NEET-PG 2012 Practice Questions

Q: Nucleus gracilis and nucleus cuneatus are seen in?

Medulla. ***Medulla*** - The **nucleus gracilis** and **nucleus cuneatus** are located in the **dorsal medulla** and are crucial for processing **conscious proprioception**, **vibration**, and **fine touch**. - These nuclei receive input from the fasciculus gracilis and fasciculus cuneatus (dorsal column tracts) and are part of the dorsal column-medial lemniscus pathway. - They give rise to the **internal arcuate fibers** which decussate and form the **medial lemniscus**. *Pons* - The pons contains several important nuclei, including the **pontine nuclei** (involved in motor coordination), nuclei of cranial nerves V, VI, VII, and VIII, and the **locus coeruleus**. - The dorsal column nuclei are not located in the pons. *Temporal lobe* - The **temporal lobe** is part of the cerebral cortex and is primarily involved in **auditory processing**, memory formation, and language comprehension. - It contains structures like the hippocampus and amygdala, but not the dorsal column nuclei. *Midbrain* - The **midbrain** contains nuclei such as the **red nucleus**, **substantia nigra**, and nuclei of cranial nerves III and IV, involved in motor control and eye movements. - The nucleus gracilis and nucleus cuneatus are not found in the midbrain.

Q: Which cranial nerve is not associated with the nucleus ambiguus?

Cranial Nerve XII (Hypoglossal). ***Cranial Nerve XII (Hypoglossal)*** - The **hypoglossal nucleus** in the medulla is the origin for CN XII, which primarily controls **tongue movements** [1]. - It does not receive motor fibers from the nucleus ambiguus, as its function is unrelated to the pharyngeal or laryngeal musculature. *Cranial Nerve X (Vagus)* - Motor fibers for the muscles of the **pharynx** and **larynx** from the nucleus ambiguus contribute to the vagus nerve. - The vagus nerve also provides parasympathetic innervation to the **thoracic and abdominal viscera**. *Cranial Nerve XI (Accessory)* - Cranial root contributions from the nucleus ambiguus exit with the vagus nerve to innervate the **laryngeal muscles**. - The **spinal root** of the accessory nerve, originating from the cervical spinal cord, innervates the **sternocleidomastoid** and **trapezius muscles**. *Cranial Nerve IX (Glossopharyngeal)* - The nucleus ambiguus provides motor innervation for the **stylopharyngeus muscle** via the glossopharyngeal nerve. - This muscle plays a role in **swallowing** and elevates the pharynx.

Q: Which enzyme is primarily associated with the reduction of NADP+ to NADPH in the pentose phosphate pathway?

G6PD. ***G6PD*** - **Glucose-6-phosphate dehydrogenase (G6PD)** catalyzes the first committed step in the pentose phosphate pathway, converting **glucose-6-phosphate** to **6-phosphogluconolactone**. - This reaction involves the reduction of **NADP+ to NADPH**, making G6PD the primary enzyme for NADPH production in this pathway. *APDH* - **APDH (adenosine phosphosulfate reductase)** is involved in sulfur metabolism and has no direct role in the pentose phosphate pathway or NADPH production. - This enzyme primarily functions in prokaryotes for the **reduction of APS (adenosine 5'-phosphosulfate)**. *α-keto glutarate dehydrogenases* - **Alpha-ketoglutarate dehydrogenase** is a mitochondrial enzyme part of the **Krebs cycle**, converting **alpha-ketoglutarate to succinyl-CoA**. - This enzyme is crucial for ATP production and generates **NADH**, not NADPH, in its reaction. *None of the options* - This option is incorrect because **G6PD** is indeed the primary enzyme responsible for NADPH generation in the pentose phosphate pathway.

Q: Which isoenzyme of lactate dehydrogenase (LDH) is predominantly elevated in liver injury?

LDH-5. ***LDH-5 isoenzyme most significant in hepatic conditions*** - **LDH-5** is the predominant isoenzyme found in the **liver** and skeletal muscle. - An elevation of **LDH-5** is highly indicative of **hepatocellular damage** or injury. *LDH-1 isoenzyme associated with cardiac tissue* - **LDH-1** is primarily present in the **heart** and red blood cells. - Its elevation suggests conditions like **myocardial infarction** or hemolytic anemia, not liver injury. *LDH-3 isoenzyme typical in respiratory system* - **LDH-3** is found in the **lungs**, kidneys, and other tissues. - While it can be elevated in **pulmonary embolism** or renal disease, it is not specific for liver injury. *LDH-2 isoenzyme linked to erythrocyte metabolism* - **LDH-2** is abundant in **red blood cells** and also found in the heart and kidneys. - Elevations are often seen in conditions involving **hemolysis** or myocardial damage, similar to LDH-1.

Q: What is the specific activity of an enzyme?

Enzyme units per mg of protein. ***Enzyme units per mg of protein*** - **Specific activity** is defined as the number of **enzyme units** (representing catalytic activity) per milligram of total protein in the sample. - It is a measure of **purity**, indicating the amount of active enzyme relative to other proteins in a preparation. - Formula: Specific activity = Units of enzyme activity / mg of total protein - Used to track enzyme purification progress during isolation procedures. *Concentration of substrate transformed per minute* - This describes the **reaction velocity** or rate of catalysis, but not the specific activity of the enzyme. - While related to enzyme activity, it does not normalize the activity to the amount of **total protein**. - This would be expressed as reaction rate or velocity (V), not specific activity. *Enzyme units per mg of substrate* - This is an incorrect formulation that confuses substrate with protein. - **Specific activity** is normalized to the amount of **protein** in the enzyme preparation, not the substrate. - This option represents a common misconception in enzyme kinetics terminology. *Limit of enzyme per gram of substrate* - This phrase does not correspond to any standard biochemical measure of enzyme activity or concentration. - It does not provide information about the **catalytic efficiency** or **purity** of the enzyme preparation. - The term "limit" is not used in the context of specific activity measurements.

Q: Which of the following pairs of compounds has the highest standard reduction potential?

Fe³⁺/Fe²⁺. ***Fe³⁺/Fe²⁺*** - The **Fe³⁺/Fe²⁺ couple** has a **standard reduction potential (E'0)** of **+0.77 V**, making it the highest among the given options. - A higher positive E'0 indicates a stronger tendency for the oxidized form to accept electrons and be reduced. *NADH/NAD+* - The **NADH/NAD+ couple** has a **standard reduction potential** of **-0.32 V**, indicating it is a strong reducing agent. - Its negative reduction potential means it readily donates electrons during metabolic processes. *Succinate/Fumarate* - The **succinate/fumarate couple** has a **standard reduction potential** of **+0.03 V**. - This pair is involved in the **TCA cycle**, where succinate is oxidized to fumarate, releasing electrons. *Ubiquinone/Ubiquinol* - The **ubiquinone/ubiquinol couple** has a **standard reduction potential** varying around **+0.05 to +0.10 V**, depending on the specific state. - It acts as a mobile electron carrier in the **electron transport chain**, accepting electrons from NADH and FADH2.

Q: Fluoroacetate inhibits?

Aconitase. ***Aconitase*** - **Fluoroacetate** is metabolically converted to **fluorocitrate**, which is a potent competitive inhibitor of **aconitase**. - **Aconitase** is the enzyme responsible for converting **citrate to isocitrate** in the **Krebs cycle**, and its inhibition blocks the cycle. *Citrate synthase* - This enzyme is responsible for the formation of **citrate** from **acetyl-CoA** and **oxaloacetate**. - While fluoroacetate indirectly affects the cycle, it does not directly inhibit **citrate synthase**. *Succinate dehydrogenase* - This enzyme is part of the **Krebs cycle** and the **electron transport chain**, converting **succinate to fumarate**. - **Malonate** is a competitive inhibitor of succinate dehydrogenase, not **fluoroacetate**. *Alpha-ketoglutarate dehydrogenase* - This enzyme catalyzes the conversion of **alpha-ketoglutarate to succinyl-CoA** in the **Krebs cycle**. - Specific inhibitors of this enzyme include **arsenite** and **mercury compounds**, but not fluoroacetate.

Q: Glucose oxidase converts glucose to?

Gluconic acid. ***Gluconic acid*** - **Glucose oxidase** specifically catalyzes the oxidation of glucose, producing **gluconic acid** and hydrogen peroxide. - This reaction forms the basis for many common **glucose diagnostic tests**, such as those used in blood glucose monitors. *Glucuronic acid* - **Glucuronic acid** is formed from the oxidation of glucose at carbon 6, typically through the **uronic acid pathway**. - It is known for its role in **detoxification** and conjugation reactions in the liver, not as a direct product of glucose oxidase. *Galactonic acid* - **Galactonic acid** is an oxidized form of galactose, a different monosaccharide from glucose. - Its formation is not associated with the action of **glucose oxidase**, an enzyme specific to glucose. *Iduronic acid* - **Iduronic acid** is a C5 epimer of glucuronic acid and is a common component of various **glycosaminoglycans** like dermatan sulfate and heparan sulfate. - It is not produced by the action of **glucose oxidase** on glucose.

Q: Increased uric acid levels are seen in which glycogen storage disease ?

Type I (Von Gierke's disease). ***Type I (Von Gierke's disease)*** - In **Von Gierke's disease**, the deficiency of **glucose-6-phosphatase** leads to accumulation of glucose-6-phosphate in hepatocytes. - **Hyperuricemia** occurs due to: 1. **Increased purine degradation** - Metabolic stress leads to accelerated ATP breakdown and increased uric acid production 2. **Decreased renal excretion** - Lactic acidosis (from G6P → pyruvate → lactate) competitively inhibits uric acid secretion in renal tubules 3. **Enhanced purine synthesis** - Increased availability of ribose-5-phosphate from pentose phosphate pathway - Classic triad: **Hepatomegaly, hypoglycemia, and lactic acidosis with hyperuricemia** *Type II (Pompe disease)* - Caused by a deficiency of **acid alpha-glucosidase** (acid maltase), leading to glycogen accumulation in **lysosomes**. - Primarily affects the **heart**, **muscles**, and **liver**, but does not cause hyperuricemia. *Type IV (Andersen disease)* - Results from a deficiency of **glycogen branching enzyme**, leading to the formation of abnormal glycogen with long, unbranched chains. - Primarily affects the **liver** and **spleen**, causing cirrhosis and hepatic failure, but not hyperuricemia. *Type III (Cori disease)* - Caused by a deficiency of **glycogen debranching enzyme** (amylo-1,6-glucosidase), leading to abnormal accumulation of glycogen with short outer branches. - Presents with hepatomegaly, hypoglycemia, and muscle weakness, but **hyperuricemia is not a characteristic feature**.

Q: Which of the following is required for fatty acid synthesis ?

NADPH. ***NADPH*** - **NADPH** is crucial for fatty acid synthesis, providing the **reducing power** needed for the successive reduction steps. - The enzymes involved, such as **fatty acid synthase**, utilize **NADPH** for the conversion of keto groups to hydroxyl groups and then to saturated methylene groups. *NADH* - **NADH** plays a primary role in **oxidative phosphorylation** and the electron transport chain to generate ATP. - It is generally produced during **catabolic reactions** and is not primarily used as a reducing agent in anabolic processes like fatty acid synthesis. *FADH* - **FADH2** (reduced form of FAD, not FADH) is a coenzyme involved in redox reactions, particularly in the **Krebs cycle** and beta-oxidation of fatty acids. - Like NADH, it is mostly involved in **catabolic processes** that generate energy, rather than anabolic processes requiring reducing equivalents for synthesis. *None of the options* - This option is incorrect because **NADPH** is indeed required for fatty acid synthesis, serving as the essential reducing agent. - The other coenzymes mentioned (NADH, FADH) have different metabolic roles, primarily in energy production rather than biosynthesis.

Question 1

Nucleus gracilis and nucleus cuneatus are seen in?

Accepted Answer

Medulla

Answer

Temporal lobe

Answer

Midbrain

Answer

Pons

Question 2

Which cranial nerve is not associated with the nucleus ambiguus?

Accepted Answer

Cranial Nerve XII (Hypoglossal)

Answer

Cranial Nerve X (Vagus)

Answer

Cranial Nerve XI (Accessory)

Answer

Cranial Nerve IX (Glossopharyngeal)

Question 3

Which enzyme is primarily associated with the reduction of NADP+ to NADPH in the pentose phosphate pathway?

Accepted Answer

G6PD

Answer

APDH

Answer

α-keto glutarate dehydrogenases

Answer

None of the options

Question 4

Which isoenzyme of lactate dehydrogenase (LDH) is predominantly elevated in liver injury?

Accepted Answer

LDH-5

Answer

LDH-3

Answer

LDH-1

Answer

LDH-2

Question 5

What is the specific activity of an enzyme?

Accepted Answer

Enzyme units per mg of protein

Answer

Concentration of substrate transformed per minute

Answer

Enzyme units per mg of substrate

Answer

Limit of enzyme per gram of substrate

Question 6

Which of the following pairs of compounds has the highest standard reduction potential?

Accepted Answer

Fe³⁺/Fe²⁺

Answer

NADH/NAD+

Answer

Succinate/Fumarate

Answer

Ubiquinone/Ubiquinol

Question 7

Fluoroacetate inhibits?

Accepted Answer

Aconitase

Answer

Citrate synthase

Answer

Succinate dehydrogenase

Answer

Alpha-ketoglutarate dehydrogenase

Question 8

Glucose oxidase converts glucose to?

Accepted Answer

Gluconic acid

Answer

Glucuronic acid

Answer

Galactonic acid

Answer

Iduronic acid

Question 9

Increased uric acid levels are seen in which glycogen storage disease ?

Accepted Answer

Type I (Von Gierke's disease)

Answer

Type II (Pompe disease)

Answer

Type IV (Andersen disease)

Answer

Type III (Cori disease)

Question 10

Which of the following is required for fatty acid synthesis ?

Accepted Answer

NADPH

Answer

NADH

Answer

FADH₂

Answer

None of the options

NEET-PG 2012

Anatomy

Biochemistry