Cell-to-Cell Communication — MCQs
What is the role of gap junctions in cardiac muscle function?
Some cells secrete chemicals into the extracellular fluid that act on cells in the same tissue. Which of the following refers to this type of regulation?
Which of the following act through tyrosine kinase receptor:
Which of the following neurotransmitters is primarily released from the sympathetic nervous system to increase heart rate in response to a DECREASE in blood pressure?
Which of the following statements best describes the mechanism of action of insulin on target cells?
Which of the following binds to intracellular receptors?
Cell-to-cell permeability occurs through
Which of the following statements accurately describes G proteins?
Prokaryotes do not have
Which of the following is a major component of the plasma membrane?
Cell-to-Cell Communication Indian Medical PG Practice Questions and MCQs
Question 1: What is the role of gap junctions in cardiac muscle function?
- A. Are not found in cardiac muscles
- B. Are not found in smooth muscles
- C. Have no significant role in cardiac muscle function
- D. Facilitate impulse transmission between cardiac myocytes (Correct Answer)
Explanation: ***Facilitate impulse transmission between cardiac myocytes*** - **Gap junctions** are specialized channels between adjacent cells that allow for direct communication and rapid movement of **ions** and small molecules. - In cardiac muscle, they form an essential part of **intercalated discs**, enabling the heart to function as a **syncytium** by allowing electrical impulses to spread quickly from one myocyte to another. *Are not found in cardiac muscles* - This statement is incorrect; **gap junctions** are a defining feature of **cardiac muscle** and are crucial for its coordinated contraction. - They are located within the **intercalated discs** that connect individual cardiac muscle cells. *Are not found in smooth muscles* - This statement is incorrect; **gap junctions** are indeed found in **smooth muscle**, particularly in single-unit smooth muscle, where they contribute to synchronized contractions, such as in the **gastrointestinal tract**. - They allow for the rapid propagation of electrical signals, leading to coordinated muscle activity. *Have no significant role in cardiac muscle function* - This statement is incorrect; **gap junctions** play a critically significant role in cardiac muscle function by ensuring the **rapid and synchronized spread of electrical impulses**. - Without functional gap junctions, the heart would not be able to contract efficiently or effectively as a pump.
Question 2: Some cells secrete chemicals into the extracellular fluid that act on cells in the same tissue. Which of the following refers to this type of regulation?
- A. Neural
- B. Endocrine
- C. Neuroendocrine
- D. Paracrine (Correct Answer)
Explanation: ***Paracrine*** - **Paracrine signaling** involves chemical messengers, or **paracrine factors**, that act on **neighboring cells** within the **same tissue** without entering the bloodstream. - This type of regulation is crucial for local communication and coordination, such as in wound healing or immune responses. *Neural* - **Neural regulation** involves communication via **neurons** that transmit **electrical signals** (action potentials) and release **neurotransmitters** at synapses. - Neurotransmitters act on target cells, which can be distant from the neuron, for rapid and precise responses throughout the body. *Endocrine* - **Endocrine regulation** involves glands that secrete **hormones** directly into the **bloodstream**, which then travel to distant target cells in other tissues or organs. - This form of signaling leads to widespread and long-lasting effects, such as growth regulation or metabolic control. *Neuroendocrine* - **Neuroendocrine regulation** is a hybrid system where specialized **neurons** (neurosecretory cells) release **hormones** into the **bloodstream**, rather than releasing neurotransmitters into a synapse. - An example is the hypothalamus secreting ADH and oxytocin, which act on distant target organs.
Question 3: Which of the following act through tyrosine kinase receptor:
- A. GH
- B. FSH
- C. Glucagon
- D. Insulin (Correct Answer)
Explanation: ***Insulin*** - **Insulin** binds to its specific receptor, which is a **tyrosine kinase receptor**, leading to autophosphorylation and activation of downstream signaling pathways. - This activation results in glucose uptake, metabolism, and storage in target cells. *GH* - **Growth Hormone (GH)** primarily acts through **JAK/STAT signaling pathways** after binding to its receptor, which is a cytokine receptor, not a direct tyrosine kinase receptor. - The GH receptor itself does not possess intrinsic tyrosine kinase activity but rather recruits and activates associated kinases. *FSH* - **Follicle-stimulating hormone (FSH)** mediates its effects by binding to a **G protein-coupled receptor (GPCR)** on target cells. - Activation of the **GPCR** leads to the generation of **cAMP** as a second messenger, which then modulates cellular processes. *Glucagon* - **Glucagon** also acts through a **G protein-coupled receptor (GPCR)** on liver cells. - Binding of glucagon to its receptor activates **adenylyl cyclase**, leading to an increase in **cAMP** levels and subsequently increased glycogenolysis and gluconeogenesis.
Question 4: Which of the following neurotransmitters is primarily released from the sympathetic nervous system to increase heart rate in response to a DECREASE in blood pressure?
- A. Norepinephrine (Correct Answer)
- B. Dopamine
- C. Acetylcholine
- D. Epinephrine
Explanation: ***Norepinephrine*** - **Norepinephrine** is the primary neurotransmitter released by **postganglionic sympathetic neurons** directly onto the heart to increase heart rate and contractility in response to a drop in blood pressure. - It acts on **beta-1 adrenergic receptors** in the sinoatrial (SA) node, atria, and ventricles, leading to increased chronotropy (heart rate) and inotropy (contractility). *Dopamine* - While **dopamine** can have cardiovascular effects, particularly at high doses, it is not the primary neurotransmitter released by the sympathetic nervous system for direct heart rate regulation. - Dopamine is a precursor to norepinephrine and epinephrine, but its main physiological roles involve **renal blood flow regulation** and central nervous system functions. *Acetylcholine* - **Acetylcholine** is the primary neurotransmitter of the **parasympathetic nervous system**, which generally acts to **decrease heart rate** (bradycardia) through muscarinic receptors. - It is also released by **preganglionic sympathetic fibers**, but these do not directly innervate the heart to produce the desired effect of increasing heart rate. *Epinephrine* - **Epinephrine** (adrenaline) is primarily a **hormone** released from the **adrenal medulla** into the bloodstream, not directly from postganglionic sympathetic nerve terminals to the heart. - Although it has strong effects on beta-1 receptors in the heart, its release is more generalized and slower than the direct neuronal release of norepinephrine.
Question 5: Which of the following statements best describes the mechanism of action of insulin on target cells?
- A. Insulin binds to a receptor on the outer surface of the plasma membrane, activating adenylate cyclase through the Gs protein.
- B. Insulin binds to a cytoplasmic receptor and is transferred as a hormone receptor complex to the nucleus to modulate gene expression.
- C. Insulin enters the cell and causes the release of calcium ions from intracellular stores.
- D. Insulin binds to a transmembrane receptor on the outer surface of the plasma membrane, activating the tyrosine kinase in the cytosolic domain of the receptor. (Correct Answer)
Explanation: ***Insulin binds to a transmembrane receptor on the outer surface of the plasma membrane, activating the tyrosine kinase in the cytosolic domain of the receptor.*** - **Insulin** is a **peptide hormone** and cannot freely pass through the lipid bilayer, thus it binds to a **transmembrane receptor** on the cell surface. - This binding leads to the activation of the receptor's intrinsic **tyrosine kinase activity** in the intracellular domain, initiating a signaling cascade. *Insulin binds to a cytoplasmic receptor and is transferred as a hormone receptor complex to the nucleus to modulate gene expression.* - This mechanism describes the action of **steroid hormones**, which are lipid-soluble and can cross the cell membrane, binding to **intracellular receptors**. - **Insulin** acts via a **cell surface receptor** and its downstream effects are mediated through signal transduction pathways, not direct nuclear translocation. *Insulin binds to a receptor on the outer surface of the plasma membrane, activating adenylate cyclase through the Gs protein.* - This mechanism is characteristic of **G-protein coupled receptors (GPCRs)**, which activate or inhibit enzymes like adenylate cyclase via G-proteins to produce second messengers like cyclic AMP. - The **insulin receptor** is a **receptor tyrosine kinase**, not a GPCR, and does not directly activate adenylate cyclase via Gs protein. *Insulin enters the cell and causes the release of calcium ions from intracellular stores.* - While some hormones and neurotransmitters can trigger the release of intracellular **calcium ions**, this is typically mediated by specific pathways (e.g., GPCRs linked to phospholipase C). - **Insulin** does not directly enter target cells to cause calcium release; its actions are primarily mediated through receptor tyrosine kinase signaling pathways.
Question 6: Which of the following binds to intracellular receptors?
- A. Growth hormone
- B. Vitamin E
- C. Estrogen (Correct Answer)
- D. Insulin
Explanation: ***Estrogen*** - **Estrogen** is a **steroid hormone** that, due to its **lipophilic nature**, can easily pass through the cell membrane to bind to **intracellular receptors** in the cytoplasm or nucleus. - This binding leads to the formation of a **hormone-receptor complex** that acts as a transcription factor, regulating **gene expression**. *Growth hormone* - **Growth hormone** is a **peptide hormone** and therefore **hydrophilic**, meaning it cannot freely cross the cell membrane. - It binds to **transmembrane receptors** on the cell surface, initiating intracellular signaling cascades through pathways like the **JAK/STAT pathway**. *Vitamin E* - **Vitamin E** is a **lipid-soluble vitamin** and an important **antioxidant**, but it does not function as a signaling molecule that binds to intracellular receptors to regulate gene expression in the same manner as steroid hormones. - While it diffuses across membranes due to its lipophilicity, its primary role is to protect cell membranes from **oxidative damage**. *Insulin* - **Insulin** is a **protein hormone** that is **hydrophilic** and cannot pass through the cell membrane. - It binds to **tyrosine kinase receptors** on the cell surface, triggering a cascade of intracellular events like the **PI3K/Akt pathway** to regulate glucose metabolism.
Question 7: Cell-to-cell permeability occurs through
- A. Connexins (Correct Answer)
- B. Occludin
- C. Zona adherens
- D. Zonulin
Explanation: ***Connexins*** - **Connexins** are the proteins that form **gap junctions**, which are specialized intercellular channels that allow direct passage of ions and small molecules between adjacent cells. - These channels facilitate **cell-to-cell communication** and regulate permeability by enabling the rapid exchange of electrical and chemical signals. *Occludin* - **Occludin** is a key protein component of **tight junctions** (zona occludens), which are primarily responsible for sealing the space between cells and preventing paracellular leakage. - Tight junctions **restrict cell-to-cell permeability** rather than promoting it, defining tissue polarity. *Zona adherens* - The **zona adherens** (adherens junctions) are cell junctions that provide strong **mechanical attachment** between cells through the binding of adjacent cell membranes. - They are involved in maintaining tissue integrity and cell shape but do not directly regulate **cell-to-cell permeability** of substances. *Zonulin* - **Zonulin** is a protein that modulates **intestinal tight junction permeability**, acting as a regulator of the paracellular pathway. - While it affects permeability, it does so by *loosening tight junctions*, not by forming direct cell-to-cell channels that allow substance passage.
Question 8: Which of the following statements accurately describes G proteins?
- A. Are associated with cellular membranes and play a crucial role in signal transduction. (Correct Answer)
- B. Regulate second messengers like cyclic adenosine monophosphate (cAMP).
- C. Play a role in the amplification of hormonal signals.
- D. Consist of three subunits: alpha, beta, and gamma.
Explanation: ***Are associated with cellular membranes and play a crucial role in signal transduction.*** - **G proteins** are critical components of **G protein-coupled receptors (GPCRs)**, which are embedded in the **cellular membrane**. - They act as molecular switches, relaying signals from diverse extracellular stimuli (like hormones, neurotransmitters, and light) across the cell membrane into the cell's interior, thus initiating a **signal transduction pathway**. - This is the most comprehensive and accurate description of G proteins as a whole. *Regulate second messengers like cyclic adenosine monophosphate (cAMP).* - While G proteins do regulate second messengers such as **cAMP** by activating enzymes like **adenylyl cyclase**, this describes a **specific mechanism of action**, not a broad description of what G proteins are. - This statement is accurate but too narrow, describing one particular function rather than their fundamental role in membrane association and general signal transduction. *Play a role in the amplification of hormonal signals.* - G proteins are involved in signal transduction pathways that can lead to **signal amplification**, but this is a **downstream effect**, not their primary defining characteristic. - Mentioning their role only in amplification of hormonal signals is too narrow and doesn't capture their fundamental nature as signal transducers. *Consist of three subunits: alpha, beta, and gamma.* - This statement accurately describes **heterotrimeric G proteins** (the most common type involved in GPCR signaling), which do have three subunits (Gα, Gβ, Gγ). - However, this is **incorrect as a general description** because there are also **monomeric G proteins** (small GTPases like Ras, Rho, Rac, and Rab) that consist of a single polypeptide chain. - Since the question asks about "G proteins" in general without specifying heterotrimeric G proteins, this statement is incomplete and therefore incorrect.
Question 9: Prokaryotes do not have
- A. Ribosome
- B. Cell wall
- C. Cell membrane
- D. Mitochondria (Correct Answer)
Explanation: ***Mitochondria*** - Prokaryotic cells **lack membrane-bound organelles**, including mitochondria. - Cellular respiration in prokaryotes occurs in the **cytoplasm** and on the **cell membrane**. *Ribosome* - Ribosomes are essential for **protein synthesis** and are present in both prokaryotic and eukaryotic cells. - Prokaryotic ribosomes are generally **smaller (70S)** than eukaryotic ribosomes (80S). *Cell wall* - Many prokaryotes, particularly bacteria, possess a **cell wall** for structural support and protection. - This structure is typically composed of **peptidoglycan** in bacteria. *Cell membrane* - A **cell membrane** is a fundamental component of all living cells, including prokaryotes, controlling passage of substances. - It plays a crucial role in **energy production** and signaling in prokaryotic cells.
Question 10: Which of the following is a major component of the plasma membrane?
- A. Protein
- B. Carbohydrate
- C. Cholesterol
- D. Phospholipid (Correct Answer)
Explanation: ***Phospholipid*** - **Phospholipids** form the fundamental **phospholipid bilayer** structure of the plasma membrane, acting as a barrier. - Their **amphipathic nature** (hydrophilic head and hydrophobic tails) allows them to spontaneously form this bilayer in an aqueous environment. *Carbohydrate* - **Carbohydrates** are present on the outer surface of the plasma membrane, forming the **glycocalyx**, but are not a major structural component of the bilayer itself. - They primarily function in **cell recognition** and adhesion. *Protein* - **Proteins** are embedded within or associated with the phospholipid bilayer, facilitating various functions like **transport**, signaling, and adhesion. - While crucial for function, they do not form the basic structural framework of the membrane. *Cholesterol* - **Cholesterol** is a type of lipid that helps regulate the **fluidity** and stability of the plasma membrane. - It is interspersed within the phospholipid bilayer but is not the primary structural component.
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