Q.1 What is the primary function of a second messenger in a cell?
Transcribing DNA
Transporting oxygen
Relaying signals inside the cell
Breaking down proteins
Explanation - Second messengers, such as cyclic AMP, propagate signals from cell surface receptors to internal targets.
Correct answer is: Relaying signals inside the cell
Q.2 Which molecule acts as a ligand for the epidermal growth factor receptor (EGFR)?
Insulin
Epidermal Growth Factor
Glucose
Acetylcholine
Explanation - EGF binds to EGFR, triggering receptor dimerization and activation of downstream signaling pathways.
Correct answer is: Epidermal Growth Factor
Q.3 What does the term 'phosphorylation' refer to in cellular signaling?
Adding a phosphate group to a protein
Removing a protein from a cell
Breaking a DNA strand
Adding a sugar to a lipid
Explanation - Phosphorylation typically activates or deactivates proteins, regulating signaling cascades.
Correct answer is: Adding a phosphate group to a protein
Q.4 Which ion is crucial for initiating action potentials in neurons?
Calcium
Sodium
Potassium
Magnesium
Explanation - Sodium influx depolarizes the membrane, triggering the action potential.
Correct answer is: Sodium
Q.5 A signaling pathway that uses cGMP as a second messenger is most commonly associated with:
Vision
Hormone secretion
Blood clotting
Muscle contraction
Explanation - cGMP mediates light detection in rod cells of the retina.
Correct answer is: Vision
Q.6 Which of the following is a classic example of autocrine signaling?
Insulin secreted by beta cells acting on the liver
Growth hormone acting on muscle cells
Epidermal growth factor acting on the same cell that produced it
Neuropeptide released into the synaptic cleft
Explanation - Autocrine signaling means the cell responds to its own secreted signals.
Correct answer is: Epidermal growth factor acting on the same cell that produced it
Q.7 Which protein is directly downstream of G-protein activation in the cAMP pathway?
Protein kinase A
CaMKII
MAPK
Phospholipase C
Explanation - Activated Gs increases cAMP, which activates PKA to phosphorylate target proteins.
Correct answer is: Protein kinase A
Q.8 The JAK-STAT pathway is typically activated by signals that:
Inhibit cyclic AMP production
Activate tyrosine kinases
Increase intracellular calcium
Depolymerize actin filaments
Explanation - Cytokine binding activates JAK, which phosphorylates STAT transcription factors.
Correct answer is: Activate tyrosine kinases
Q.9 Which of the following describes a paracrine signal?
Signal travels through the bloodstream to distant organs
Signal acts on the cell that produced it
Signal affects nearby neighboring cells
Signal is released into the synaptic cleft
Explanation - Paracrine signals influence cells in close proximity to the secreting cell.
Correct answer is: Signal affects nearby neighboring cells
Q.10 Which kinase is directly activated by diacylglycerol (DAG) and calcium?
Protein kinase A
Protein kinase C
Tyrosine kinase
Serine/threonine kinase
Explanation - PKC requires DAG and Ca²⁺ for membrane association and activation.
Correct answer is: Protein kinase C
Q.11 A mutation that prevents the addition of phosphate groups to a receptor tyrosine kinase would most likely:
Increase receptor activity
Decrease receptor activity
Have no effect on receptor activity
Change the receptor's ligand specificity
Explanation - Phosphorylation of RTKs is essential for full activation of downstream pathways.
Correct answer is: Decrease receptor activity
Q.12 What is the role of phospholipase C in Gq-coupled receptor signaling?
Generate cAMP from ATP
Produce IP3 and DAG from PIP2
Add phosphate groups to proteins
Transport calcium ions across the membrane
Explanation - PLC hydrolyzes PIP2, producing IP3 and DAG that trigger downstream events.
Correct answer is: Produce IP3 and DAG from PIP2
Q.13 Which of the following best describes an endocrine signal?
Signal that travels across a synaptic cleft
Signal released into the bloodstream to reach distant cells
Signal affecting only the cell that produced it
Signal that requires direct cell-cell contact
Explanation - Endocrine signals travel via blood to act on cells far away from the source.
Correct answer is: Signal released into the bloodstream to reach distant cells
Q.14 Which molecule is a key component of the extracellular matrix that binds growth factors?
Collagen
Fibronectin
Hyaluronic acid
Heparan sulfate proteoglycans
Explanation - These proteoglycans bind and modulate growth factor distribution and signaling.
Correct answer is: Heparan sulfate proteoglycans
Q.15 What is the main function of the MAPK/ERK signaling cascade?
Initiate apoptosis
Control cell proliferation and differentiation
Transport molecules across the nuclear envelope
Regulate ion channel opening
Explanation - MAPK/ERK transmits mitogenic signals from the membrane to the nucleus.
Correct answer is: Control cell proliferation and differentiation
Q.16 Which neurotransmitter is primarily released from cholinergic neurons at the neuromuscular junction?
Dopamine
Glutamate
Acetylcholine
Serotonin
Explanation - Acetylcholine mediates muscle contraction by binding nicotinic receptors.
Correct answer is: Acetylcholine
Q.17 A Gs protein-coupled receptor increases levels of which second messenger?
cAMP
IP3
DAG
Ca²⁺
Explanation - Gs stimulates adenylyl cyclase to convert ATP to cAMP.
Correct answer is: cAMP
Q.18 Which protein is activated by binding to both DAG and increased intracellular calcium?
CaMKII
PKA
PKC
CREB
Explanation - Protein kinase C requires both DAG and Ca²⁺ for full activation.
Correct answer is: PKC
Q.19 In the Notch signaling pathway, the ligand is typically a:
Soluble hormone
Membrane-bound protein
Ion channel
Cytoplasmic enzyme
Explanation - Notch ligands such as Delta are presented on adjacent cell surfaces.
Correct answer is: Membrane-bound protein
Q.20 Which of these is NOT a common method for measuring intracellular calcium levels?
Fluorescent calcium indicators
Luminescence-based dyes
Electron microscopy
Fluorescence microscopy
Explanation - Calcium levels are typically measured with fluorescent or luminescent dyes, not EM.
Correct answer is: Electron microscopy
Q.21 Which of the following best describes the role of cGMP-dependent protein kinase (PKG)?
Phosphorylates phospholipids
Degrades cGMP
Phosphorylates target proteins in response to cGMP
Transports cGMP across membranes
Explanation - PKG is activated by cGMP and phosphorylates downstream effectors.
Correct answer is: Phosphorylates target proteins in response to cGMP
Q.22 What is the primary role of the second messenger IP3?
Activate protein kinase A
Release calcium from the endoplasmic reticulum
Produce cyclic GMP
Inhibit phospholipase C
Explanation - IP3 binds to its receptor on the ER, opening calcium channels.
Correct answer is: Release calcium from the endoplasmic reticulum
Q.23 The term 'signal transduction' refers to:
Transport of signals across the synapse
Conversion of extracellular signals into cellular responses
Electrical conduction in nerves
Physical transduction of light
Explanation - Signal transduction is the process of transmitting a signal from outside to inside the cell.
Correct answer is: Conversion of extracellular signals into cellular responses
Q.24 Which molecule serves as a major energy currency and is required for ATP synthesis in mitochondria?
Glucose
Oxygen
NADH
Cytokine
Explanation - NADH donates electrons to the electron transport chain, driving ATP synthesis.
Correct answer is: NADH
Q.25 In the context of cell signaling, a 'ligand' is:
A receptor protein
An intracellular enzyme
A molecule that binds to a receptor
A cell membrane lipid
Explanation - Ligands can be hormones, neurotransmitters, or growth factors that activate receptors.
Correct answer is: A molecule that binds to a receptor
Q.26 Which of the following describes the effect of a Gq protein on adenylyl cyclase?
Stimulation
Inhibition
No effect
Degradation
Explanation - Gq typically activates phospholipase C, not adenylyl cyclase, which is mainly influenced by Gs or Gi.
Correct answer is: Inhibition
Q.27 Which receptor type is directly coupled to the opening of ion channels?
G-protein-coupled receptors
Receptor tyrosine kinases
Ligand-gated ion channels
Cytokine receptors
Explanation - Ligand-gated ion channels change conformation to allow ion flow upon ligand binding.
Correct answer is: Ligand-gated ion channels
Q.28 In the Hedgehog signaling pathway, the intracellular protein that translocates to the nucleus is:
Sonic Hedgehog
Smoothened
Gli
Patched
Explanation - Gli proteins act as transcription factors activated downstream of Hedgehog signaling.
Correct answer is: Gli
Q.29 Which of the following best explains 'ligand-receptor specificity'?
The ability of a ligand to cross the cell membrane
The exclusive interaction between a specific ligand and its receptor
The capacity of a receptor to bind all types of ligands
The speed at which a ligand binds to a receptor
Explanation - Ligand-receptor specificity ensures correct cellular responses to signaling molecules.
Correct answer is: The exclusive interaction between a specific ligand and its receptor
Q.30 Which protein is commonly phosphorylated by PKA as part of the cAMP pathway?
CREB
PKC
MAPK
Phospholipase C
Explanation - CREB is a transcription factor phosphorylated by PKA, activating gene expression.
Correct answer is: CREB
Q.31 Which of the following best characterizes 'signal amplification' in a signaling pathway?
One signal molecule activates many downstream molecules
The signal strength is reduced as it propagates
The signal is amplified by the cell membrane
Signal amplification requires two receptors
Explanation - Signal amplification allows a single ligand to trigger a robust cellular response.
Correct answer is: One signal molecule activates many downstream molecules
Q.32 What role does the protein Ras play in cell signaling?
It acts as a second messenger
It is a GTPase that activates MAPK pathways
It transports calcium across membranes
It degrades cyclic AMP
Explanation - Ras switches between GTP-bound active and GDP-bound inactive states, regulating downstream cascades.
Correct answer is: It is a GTPase that activates MAPK pathways
Q.33 Which of the following is a characteristic of a chemotactic signaling molecule?
It attracts cells toward its source
It repels cells from its source
It is only found intracellularly
It binds to DNA directly
Explanation - Chemotactic signals guide cell migration by creating a concentration gradient.
Correct answer is: It attracts cells toward its source
Q.34 The term 'phosphatidylinositol 3-kinase' (PI3K) refers to an enzyme that:
Adds a phosphate to PIP2 producing PIP3
Adds a phosphate to PIP3 producing PIP2
Removes phosphate groups from phospholipids
Phosphorylates proteins
Explanation - PI3K phosphorylates PIP2 to generate PIP3, a key lipid second messenger.
Correct answer is: Adds a phosphate to PIP2 producing PIP3
Q.35 Which receptor type is primarily involved in immune signaling and is activated by cytokines?
Receptor tyrosine kinases
Cytokine receptors
G-protein-coupled receptors
Ion channels
Explanation - Cytokine receptors bind signaling proteins like interleukins and interferons.
Correct answer is: Cytokine receptors
Q.36 A key feature of the Wnt signaling pathway is the:
Direct activation of adenylate cyclase
Stabilization of β-catenin in the cytoplasm
Inhibition of MAPK
Phosphorylation of phospholipase C
Explanation - Wnt signaling prevents β-catenin degradation, allowing it to enter the nucleus.
Correct answer is: Stabilization of β-catenin in the cytoplasm
Q.37 Which of the following is an example of a neurotransmitter that functions as an autocrine signal?
Glutamate
Acetylcholine
Serotonin
None of the above
Explanation - Neurotransmitters generally act paracrine or synaptic, not autocrine.
Correct answer is: None of the above
Q.38 Which of these molecules is NOT a typical second messenger?
cAMP
cGMP
IP3
ATP
Explanation - ATP is a primary energy currency, not a classical second messenger.
Correct answer is: ATP
Q.39 Which protein is the downstream effector of the phosphoinositide 3-kinase pathway that leads to cell survival?
Akt (Protein kinase B)
MAPK
Raf
JNK
Explanation - Akt is activated downstream of PI3K and promotes cell survival and growth.
Correct answer is: Akt (Protein kinase B)
Q.40 The 'receptor tyrosine kinase' family primarily functions by:
Binding small ions
Phosphorylating extracellular domains
Autophosphorylating tyrosine residues
Opening ligand-gated ion channels
Explanation - RTKs autophosphorylate upon ligand binding, initiating downstream signaling.
Correct answer is: Autophosphorylating tyrosine residues
Q.41 In the context of cell signaling, a 'decoy receptor' is one that:
Amplifies the signal
Binds ligands without triggering signaling
Degrades the ligand
Inhibits ligand synthesis
Explanation - Decoy receptors sequester ligands, reducing signaling intensity.
Correct answer is: Binds ligands without triggering signaling
Q.42 Which of the following is a key role of the extracellular matrix (ECM) in tissue engineering?
Providing electrical conduction
Acting as a scaffold for cell growth
Translating mechanical signals
All of the above
Explanation - ECM supports cell attachment, provides electrical cues, and transmits mechanical forces.
Correct answer is: All of the above
Q.43 Which ion is predominantly involved in the initiation of action potentials in muscle cells?
Sodium
Potassium
Calcium
Chloride
Explanation - Calcium influx triggers muscle contraction in skeletal and cardiac muscle.
Correct answer is: Calcium
Q.44 The 'G12/13' family of G proteins primarily influences:
cAMP production
Cytoskeletal dynamics
Calcium release
Ion channel opening
Explanation - G12/13 modulates Rho GTPases, affecting the actin cytoskeleton.
Correct answer is: Cytoskeletal dynamics
Q.45 Which of the following best describes the role of a 'receptor tyrosine kinase' in embryonic development?
Facilitating cell movement by degrading the ECM
Providing structural support to developing tissues
Regulating cell proliferation and differentiation via signaling cascades
Transporting oxygen to embryonic cells
Explanation - RTKs are critical for interpreting growth factor signals during development.
Correct answer is: Regulating cell proliferation and differentiation via signaling cascades
Q.46 What is the primary effect of increased intracellular calcium concentration on the contractile apparatus?
Inhibits myosin ATPase activity
Promotes cross-bridge formation between actin and myosin
Decreases actin polymerization
Inhibits phospholipase C
Explanation - Calcium binds troponin, enabling actin-myosin interactions in muscle contraction.
Correct answer is: Promotes cross-bridge formation between actin and myosin
Q.47 Which of the following is an example of a paracrine signal in the nervous system?
Glutamate released into the synaptic cleft
Neuropeptide Y acting on nearby neurons
Insulin acting on muscle cells
Acetylcholine acting on the diaphragm
Explanation - Paracrine signals affect neighboring cells rather than distant targets.
Correct answer is: Neuropeptide Y acting on nearby neurons
Q.48 Which of the following enzymes hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) to produce IP3 and DAG?
Phospholipase D
Phospholipase A2
Phospholipase C
Phospholipase B
Explanation - PLC cleaves PIP2 into the second messengers IP3 and DAG.
Correct answer is: Phospholipase C
Q.49 In a typical MAPK cascade, which kinase directly phosphorylates the next kinase in the sequence?
MAPK
MAPKK
MAPKKK
Raf
Explanation - MAPKKK phosphorylates MAPKK, which in turn phosphorylates MAPK.
Correct answer is: MAPKKK
Q.50 Which of these molecules is NOT typically involved in the classic cAMP signaling pathway?
Adenylyl cyclase
Protein kinase A
Phospholipase C
Exchange protein directly activated by cAMP (Epac)
Explanation - PLC is part of the Gq pathway, not the canonical cAMP cascade.
Correct answer is: Phospholipase C
Q.51 Which of the following best describes the 'ligand-binding domain' of a receptor?
The region that anchors the receptor to the membrane
The intracellular portion that initiates signaling
The extracellular portion that binds the ligand
The site where the receptor degrades the ligand
Explanation - The ligand-binding domain is typically located outside the cell membrane.
Correct answer is: The extracellular portion that binds the ligand
Q.52 What is the primary role of the 'smoothened' protein in Hedgehog signaling?
Act as a receptor for Sonic Hedgehog
Transmit the signal inside the cell by being activated when Patched is inhibited
Degrade Hedgehog ligands
Serve as a transcription factor
Explanation - Smoothened becomes active when Patched is removed, allowing downstream signaling.
Correct answer is: Transmit the signal inside the cell by being activated when Patched is inhibited
Q.53 Which of the following best illustrates the concept of 'signal integration' in a cell?
A single ligand activating multiple receptors
Multiple signaling pathways converging on a single transcription factor
The breakdown of a signal molecule by a phosphatase
The activation of a G-protein by a ligand
Explanation - Signal integration involves combining inputs from various pathways to produce a coordinated response.
Correct answer is: Multiple signaling pathways converging on a single transcription factor
Q.54 Which of the following is a characteristic of a hormone acting via an intracellular receptor?
It is typically polar
It crosses the plasma membrane
It binds to a membrane-bound GPCR
It is degraded by the proteasome
Explanation - Lipophilic hormones can diffuse through the membrane and bind intracellular receptors.
Correct answer is: It crosses the plasma membrane
Q.55 What is the primary function of the scaffold protein in signal transduction?
To degrade signaling molecules
To bring signaling components into close proximity
To act as a second messenger
To inhibit receptor activation
Explanation - Scaffold proteins organize signaling complexes, ensuring specificity and efficiency.
Correct answer is: To bring signaling components into close proximity
Q.56 Which of these pathways directly leads to the phosphorylation of transcription factor Elk-1?
cAMP-PKA
MAPK/ERK
PI3K-Akt
JAK-STAT
Explanation - Elk-1 is phosphorylated by ERK, a key MAPK pathway component.
Correct answer is: MAPK/ERK
Q.57 The term 'phosphorylation cascade' refers to:
The sequential addition of phosphate groups to a single protein
The chain of phosphorylation events involving multiple enzymes
The breakdown of a phospholipid into second messengers
The inhibition of protein kinases
Explanation - It describes a series of kinase-mediated phosphorylation steps transmitting signals.
Correct answer is: The chain of phosphorylation events involving multiple enzymes
Q.58 In the context of cell signaling, what does the term 'receptor desensitization' mean?
The receptor becomes permanently active
The receptor is internalized and degraded
The receptor stops responding to ligand stimulation
The receptor is upregulated at the cell surface
Explanation - Desensitization reduces receptor responsiveness after prolonged exposure to ligand.
Correct answer is: The receptor stops responding to ligand stimulation
Q.59 Which of the following is a characteristic of the Gq protein signaling pathway?
Activation of adenylyl cyclase
Stimulation of phospholipase C
Inhibition of MAPK
Direct activation of protein kinase C
Explanation - Gq activates PLC, leading to production of IP3 and DAG.
Correct answer is: Stimulation of phospholipase C
Q.60 Which of the following molecules is NOT a direct target of protein kinase A?
CREB
Phospholipase C
Ion channels
Transcription factors
Explanation - PKA mainly targets transcription factors and ion channels, not PLC.
Correct answer is: Phospholipase C
Q.61 What is the consequence of a loss-of-function mutation in the PTEN gene?
Reduced cell proliferation
Increased cell death
Hyperactivation of the PI3K/Akt pathway
Decreased PI3K activity
Explanation - PTEN dephosphorylates PIP3; its loss leads to unchecked PI3K signaling.
Correct answer is: Hyperactivation of the PI3K/Akt pathway
Q.62 Which of the following is an example of a cytokine?
Insulin
Interleukin-2
Epinephrine
Melatonin
Explanation - IL-2 is a cytokine involved in T-cell proliferation.
Correct answer is: Interleukin-2
Q.63 Which of the following best describes the role of the 'synaptic cleft'?
An intracellular compartment storing neurotransmitters
A gap between the presynaptic and postsynaptic membranes
A region of the neuron that degrades neurotransmitters
A structure that forms the axon initial segment
Explanation - Neurotransmitters diffuse across this cleft to bind receptors.
Correct answer is: A gap between the presynaptic and postsynaptic membranes
Q.64 Which of these is a hallmark of GPCR activation?
Direct phosphorylation of downstream targets
Binding of GTP to Gα subunit
Ligand-independent activation
Direct DNA binding
Explanation - GPCR activation triggers GDP-GTP exchange on Gα.
Correct answer is: Binding of GTP to Gα subunit
Q.65 Which of the following best characterizes the 'Janus kinase' (JAK) in cell signaling?
A cytoskeletal protein
A protein that dephosphorylates STAT
A receptor tyrosine kinase
A cytoplasmic tyrosine kinase activated by cytokine receptors
Explanation - JAKs associate with cytokine receptors to phosphorylate STATs.
Correct answer is: A cytoplasmic tyrosine kinase activated by cytokine receptors
Q.66 In the context of cell signaling, the term 'second messenger' refers to:
A protein that directly binds to receptors
A small molecule that relays signals within the cell
A large polymer that transports ions
A cytokine secreted by the cell
Explanation - Second messengers such as cAMP, IP3, and calcium propagate signals intracellularly.
Correct answer is: A small molecule that relays signals within the cell
Q.67 Which of the following signaling proteins directly binds to the phosphotyrosine residues on activated receptors?
Src family kinases
Grb2
Ras
STAT
Explanation - Src kinases recognize phosphotyrosine via SH2 domains, initiating downstream cascades.
Correct answer is: Src family kinases
Q.68 Which of the following describes the role of 'caveolae' in cell signaling?
They act as storage sites for calcium ions
They serve as membrane domains that concentrate signaling molecules
They degrade signaling proteins
They are cytoplasmic organelles for protein folding
Explanation - Caveolae are flask-shaped invaginations rich in signaling receptors.
Correct answer is: They serve as membrane domains that concentrate signaling molecules
Q.69 The 'Toll-like receptor' (TLR) family is primarily involved in:
Regulating circadian rhythms
Detecting pathogen-associated molecular patterns
Sensing mechanical stretch
Transmitting synaptic signals
Explanation - TLRs recognize microbial components to trigger innate immunity.
Correct answer is: Detecting pathogen-associated molecular patterns
Q.70 Which of the following is an example of a 'negative feedback loop' in cell signaling?
Activation of a kinase that in turn activates the same kinase
Production of a transcription factor that upregulates its own gene
Activation of a phosphatase that dephosphorylates the activating kinase
Binding of a ligand to a receptor that increases ligand production
Explanation - Negative feedback reduces the activity of a signaling component.
Correct answer is: Activation of a phosphatase that dephosphorylates the activating kinase
Q.71 Which of the following best describes the role of 'phospholipase D' in cell signaling?
Phosphorylates the plasma membrane
Generates diacylglycerol and inositol 1,4,5-trisphosphate
Hydrolyzes phosphatidic acid to produce phosphatidic acid
Hydrolyzes phosphatidylcholine to produce phosphatidic acid
Explanation - PLD cleaves phosphatidylcholine to yield phosphatidic acid and choline.
Correct answer is: Hydrolyzes phosphatidylcholine to produce phosphatidic acid
Q.72 Which of the following is NOT a typical function of a transcription factor in signal transduction?
Binding to DNA to regulate gene expression
Phosphorylating other proteins
Translocating to the nucleus
Being activated by upstream kinases
Explanation - Transcription factors mainly regulate gene expression, not kinase activity.
Correct answer is: Phosphorylating other proteins
Q.73 Which of the following is a direct downstream target of the PI3K-Akt pathway?
Glycogen synthase kinase 3 (GSK-3)
ERK
PKC
Phospholipase C
Explanation - Akt phosphorylates and inhibits GSK-3, affecting glycogen synthesis.
Correct answer is: Glycogen synthase kinase 3 (GSK-3)
Q.74 The 'Rho family GTPases' primarily regulate:
DNA replication
Actin cytoskeleton dynamics
Microtubule stability
Protein synthesis
Explanation - Rho GTPases control actin polymerization and cell shape.
Correct answer is: Actin cytoskeleton dynamics
Q.75 In cell signaling, the term 'crosstalk' refers to:
The physical crossing of two receptors
The interaction between two or more signaling pathways
The cross-linking of DNA strands
The crossing of a signal from one cell to another across a synapse
Explanation - Crosstalk can modify or integrate multiple signaling outputs.
Correct answer is: The interaction between two or more signaling pathways
Q.76 Which of the following is an example of a 'synthetic agonist'?
Insulin
Glucose
Albuterol
Adrenaline
Explanation - Albuterol is a synthetic drug that activates β2-adrenergic receptors.
Correct answer is: Albuterol
Q.77 Which of the following best describes a 'phosphatase'?
An enzyme that adds phosphate groups to proteins
An enzyme that removes phosphate groups from proteins
A receptor that binds phospholipids
A transcription factor that binds DNA
Explanation - Phosphatases dephosphorylate proteins, often counteracting kinases.
Correct answer is: An enzyme that removes phosphate groups from proteins
Q.78 Which of the following is a primary effect of increased cyclic GMP levels in vascular smooth muscle cells?
Vasoconstriction
Vasodilation
Increased intracellular calcium
Activation of MAPK
Explanation - cGMP activates PKG, leading to smooth muscle relaxation and vasodilation.
Correct answer is: Vasodilation
Q.79 The 'cAMP response element-binding protein' (CREB) is activated by:
Phosphorylation by protein kinase A
Binding to cyclic GMP
Phosphorylation by protein kinase C
Binding to calcium
Explanation - CREB is phosphorylated by PKA, allowing it to bind DNA and activate transcription.
Correct answer is: Phosphorylation by protein kinase A
Q.80 Which of the following best characterizes the role of 'growth factor receptors' in cell signaling?
They are primarily involved in neurotransmission
They bind soluble growth factors and activate intracellular signaling cascades
They act as ion channels
They degrade extracellular matrix components
Explanation - Growth factor receptors initiate signaling pathways controlling proliferation and differentiation.
Correct answer is: They bind soluble growth factors and activate intracellular signaling cascades
Q.81 Which of the following is a feature of the 'TGF-β' signaling pathway?
Involves ligand binding to a receptor tyrosine kinase
Uses SMAD proteins as intracellular signal transducers
Relies on cyclic AMP as a second messenger
Activates G-proteins directly
Explanation - TGF-β signaling uses SMAD transcription factors for gene regulation.
Correct answer is: Uses SMAD proteins as intracellular signal transducers
Q.82 Which of these molecules is commonly used in experiments to inhibit protein kinase C?
H-89
Bisindolylmaleimide I
U0126
PD98059
Explanation - Bisindolylmaleimide I is a selective PKC inhibitor.
Correct answer is: Bisindolylmaleimide I
Q.83 What is the primary role of the 'cAMP response element' (CRE) in gene regulation?
It acts as a promoter for all genes
It is a DNA sequence that binds CREB to regulate transcription
It codes for a protein kinase
It is a membrane receptor
Explanation - CRE elements are promoter sequences that respond to phosphorylated CREB.
Correct answer is: It is a DNA sequence that binds CREB to regulate transcription
Q.84 Which of the following best describes the role of 'adenylate cyclase' in the cAMP signaling pathway?
It degrades cAMP into AMP
It generates cAMP from ATP
It phosphorylates CREB
It transports ATP across membranes
Explanation - Adenylate cyclase converts ATP to cyclic AMP in response to GPCR activation.
Correct answer is: It generates cAMP from ATP
Q.85 The 'Ras' protein is primarily involved in:
Phosphorylating tyrosine residues on receptors
Binding to GTP and activating downstream MAPK cascade
Transporting calcium ions
Synthesis of cAMP
Explanation - Ras is a small GTPase that initiates the MAPK signaling pathway.
Correct answer is: Binding to GTP and activating downstream MAPK cascade
Q.86 Which of the following is a major function of the 'phosphoinositide 3-kinase' (PI3K) pathway?
Inhibiting cell growth
Promoting cell survival and proliferation
Activating MAPK cascade
Degrading extracellular matrix
Explanation - PI3K-Akt signaling promotes survival and growth by phosphorylating downstream targets.
Correct answer is: Promoting cell survival and proliferation
Q.87 Which of the following best describes the role of the 'Wnt' signaling pathway?
Regulating calcium homeostasis in bone
Controlling cell proliferation and differentiation via β-catenin
Activating the cAMP-PKA pathway
Inhibiting the MAPK cascade
Explanation - Wnt signals prevent β-catenin degradation, allowing it to activate target genes.
Correct answer is: Controlling cell proliferation and differentiation via β-catenin
Q.88 Which of the following molecules serves as a 'primary messenger' in endocrine signaling?
cAMP
IP3
Insulin
Calcium
Explanation - Primary messengers are the hormones or ligands that directly bind to receptors.
Correct answer is: Insulin
Q.89 Which of the following best characterizes the role of a 'scaffold protein' in the MAPK cascade?
It phosphorylates MAPK directly
It brings kinases into close proximity for efficient signaling
It degrades MAPK to terminate signaling
It translocates MAPK into the nucleus
Explanation - Scaffold proteins organize signaling modules to enhance specificity and efficiency.
Correct answer is: It brings kinases into close proximity for efficient signaling
Q.90 Which of the following is NOT a function of 'cytokine receptors'?
Binding interleukins
Activating JAK-STAT signaling
Directly transporting ions across the membrane
Mediating inflammatory responses
Explanation - Cytokine receptors typically signal via JAK-STAT, not as ion channels.
Correct answer is: Directly transporting ions across the membrane
Q.91 Which of the following best describes the role of 'phospholipase C' (PLC) in Gq signaling?
It generates IP3 and DAG from PIP2
It produces cyclic AMP from ATP
It phosphorylates proteins directly
It transports calcium ions into the cytosol
Explanation - PLC cleaves PIP2 to produce IP3, which releases calcium, and DAG, which activates PKC.
Correct answer is: It generates IP3 and DAG from PIP2
Q.92 Which of the following best characterizes the role of 'protein kinase A' (PKA) in the cAMP pathway?
It degrades cAMP into AMP
It is activated by cAMP and phosphorylates target proteins
It transports cAMP across the plasma membrane
It directly binds to DNA
Explanation - PKA is a cAMP-dependent serine/threonine kinase that phosphorylates downstream targets.
Correct answer is: It is activated by cAMP and phosphorylates target proteins
Q.93 Which of the following best describes the function of the 'MAPK' cascade?
Regulates ion transport in the plasma membrane
Transmits signals from the cell surface to the nucleus
Degrades extracellular matrix
Binds to DNA to activate transcription directly
Explanation - MAPK cascades relay signals from receptors to nuclear transcription factors.
Correct answer is: Transmits signals from the cell surface to the nucleus
Q.94 Which of the following molecules is a key component of the 'second messenger' system in many cells?
Cytokine
Cyclic GMP
Insulin
Neurotransmitter
Explanation - Cyclic GMP is a second messenger that modulates various cellular processes.
Correct answer is: Cyclic GMP
Q.95 Which of the following best describes the role of the 'cGMP-dependent protein kinase' (PKG)?
It phosphorylates G-proteins directly
It degrades cGMP
It is activated by cGMP and phosphorylates target proteins
It transports cGMP out of the cell
Explanation - PKG is a cGMP-dependent serine/threonine kinase that modulates downstream targets.
Correct answer is: It is activated by cGMP and phosphorylates target proteins
Q.96 Which of the following best describes the role of 'protein phosphatase 2A' (PP2A)?
Adds phosphate groups to proteins
Removes phosphate groups from serine/threonine residues
Adds phosphate groups to tyrosine residues
Transports proteins across the nuclear envelope
Explanation - PP2A is a major serine/threonine phosphatase that counteracts kinase activity.
Correct answer is: Removes phosphate groups from serine/threonine residues
Q.97 Which of the following best characterizes the 'Gq' signaling pathway?
It activates adenylyl cyclase
It stimulates phospholipase C
It inhibits phospholipase C
It directly activates protein kinase A
Explanation - Gq-coupled receptors stimulate PLC to produce IP3 and DAG.
Correct answer is: It stimulates phospholipase C
Q.98 Which of the following best describes the function of the 'smoothened' protein in Hedgehog signaling?
It binds Hedgehog ligand directly
It is inhibited by Patched when Hedgehog is absent
It acts as a transcription factor
It degrades Hedgehog ligand
Explanation - Smoothened is normally suppressed by Patched; Hedgehog binding releases this inhibition.
Correct answer is: It is inhibited by Patched when Hedgehog is absent
Q.99 Which of the following is a key role of 'integrin-mediated signaling'?
Transmitting electrical signals across the synaptic cleft
Providing mechanical attachment and transmitting signals from the extracellular matrix
Regulating gene transcription directly
Degrading proteins in the cytoplasm
Explanation - Integrins connect the ECM to the cytoskeleton and activate intracellular signaling pathways.
Correct answer is: Providing mechanical attachment and transmitting signals from the extracellular matrix
Q.100 Which of the following best describes the role of 'cytokines' in immune signaling?
They act as hormones regulating metabolism
They are soluble proteins that mediate communication between immune cells
They are enzymes that degrade bacterial cell walls
They function as ion channels in immune cells
Explanation - Cytokines coordinate immune responses by signaling between cells.
Correct answer is: They are soluble proteins that mediate communication between immune cells
Q.101 Which of the following best characterizes the 'JNK' signaling pathway?
It is involved in stress responses and apoptosis
It activates cAMP production
It promotes cell survival by inhibiting apoptosis
It is primarily found in plant cells
Explanation - JNK is a MAPK that responds to stress stimuli and can trigger apoptosis.
Correct answer is: It is involved in stress responses and apoptosis
Q.102 Which of the following best describes the role of 'G-protein coupled receptors' (GPCRs)?
They are ion channels that allow ion passage
They bind hormones and activate G-proteins to relay signals inside cells
They degrade second messengers
They are transcription factors that bind DNA
Explanation - GPCRs detect extracellular signals and activate heterotrimeric G proteins.
Correct answer is: They bind hormones and activate G-proteins to relay signals inside cells
Q.103 Which of the following best describes the role of 'phosphatidylinositol 3-kinase' (PI3K) in cellular signaling?
It generates cAMP from ATP
It phosphorylates PIP2 to produce PIP3, activating Akt
It directly phosphorylates DNA
It degrades extracellular matrix components
Explanation - PI3K converts PIP2 to PIP3, initiating the Akt survival pathway.
Correct answer is: It phosphorylates PIP2 to produce PIP3, activating Akt
Q.104 Which of the following best describes the role of 'protein kinase C' (PKC)?
It degrades cyclic AMP
It is activated by DAG and calcium to phosphorylate target proteins
It transports calcium ions into the nucleus
It synthesizes ATP
Explanation - PKC is a serine/threonine kinase activated by DAG and calcium.
Correct answer is: It is activated by DAG and calcium to phosphorylate target proteins
Q.105 Which of the following molecules is a key mediator of the 'cAMP' signaling pathway?
Calmodulin
CREB
IP3
DAG
Explanation - CREB is a transcription factor phosphorylated by PKA, a downstream effector of cAMP.
Correct answer is: CREB
Q.106 Which of the following best describes the role of 'JAK-STAT' signaling?
It involves DNA repair mechanisms
It transduces cytokine signals from the cell surface to the nucleus
It is responsible for neurotransmitter release
It degrades extracellular matrix proteins
Explanation - JAK phosphorylates STAT, which then dimerizes and enters the nucleus to regulate genes.
Correct answer is: It transduces cytokine signals from the cell surface to the nucleus
Q.107 Which of the following best characterizes the role of 'phospholipase D' (PLD)?
It breaks down phosphatidylcholine to produce phosphatidic acid
It synthesizes phosphatidylinositol 4,5-bisphosphate
It is a second messenger
It is a membrane transporter for cAMP
Explanation - PLD hydrolyzes phosphatidylcholine to generate phosphatidic acid and choline.
Correct answer is: It breaks down phosphatidylcholine to produce phosphatidic acid
Q.108 Which of the following best describes the role of the 'integrin' family of proteins?
They function as hormone receptors
They mediate cell adhesion to the extracellular matrix
They are ion channels that transport calcium
They synthesize cAMP
Explanation - Integrins are transmembrane receptors that connect ECM to the cytoskeleton.
Correct answer is: They mediate cell adhesion to the extracellular matrix
Q.109 Which of the following molecules is a key regulator of the 'MAPK' cascade?
Raf
cAMP
DAG
Calcium
Explanation - Raf is a MAPKKK that initiates the MAPK signaling cascade.
Correct answer is: Raf
Q.110 Which of the following best describes the role of 'cyclic AMP' (cAMP) in cellular signaling?
It is an ion channel
It is a second messenger that activates PKA
It directly binds DNA
It is a primary messenger that binds to receptors
Explanation - cAMP is produced by adenylyl cyclase and activates PKA to phosphorylate targets.
Correct answer is: It is a second messenger that activates PKA
Q.111 Which of the following is an example of a 'negative feedback regulator' in a signaling pathway?
A receptor that phosphorylates its own ligand
A phosphatase that dephosphorylates an active kinase
A G-protein that activates itself continuously
A ligand that binds irreversibly to the receptor
Explanation - Phosphatases remove phosphate groups, thereby turning off signaling.
Correct answer is: A phosphatase that dephosphorylates an active kinase
Q.112 Which of the following best characterizes the 'Wnt/β-catenin' signaling pathway?
It relies on cAMP as a second messenger
It stabilizes β-catenin to promote gene transcription
It directly activates MAPK
It is activated by calcium influx
Explanation - Wnt signaling prevents β-catenin degradation, allowing it to enter the nucleus.
Correct answer is: It stabilizes β-catenin to promote gene transcription
Q.113 Which of the following best describes the role of the 'Rho family GTPases'?
They phosphorylate tyrosine residues
They regulate the actin cytoskeleton dynamics
They act as second messengers
They synthesize extracellular matrix proteins
Explanation - Rho GTPases control actin polymerization and cell shape.
Correct answer is: They regulate the actin cytoskeleton dynamics
Q.114 Which of the following best describes the function of 'heparan sulfate proteoglycans' in the extracellular matrix?
They act as enzymes that degrade collagen
They bind and present growth factors to their receptors
They are ion channels embedded in the membrane
They produce ATP for the cell
Explanation - These proteoglycans sequester growth factors and regulate their availability.
Correct answer is: They bind and present growth factors to their receptors
Q.115 Which of the following best describes the role of 'cGMP' in vascular smooth muscle cells?
It increases intracellular calcium levels
It activates PKG leading to muscle relaxation
It degrades phospholipase C
It binds to DNA to activate gene transcription
Explanation - cGMP activates PKG, which relaxes smooth muscle, causing vasodilation.
Correct answer is: It activates PKG leading to muscle relaxation
Q.116 Which of the following is an example of a 'synthetic antagonist' used in research?
Insulin
Angiotensin II
Nimodipine
Serotonin
Explanation - Nimodipine is a synthetic drug that blocks L-type calcium channels.
Correct answer is: Nimodipine
Q.117 Which of the following best describes the role of 'protein kinase B' (Akt) in cellular signaling?
It phosphorylates histones directly
It promotes cell survival and metabolism by phosphorylating downstream targets
It inhibits MAPK activation
It degrades extracellular matrix proteins
Explanation - Akt is a central node in PI3K signaling, regulating growth, survival, and metabolism.
Correct answer is: It promotes cell survival and metabolism by phosphorylating downstream targets
Q.118 Which of the following is a primary function of the 'Ras' protein?
It adds a phosphate group to proteins
It binds to GTP and activates downstream signaling pathways
It transports calcium ions into the nucleus
It degrades extracellular matrix proteins
Explanation - Ras is a small GTPase that initiates MAPK and other pathways.
Correct answer is: It binds to GTP and activates downstream signaling pathways
Q.119 Which of the following best describes the function of 'Toll-like receptors' (TLRs)?
They detect microbial molecules and activate innate immunity
They transport calcium across the plasma membrane
They generate cAMP from ATP
They bind directly to DNA
Explanation - TLRs recognize pathogen-associated molecular patterns to trigger immune responses.
Correct answer is: They detect microbial molecules and activate innate immunity
Q.120 Which of the following best characterizes the role of 'cytokine receptors' in cell signaling?
They are primarily involved in neuronal signaling
They bind cytokines and activate JAK-STAT signaling
They directly transport calcium into the cell
They are ion channels that open in response to voltage changes
Explanation - Cytokine receptors are critical for immune cell communication via JAK-STAT.
Correct answer is: They bind cytokines and activate JAK-STAT signaling