chylomicrons primarily contain cholesterol.
- C. Chylomicrons primarily contain triglycerides (TGs). (Correct Answer)
- D. Chylomicrons do not primarily contain triglycerides.
Explanation: ***Chylomicrons primarily contain triglycerides (TGs)*** - **Chylomicrons** are the largest and least dense lipoproteins, primarily responsible for transporting **dietary triglycerides** absorbed from the intestine to peripheral tissues. - They are synthesized in the **enterocytes** of the small intestine and released into the lymphatic system. - Approximately **85-90%** of a chylomicron's mass is composed of **triglycerides**, making them the primary carriers of exogenous fats. *Chylomicrons primarily contain cholesterol* - While chylomicrons do contain some **cholesterol**, it is a minor component (~3-5%) compared to their predominant content, which is **triglycerides**. - Lipoproteins like **LDL** and **HDL** are primarily responsible for cholesterol transport. *Chylomicrons are unrelated to triglyceride transport* - This statement is incorrect; chylomicrons are fundamentally involved in the **transport of dietary triglycerides** from the intestines to various tissues in the body. - After lipoprotein lipase acts on chylomicrons in peripheral tissues, triglycerides are hydrolyzed and fatty acids are taken up by tissues. *Chylomicrons do not primarily contain triglycerides* - This statement directly contradicts the main function and composition of chylomicrons, which are **rich in triglycerides**. - Without triglycerides as their primary content, chylomicrons would not be able to fulfill their physiological role in lipid transport.
Question 176: Which enzyme is primarily responsible for the fat metabolism in adipose tissue?
- A. Lipoprotein lipase
- B. Hormone-sensitive lipase (Correct Answer)
- C. Acid lipase
- D. Acid maltase
Explanation: ***Hormone-sensitive lipase*** - This enzyme is crucial for the **mobilization of stored triglycerides** in adipose tissue by hydrolyzing them into fatty acids and glycerol. - Its activity is stimulated by hormones like **epinephrine** and **norepinephrine** and inhibited by insulin, reflecting its role in regulating fat release during energy demand. *Lipoprotein lipase* - This enzyme is primarily located on the **endothelial surface of capillaries** in various tissues, including adipose tissue, muscle, and heart. - Its main role is to clear **triglyceride-rich lipoproteins** like chylomicrons and VLDL from the bloodstream, facilitating the uptake of fatty acids into cells for storage or energy, rather than direct fat metabolism within the adipose cell. *Acid lipase* - **Lysosomal acid lipase** functions within lysosomes to break down cholesterol esters and triglycerides that are taken up by cells. - Its primary role is in the degradation of lipids within the **lysosomal compartments**, not in the primary process of fat mobilization from adipose tissue stores. *Acid maltase* - Also known as **alpha-glucosidase**, this enzyme is a lysosomal enzyme responsible for breaking down glycogen into glucose. - Its function is related to **glycogen metabolism** and has no direct role in fat metabolism in adipose tissue.
Question 177: Which cofactor is primarily associated with the activity of glutamate dehydrogenase?
- A. NAD+ (Correct Answer)
- B. FAD
- C. FMN
- D. FADH2
Explanation: ***NAD+*** - Glutamate dehydrogenase catalyzes the oxidative deamination of **glutamate** to **α-ketoglutarate** and ammonia, and this reaction primarily uses **NAD+** as an electron acceptor. - In some organisms and contexts, it can also use **NADP+**, but **NAD+** is the more common and significant cofactor for its catabolic role. *FAD* - **FAD (flavin adenine dinucleotide)** is typically associated with **flavoproteins** and enzymes involved in oxidation-reduction reactions, such as those in the **electron transport chain** and the **Krebs cycle**. - Enzymes like **succinate dehydrogenase** use FAD, not glutamate dehydrogenase. *FMN* - **FMN (flavin mononucleotide)** is another flavin coenzyme, similar to FAD, and is found in various **flavoproteins** and enzymes of the **electron transport chain**, such as **NADH dehydrogenase (Complex I)**. - It does not serve as a primary cofactor for **glutamate dehydrogenase** activity. *FADH2* - **FADH2** is the reduced form of **FAD**, carrying high-energy electrons to the **electron transport chain** for ATP synthesis. - It's a product or reactant of various metabolic pathways, but not a direct cofactor for **glutamate dehydrogenase**.
Question 178: Which of the following metabolites is involved in glycogenolysis, glycolysis and gluconeogenesis ?
- A. Glucose-6-phosphate (Correct Answer)
- B. Uridine diphosphoglucose
- C. Fructose-6-phosphate
- D. Galactose-1-phosphate
Explanation: ***Glucose-6-phosphate*** - In **glycogenolysis**, **glycogen phosphorylase** breaks down glycogen into **glucose-1-phosphate**, which is then converted into **glucose-6-phosphate** by **phosphoglucomutase**. - In **glycolysis**, **glucose-6-phosphate** is isomerized to **fructose-6-phosphate** by **phosphoglucose isomerase**, committing it to the glycolytic pathway. - In **gluconeogenesis**, **glucose-6-phosphate** is the final product formed from other precursors; it can then be dephosphorylated to free glucose by **glucose-6-phosphatase**. *Galactose-1-phosphate* - This is an intermediate specifically in **galactose metabolism**, not directly involved in the central common pathways of glycogenolysis, glycolysis, or gluconeogenesis. - It is converted to **glucose-1-phosphate** via the **Leloir pathway** (involving **galactose-1-phosphate uridylyltransferase**), which can then enter glycogen metabolism. *Uridine diphosphoglucose* - **UDP-glucose** is crucial for **glycogen synthesis** (**glycogenesis**), serving as the activated glucose donor. - It is not directly a metabolite in the catabolic process of glycogenolysis, nor is it a direct intermediate in glycolysis or gluconeogenesis. *Fructose-6-phosphate* - **Fructose-6-phosphate** is a key intermediate in **glycolysis** and **gluconeogenesis**, specifically downstream from **glucose-6-phosphate**. - However, it is not directly produced from glycogenolysis; **glucose-6-phosphate** is the direct link between glycogenolysis and glycolysis.
Question 179: 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.