General Physiology Practice Questions

Q: Which of the following is NOT a marker of mitochondria?

5-nucleotidase. **Explanation:** The correct answer is **B. 5-nucleotidase**. In cell biology, "marker enzymes" are specific enzymes localized exclusively or predominantly within a particular organelle. They are used to identify and assess the purity of organelles during cell fractionation. 1. **Why 5-nucleotidase is the correct answer:** **5-nucleotidase** is a classic marker enzyme for the **plasma membrane**. It is also found in the lysosomes but is never associated with the mitochondria. Its primary role is the conversion of nucleoside 5′-monophosphates to nucleosides. 2. **Analysis of Incorrect Options (Mitochondrial Markers):** * **ATP synthase (Complex V):** Located on the inner mitochondrial membrane; it is the functional marker for oxidative phosphorylation. * **Glutamate dehydrogenase:** A key enzyme for amino acid metabolism located specifically in the **mitochondrial matrix**. * **Creatine kinase (CK):** Specifically, the **mitochondrial isoenzyme of CK (m-CK)** is found in the intermembrane space. It plays a vital role in the "creatine phosphate shuttle" for energy transport. **High-Yield Markers for NEET-PG:** To excel in General Physiology and Biochemistry, remember these specific organelle markers: * **Mitochondria:** Succinate dehydrogenase (Inner membrane—most specific), Cytochrome oxidase, Malate dehydrogenase (Matrix). * **Plasma Membrane:** Na⁺-K⁺ ATPase, Adenylate cyclase, 5-nucleotidase. * **Lysosomes:** Acid phosphatase. * **Golgi Apparatus:** Galactosyltransferase. * **Endoplasmic Reticulum:** Glucose-6-phosphatase (Smooth ER), Cytochrome P450. * **Peroxisomes:** Catalase, Urate oxidase. * **Cytosol:** Lactate dehydrogenase (LDH).

Q: Which protein is responsible for copper binding?

Ceruloplasmin. **Explanation:** **Ceruloplasmin** is the correct answer because it is the primary copper-carrying protein in the blood, accounting for approximately **90-95% of total plasma copper**. Synthesized in the liver, it is an alpha-2 globulin that functions as a ferroxidase enzyme, oxidizing ferrous iron ($Fe^{2+}$) to ferric iron ($Fe^{3+}$) to facilitate its binding to transferrin. **Analysis of Incorrect Options:** * **Albumin (A):** While albumin binds many substances (bilirubin, calcium, drugs), it only carries about 5-10% of plasma copper. This "loosely bound" copper is the fraction that is more easily taken up by tissues. * **Globulin (B):** This is a broad category of proteins. While ceruloplasmin is a type of alpha-2 globulin, "globulin" as a general term is non-specific. * **Transferrin (C):** This protein is specifically responsible for the transport of **Iron**, not copper. **Clinical Pearls for NEET-PG:** * **Wilson’s Disease:** Characterized by a deficiency in **ATP7B** (a copper-transporting ATPase), leading to decreased incorporation of copper into apoceruloplasmin. This results in **low serum ceruloplasmin levels** and toxic copper accumulation in the liver and basal ganglia (Kayser-Fleischer rings). * **Menkes Disease:** An X-linked recessive disorder caused by a mutation in **ATP7A**, leading to impaired intestinal copper absorption and "kinky hair" syndrome. * **Acute Phase Reactant:** Ceruloplasmin levels rise during inflammation, infection, or pregnancy.

Q: What is the primary function of a muscle spindle?

Receptor for the stretch reflex. **Explanation:** The **muscle spindle** is a specialized sensory receptor located within the belly of skeletal muscles, arranged in parallel with extrafusal fibers. Its primary function is to detect changes in **muscle length** and the rate of change in length. **1. Why Option A is Correct:** When a muscle is stretched, the muscle spindle is also stretched, triggering action potentials in **Type Ia (primary) and Type II (secondary) afferent fibers**. These fibers synapse directly (monosynaptically) with alpha motor neurons in the spinal cord, causing the stretched muscle to contract. This mechanism is the basis of the **stretch reflex** (e.g., the knee-jerk reflex). **2. Why Other Options are Incorrect:** * **Option B:** While muscle spindles contribute to maintaining posture, the "antigravity" function is a broader physiological outcome involving various reflexes and the cerebellum, not the primary definition of the spindle's function. * **Option C:** The stretch reflex is the classic example of a **monosynaptic reflex** (the fastest in the body). Multisynaptic pathways are characteristic of the Golgi Tendon Organ (inverse stretch reflex) or the withdrawal reflex. * **Option D:** Muscle spindles are excited by **stretch**, but they are actually **silenced/unloaded during active contraction** of the extrafusal fibers (unless alpha-gamma co-activation occurs to maintain sensitivity). **High-Yield NEET-PG Pearls:** * **Location:** In parallel with extrafusal fibers (detects length). * **Innervation:** Sensory via **Ia and II** fibers; Motor via **Gamma motor neurons** (which maintain spindle sensitivity). * **Contrast:** The **Golgi Tendon Organ (GTO)** is in series with muscle fibers, detects **tension**, and uses **Ib afferents** for the disynaptic inverse stretch reflex. * **Nuclear Bag fibers** detect dynamic changes (velocity), while **Nuclear Chain fibers** detect static changes (length).

Q: Knee joint pain in a deep-sea diver is most likely due to which of the following?

Increased nitrogen partial pressure. ### Explanation The clinical presentation of knee joint pain in a deep-sea diver is a classic manifestation of **Decompression Sickness (DCS)**, also known as "The Bends" or Caisson disease. **Why Nitrogen Partial Pressure is Correct:** According to **Henry’s Law**, the amount of gas dissolved in a liquid is proportional to its partial pressure. At high pressures (deep sea), large amounts of **Nitrogen** (which is physiologically inert) dissolve into the blood and fatty tissues. If the diver ascends too rapidly, the ambient pressure drops quickly, and the dissolved nitrogen comes out of solution to form **bubbles** in the blood and tissues. When these bubbles form in the synovial fluid and periarticular tissues of large joints (like the knee or shoulder), they cause severe localized pain. **Analysis of Incorrect Options:** * **A & B (Oxygen and CO₂):** While high partial pressures of Oxygen can cause CNS toxicity (Paul Bert effect), and CO₂ can cause narcosis, neither is responsible for bubble formation during ascent. These gases are metabolically active and are rapidly utilized or buffered by the body. * **C (Nitrous Oxide):** This is an anesthetic gas not typically present in standard diving breathing mixtures (which are usually compressed air, Heliox, or Nitrox). **High-Yield Clinical Pearls for NEET-PG:** * **Type I DCS:** Involves "The Bends" (joint pain) and "Skin Bends" (pruritus/rashes). * **Type II DCS:** More severe; involves the CNS (paralysis) and the lungs ("The Chokes" – dyspnea and cough). * **Nitrogen Narcosis:** Occurs at depth (high pressure) and is often called "Rapture of the Deep," resembling alcohol intoxication. * **Treatment:** The definitive treatment for DCS is **Hyperbaric Oxygen Therapy (HBOT)** to reduce bubble size and enhance nitrogen washout.

Q: What is the correct sequence of vesicle transport starting from the Endoplasmic Reticulum (ER)?

ER - Cis Golgi - Trans Golgi - Cell membrane. ### Explanation **1. Why Option B is Correct:** The secretory pathway follows a unidirectional flow known as **anterograde transport**. Proteins are synthesized in the **Rough Endoplasmic Reticulum (RER)** and packaged into COPII-coated vesicles. These vesicles first enter the **Cis-Golgi network** (the receiving side facing the ER). As proteins undergo post-translational modifications (like glycosylation), they move through the medial cisternae to the **Trans-Golgi network** (the shipping side). From here, they are sorted into secretory vesicles that fuse with the **cell membrane** for exocytosis or incorporation. **2. Why Other Options are Incorrect:** * **Option A & C:** These suggest that vesicles move from Trans to Cis or bypass the Golgi polarity. In physiological conditions, the Cis-face always receives material from the ER, while the Trans-face exports it. * **Option D:** This reverses the initial step. The ER is the site of protein synthesis; the Golgi acts only as a processing and "post-office" center. Transport cannot begin at the Golgi. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Vesicle Coats:** * **COPII:** Anterograde transport (ER → Golgi). *Mnemonic: "Two (II) steps forward."* * **COPI:** Retrograde transport (Golgi → ER). *Mnemonic: "One (I) step back."* * **Clathrin:** Transport from Trans-Golgi to lysosomes and endocytosis from the plasma membrane. * **I-Cell Disease:** A clinical correlation where a deficiency in phosphorylating mannose residues (in the Golgi) leads to failure of protein trafficking to lysosomes, causing enzymes to be secreted extracellularly instead. * **Golgi Marker:** **Nucleoside diphosphatase** is the characteristic biochemical marker for the Golgi apparatus.

Q: Each hemoglobin molecule contains how many polypeptide chains and how many heme groups?

4 polypeptide chains with 4 heme groups. **Explanation** **Underlying Concept:** Hemoglobin (Hb) is a globular protein with a **quaternary structure**. Adult hemoglobin (HbA) is a tetramer consisting of **four polypeptide chains** (two alpha and two beta chains). Each of these polypeptide chains is covalently linked to a **single heme group**. Therefore, one complete hemoglobin molecule contains four polypeptide chains and four heme groups. **Why the Correct Answer is Right:** * **4 Polypeptide Chains:** The globin portion consists of four subunits. In adults, this is typically $\alpha_2\beta_2$. * **4 Heme Groups:** Each globin chain contains a hydrophobic pocket that holds one heme moiety. Since there are four chains, there are four heme groups. * **Oxygen Binding:** Each heme group contains one iron atom ($Fe^{2+}$) in the ferrous state, which can bind one molecule of $O_2$. Thus, one hemoglobin molecule can carry a maximum of **four molecules of $O_2$** (8 atoms of oxygen). **Why Incorrect Options are Wrong:** * **Options A & C:** These suggest only 2 polypeptide chains. This describes a dimer, not the functional tetrameric structure of hemoglobin. * **Options B:** While it correctly identifies 4 chains, it underestimates the heme groups. Each chain must have its own heme group to function in oxygen transport. **NEET-PG High-Yield Pearls:** 1. **Iron State:** Iron must be in the **Ferrous ($Fe^{2+}$)** state to bind oxygen. If oxidized to the **Ferric ($Fe^{3+}$)** state, it forms **Methemoglobin**, which cannot bind $O_2$. 2. **Cooperativity:** The binding of the first $O_2$ molecule increases the affinity for subsequent $O_2$ molecules (Sigmoid-shaped dissociation curve). 3. **Hb Variants:** HbF (Fetal) consists of $\alpha_2\gamma_2$ and has a higher affinity for $O_2$ than HbA. 4. **2,3-BPG:** This molecule binds to the central cavity of the deoxy-Hb tetramer, stabilizing the "T" (Tense) state and promoting $O_2$ unloading.

Q: Which of the following proteins acts as a cGMP?

Atrial natriuretic peptide. ### Explanation **Correct Option: A (Atrial Natriuretic Peptide)** The question refers to the signaling pathway utilized by specific hormones. **Atrial Natriuretic Peptide (ANP)** and Brain Natriuretic Peptide (BNP) exert their physiological effects by binding to membrane-bound receptors (NPR-A) that possess intrinsic **guanylyl cyclase** activity. This activation converts GTP into **cyclic GMP (cGMP)**, which acts as the second messenger. cGMP then activates Protein Kinase G (PKG), leading to vasodilation and natriuresis. Other substances using the cGMP pathway include Nitric Oxide (via soluble guanylyl cyclase). **Incorrect Options:** * **B. G-protein:** These are molecular switches (e.g., Gs, Gi, Gq) that link receptors to various effectors like adenylyl cyclase or phospholipase C. While some G-proteins lead to cAMP production, they are transducers, not the second messenger itself. * **C. Glycoprotein:** This is a structural classification of proteins containing oligosaccharide chains (e.g., TSH, LH, FSH). It describes the chemical nature of the hormone, not its signaling mechanism. * **D. Mucoprotein:** These are proteins conjugated with glycosaminoglycans (like those found in mucus). They do not function as signaling molecules in the context of second messenger systems. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for cGMP:** "**ANP** & **NO** go to the **G**ym" (ANP and Nitric Oxide use cGMP). * **Phosphodiesterase-5 (PDE-5) inhibitors** (e.g., Sildenafil) work by preventing the breakdown of cGMP, prolonging vasodilation. * Most peptide hormones use **cAMP** (e.g., ACTH, Glucagon, PTH) or **IP3/DAG** (e.g., Oxytocin, GnRH), making the cGMP-mediated hormones a high-yield exception.

Question 1

Which of the following is NOT a marker of mitochondria?

Accepted Answer

5-nucleotidase

Answer

ATP synthase

Answer

Glutamate dehydrogenase

Answer

Creatine kinase

Question 2

Free water clearance by the kidney is increased by which of the following?

Accepted Answer

Diabetes insipidus

Answer

Renal failure

Answer

Diuretic therapy

Answer

Diabetes mellitus

Question 3

What causes muscle contraction?

Accepted Answer

Release of acetylcholine

Answer

Release of noradrenaline

Answer

Release of serotonin

Answer

Release of histamine

Question 4

Which protein is responsible for copper binding?

Accepted Answer

Ceruloplasmin

Answer

Albumin

Answer

Globulin

Answer

Transferrin

Question 5

What property of the postsynaptic neuron would optimize the effectiveness of two closely spaced axodendritic synapses?

Accepted Answer

A high membrane resistance

Answer

A high dendritic cytoplasmic resistance

Answer

A small cross-sectional area

Answer

A small space constant

Question 6

What is the primary function of a muscle spindle?

Accepted Answer

Receptor for the stretch reflex

Answer

Involved in antigravity muscle function

Answer

Part of a multisynaptic reflex pathway

Answer

Excited by both stretch and contraction of the muscle

Question 7

Knee joint pain in a deep-sea diver is most likely due to which of the following?

Accepted Answer

Increased nitrogen partial pressure

Answer

Increased oxygen partial pressure

Answer

Increased carbon dioxide partial pressure

Answer

Increased nitrous oxide partial pressure

Question 8

What is the correct sequence of vesicle transport starting from the Endoplasmic Reticulum (ER)?

Accepted Answer

ER - Cis Golgi - Trans Golgi - Cell membrane

Answer

ER - Trans Golgi - Cis Golgi - Lysosomes

Answer

ER - Lysosomes - Trans Golgi - Cis Golgi

Answer

Cis Golgi - ER - Trans Golgi - Cell membrane

Question 9

Each hemoglobin molecule contains how many polypeptide chains and how many heme groups?

Accepted Answer

4 polypeptide chains with 4 heme groups

Answer

2 polypeptide chains with 2 heme groups

Answer

4 polypeptide chains with 2 heme groups

Answer

2 polypeptide chains with 4 heme groups

Question 10

Which of the following proteins acts as a cGMP?

Accepted Answer

Atrial natriuretic peptide

Answer

G-protein

Answer

Glycoprotein

Answer

Mucoprotein

General Physiology — MCQs

General Physiology — MCQs

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