Anatomy
1 questionsWhere do primitive red blood cells first originate during early embryonic development?
NEET-PG 2015 - Anatomy NEET-PG Practice Questions and MCQs
Question 261: Where do primitive red blood cells first originate during early embryonic development?
- A. Liver
- B. Yolk sac (Correct Answer)
- C. Bone marrow
- D. Spleen
Explanation: ***Yolk sac*** - The **yolk sac** is the primary site of **hematopoiesis** during the first few weeks of embryonic development. - Primitive erythroid cells (red blood cells) originate here to supply the developing embryo with oxygen. *Liver* - The **liver** takes over as the main hematopoietic organ from about the 6th week of gestation, after the yolk sac [1]. - While it produces various blood cells, it is not the *first* site of primitive red blood cell formation. *Bone marrow* - **Bone marrow** becomes the primary site of hematopoiesis during the **fetal period** (around the 20th to 24th week) and continues throughout postnatal life [2]. - It is not involved in the initial production of primitive red blood cell formation in early embryogenesis. *Spleen* - The **spleen** plays a minor role in fetal hematopoiesis, mainly producing lymphoid cells and some myeloid cells, and can take on myeloid functions if the bone marrow is compromised. - It is not the initial site of red blood cell production in the early embryo.
Biochemistry
4 questionsWhich of the following statements are true regarding the visual cycle cascade?
In the malate shuttle, how many ATPs are produced from one NADH?
Which method is used to separate a mixture of lipids?
Which of the following stimulates Acetyl CoA Carboxylase?
NEET-PG 2015 - Biochemistry NEET-PG Practice Questions and MCQs
Question 261: Which of the following statements are true regarding the visual cycle cascade?
- A. All of the options are true (Correct Answer)
- B. Light causes isomerization of 11-cis-retinal to all-trans-retinal
- C. Retinal is involved in the visual cycle
- D. Involves a conformational change in opsin
Explanation: ***All of the statements are true*** The visual cycle cascade involves multiple interconnected events in phototransduction: **Light causes isomerization of 11-cis-retinal to all-trans-retinal** - This is the **primary photochemical event** that initiates vision - Light absorption causes the **cis-trans isomerization** in less than a picosecond - This conformational change is the only light-dependent step in the entire cascade **Retinal is involved in the visual cycle** - **11-cis-retinal** serves as the chromophore bound to opsin forming rhodopsin - After isomerization to **all-trans-retinal**, it must be converted back to 11-cis-retinal - This regeneration occurs through the **retinoid cycle** involving RPE cells **Involves a conformational change in opsin** - The isomerization of retinal triggers **conformational changes in opsin** - This converts rhodopsin to **metarhodopsin II** (the active form) - Activated opsin then activates **transducin** (G-protein), amplifying the signal and leading to hyperpolarization of photoreceptor cells All three statements accurately describe essential components of the visual cycle cascade.
Question 262: In the malate shuttle, how many ATPs are produced from one NADH?
- A. 1 ATP
- B. 3 ATP
- C. 2 ATP
- D. 2.5 ATP (Correct Answer)
Explanation: ***2.5 ATP*** - In the **malate-aspartate shuttle**, mitochondrial **NADH** is regenerated from cytosolic NADH, and then enters the electron transport chain at **Complex I**. - **Complex I** entry means that NADH contributes to the pumping of enough protons to generate approximately **2.5 ATP** through oxidative phosphorylation. *1 ATP* - **1 ATP** is not the direct equivalent produced from the reoxidation of one NADH via the malate shuttle into the electron transport chain. - This value is typically associated with the direct hydrolysis of **ATP** or the energy equivalent of **GTP** produced in the citric acid cycle. *3 ATP* - Historically, **3 ATP** was the accepted stoichiometry for one NADH, but more accurate measurements of proton pumping and ATP synthase activity have revised this. - The value of 3 ATP per NADH does not reflect the most current understanding of mitochondrial bioenergetics. *2 ATP* - **2 ATP** is the approximate yield for **FADH2** entering the electron transport chain at **Complex II**, bypassing Complex I, and thus pumping fewer protons. - This value is not applicable to NADH transferred via the malate-aspartate shuttle, as NADH enters at Complex I.
Question 263: Which method is used to separate a mixture of lipids?
- A. Electrophoresis
- B. Chromatography (Correct Answer)
- C. Isoelectric focusing
- D. PAGE
Explanation: ***Chromatography*** - **Chromatography** (e.g., thin-layer chromatography, gas chromatography, high-performance liquid chromatography) is widely used to separate lipids based on differences in their **polarity**, **molecular weight**, or **solubility** in various solvents. - This method allows for the isolation and identification of different lipid classes and individual lipid species from a complex mixture. *Electrophoresis* - **Electrophoresis** separates molecules based on their **charge** and **size** in an electric field, making it more commonly used for proteins and nucleic acids. - Lipids are generally **uncharged** or have very low charge, which makes them poorly suited for separation by standard electrophoretic methods without modification. *Isoelectric focusing* - **Isoelectric focusing** is a type of electrophoresis that separates molecules based on their **isoelectric point (pI)**, which is the pH at which a molecule has no net charge. - This technique is primarily used for **proteins** and **peptides**, as lipids typically lack ionizable groups necessary for establishing a distinct pI. *PAGE* - **PAGE** (Polyacrylamide Gel Electrophoresis) is a common method used to separate **proteins** and **nucleic acids** based on their size and charge. - Lipids are **hydrophobic** and do not readily migrate through an aqueous polyacrylamide gel matrix, making PAGE unsuitable for their direct separation.
Question 264: Which of the following stimulates Acetyl CoA Carboxylase?
- A. Starvation
- B. Glucagon
- C. Citrate (Correct Answer)
- D. None of the options
Explanation: ***Citrate*** - **Citrate** is an allosteric activator of **Acetyl-CoA Carboxylase (ACC)**, indicating abundant energy and precursor availability for fatty acid synthesis. - This activation promotes the conversion of **Acetyl-CoA** to **Malonyl-CoA**, the committed step in **fatty acid synthesis**. *Starvation* - **Starvation** leads to energy deficit, which generally **inhibits** anabolic processes like fatty acid synthesis. - In this state, enzymes involved in anabolic pathways are often downregulated or inhibited to conserve energy. *Glucagon* - **Glucagon** is a hormone that signals low blood glucose and promotes catabolic processes such as **glycogenolysis** and **gluconeogenesis**. - It **inhibits** fatty acid synthesis by phosphorylating and inactivating **Acetyl-CoA Carboxylase**, thus opposing citrate's activating effect. *None of the options* - **Citrate** is a known stimulator of Acetyl CoA Carboxylase. - This option is incorrect because there is a correct answer among the choices.
Physiology
5 questionsWhat does the transient response observed during the insertion of an electrode in electromyography (EMG) indicate?
What do motor evoked potentials primarily assess?
Which of the following is not a component of a mature sperm cell?
Which protein primarily contributes to oncotic pressure in the blood?
Increase in plasma viscosity is maximally caused by which plasma protein?
NEET-PG 2015 - Physiology NEET-PG Practice Questions and MCQs
Question 261: What does the transient response observed during the insertion of an electrode in electromyography (EMG) indicate?
- A. Spontaneous muscle activity
- B. Voluntary muscle contraction
- C. Cell membrane disruption (Correct Answer)
- D. Induced muscle contraction
Explanation: **Cell membrane disruption** - The **transient response** observed during electrode insertion in **EMG** is caused by the mechanical trauma of the needle disrupting the **muscle fiber cell membranes**. - This disruption leads to a brief depolarization and subsequent repolarization of the affected fibers, generating characteristic electrical activity. *Spontaneous muscle activity* - **Spontaneous muscle activity**, such as **fibrillation potentials** or **positive sharp waves**, occurs independently of electrode insertion. - While observed during EMG, these are indicative of **denervation** or **myopathy** and are not directly caused by the act of insertion itself. *Voluntary muscle contraction* - **Voluntary muscle contraction** is recorded when the patient actively contracts the muscle and results in **motor unit action potentials (MUAPs)**. - This is a distinct process from the transient activity produced by electrode insertion. *Induced muscle contraction* - **Induced muscle contraction** typically refers to activity caused by **nerve stimulation** (e.g., in nerve conduction studies) or direct electrical stimulation of the muscle. - This is not the mechanism for the transient response during simple electrode insertion.
Question 262: What do motor evoked potentials primarily assess?
- A. Central motor pathways (Correct Answer)
- B. Both central and peripheral motor pathways
- C. Muscle regeneration
- D. Peripheral motor pathways
Explanation: ***Central motor pathways*** - **Motor evoked potentials (MEPs)** are generated by electrical or magnetic stimulation of the **motor cortex** and primarily assess the integrity of **central motor pathways**, specifically the **corticospinal tracts**. - MEPs are the **gold standard** for monitoring **upper motor neuron** function during neurosurgical and spinal procedures. - The technique is most sensitive to dysfunction in the **brain and spinal cord** (central nervous system), making this their primary clinical utility. *Peripheral motor pathways* - While MEPs do eventually activate peripheral motor neurons to produce muscle responses, they are **not the primary tool** for assessing peripheral pathways. - **Nerve conduction studies (NCS)** and **electromyography (EMG)** are direct and more specific measures for evaluating peripheral motor nerve function. *Both central and peripheral motor pathways* - Although MEPs provide information about the entire motor pathway from cortex to muscle, their **primary diagnostic strength and clinical application** is in detecting dysfunction within the **central nervous system**. - The latency and amplitude of MEPs are most sensitive to **conduction abnormalities along the corticospinal tract**, not peripheral nerves. *Muscle regeneration* - MEPs do **not assess muscle regeneration** or intrinsic muscle health. - **Electromyography (EMG)** with needle examination and **muscle biopsy** are the appropriate methods to evaluate muscle regeneration and myopathic processes.
Question 263: Which of the following is not a component of a mature sperm cell?
- A. Lysosome
- B. Golgi apparatus
- C. Mitochondria
- D. Endoplasmic reticulum (Correct Answer)
Explanation: ***Endoplasmic reticulum*** - The **endoplasmic reticulum** is prominent in spermatogonia and spermatocytes but largely absent in **mature sperm** as organelles are shed during spermiogenesis to reduce cell volume. - Its primary functions of protein synthesis and lipid metabolism are not required in a terminally differentiated, motile cell like a mature sperm. *Golgi apparatus* - The **Golgi apparatus** reorganizes during spermiogenesis to form the **acrosome**, which is a crucial structure for fertilization. - While the distinct Golgi stacks are not present, its modified derivative, the acrosome, is an essential component. *Mitochondria* - **Mitochondria** are abundant in the midpiece of the sperm tail, arranged in a spiral sheath. - They are vital for generating the **ATP** required for the flagellum's motility, enabling the sperm to swim. *Lysosome* - Although typical lysosomes are not found, the **acrosome** of the sperm is considered a modified lysosome. - The acrosome contains **hydrolytic enzymes** similar to lysosomes, which are critical for penetrating the egg's outer layers during fertilization.
Question 264: Which protein primarily contributes to oncotic pressure in the blood?
- A. Albumin (Correct Answer)
- B. Globulins
- C. Fibrinogen
- D. Transferrin
Explanation: ***Albumin*** - **Albumin** is the most abundant plasma protein and its small size and high concentration make it the primary determinant of **oncotic pressure** in the blood. - Its presence in the capillaries draws water from the **interstitial space** back into the blood vessels, maintaining **fluid balance** and blood volume. *Fibrinogen* - **Fibrinogen** is a crucial protein involved in **blood clotting**, where it is converted into **fibrin** to form a clot. - While a plasma protein, its contribution to **oncotic pressure** is minor compared to albumin, as it's less abundant and larger in size. *Globulins* - **Globulins** are a diverse group of proteins involved in immune function (**immunoglobulins**), transport (e.g., **alpha** and **beta globulins**), and clotting. - While they contribute to total plasma protein concentration, their collective impact on **oncotic pressure** is secondary to that of albumin due to lower concentrations and varied molecular weights. *Transferrin* - **Transferrin** is a specific **beta-globulin** that plays a vital role in **iron transport** in the blood. - Its primary function is not related to **oncotic pressure**, and its concentration is significantly lower than albumin.
Question 265: Increase in plasma viscosity is maximally caused by which plasma protein?
- A. Albumin
- B. All have equal effect
- C. Globulin
- D. Fibrinogen (Correct Answer)
Explanation: ***Globulin*** - Increased levels of **globulin** proteins, particularly in inflammatory or proliferative conditions, have a significant impact on plasma viscosity due to their **high molecular weight** [1]. - **Globulins** contribute to **hyperviscosity syndrome**, which can lead to clinical symptoms like fatigue and visual disturbances [1]. *Albumin* - While **albumin** is the most abundant plasma protein, its primary role is in maintaining **oncotic pressure**, not significantly affecting plasma viscosity. - An increase in albumin does not correlate with plasma viscosity increases to the extent seen with globulins. *All have equal effect* - Different plasma proteins do not have **equal effects** on viscosity; **globulins** and **fibrinogen** particularly influence it more than **albumin**. - The impact on viscosity varies significantly with protein concentration and type, making this statement inaccurate. *Fibrinogen* - **Fibrinogen** does contribute to plasma viscosity but is typically less than that caused by globulins, especially when globulin levels are markedly elevated. - Its effect is more pronounced during **coagulation**, rather than in the general increase of plasma viscosity associated with inflammatory states. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 141-142.