Complete Exam Guide Subject-wise practice platform
0 XP
Biochemistry and Molecular Biology

Cell Signalling and Receptors Practice Questions

22 free Cell Signalling and Receptors practice questions for the USMLE Step 1. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

Practice in Quiz Mode

Question 1 of 22 Medium

Which structural feature is diagnostic of a G-protein–coupled receptor (GPCR)?

  1. A A single transmembrane α-helix
  2. B Seven transmembrane α-helices
  3. C A cytosolic DNA-binding domain
  4. D A ligand-gated ion pore composed of multiple subunits

Correct answer: Seven transmembrane α-helices

GPCRs are defined by their seven transmembrane α-helices, which allow them to transmit extracellular signals via G proteins.

Question 2 of 22 Medium

Activation of a receptor tyrosine kinase (RTK) most directly causes:

  1. A Opening of a plasma-membrane channel for Ca²⁺ influx
  2. B Exchange of bound GDP for GTP on a heterotrimeric G protein
  3. C Autophosphorylation of the receptor's tyrosine residues
  4. D Translocation of the intact receptor into the cell nucleus

Correct answer: Autophosphorylation of the receptor's tyrosine residues

Ligand binding to an RTK induces receptor dimerization and autophosphorylation of its intracellular tyrosine residues, initiating downstream signaling.

Question 3 of 22 Medium

Which second messenger is most closely associated with a GPCR linked to Gα_s activation?

  1. A cAMP
  2. B IP₃
  3. C DAG
  4. D cGMP

Correct answer: cAMP

Gα_s stimulates adenylate cyclase, which increases cyclic AMP (cAMP), a key second messenger in many GPCR-mediated pathways.

Question 4 of 22 Medium

A receptor that directly opens an ion channel in response to ligand binding is best classified as:

  1. A G-protein–coupled receptor (metabotropic type)
  2. B Enzyme-linked (catalytic) receptor
  3. C Ligand-gated ion channel receptor
  4. D Intracellular nuclear hormone receptor

Correct answer: Ligand-gated ion channel receptor

Ligand-gated ion channels (ionotropic receptors) open in response to ligand binding, allowing ions to pass through the membrane; they are distinct from GPCRs and enzyme-linked receptors.

Question 5 of 22 Medium

Which type of receptor typically mediates effects of lipid-soluble hormones (e.g., steroid hormones)?

  1. A G-protein–coupled receptor (metabotropic)
  2. B Ligand-gated ion channel receptor
  3. C Enzyme-linked catalytic receptor
  4. D Intracellular (nuclear) receptor

Correct answer: Intracellular (nuclear) receptor

Lipid-soluble hormones diffuse across the membrane and bind intracellular (nuclear) receptors, which then often act as transcription factors to regulate gene expression.

Question 6 of 22 Medium

Upon ligand binding to a GPCR, what occurs next in the G-protein activation cycle?

  1. A The receptor turns into a tyrosine kinase and autophosphorylates itself
  2. B GDP on the Gα subunit is replaced by GTP, and Gα separates from βγ
  3. C The receptor is immediately internalized before any signal is transmitted
  4. D The ligand–receptor complex moves directly into the cell nucleus

Correct answer: GDP on the Gα subunit is replaced by GTP, and Gα separates from βγ

Ligand binding to GPCR triggers GDP-to-GTP exchange on Gα, causing it to dissociate from the βγ complex; both can then activate downstream effectors.

Question 7 of 22 Medium

Which of the following is NOT one of the three major classes of cell-surface receptors involved in signal transduction?

  1. A G-protein–coupled receptors (GPCRs)
  2. B Ligand-gated ion channels
  3. C Enzyme-linked receptors
  4. D Mitochondrial inner-membrane receptors

Correct answer: Mitochondrial inner-membrane receptors

The three canonical cell-surface receptor classes are GPCRs, ligand-gated ion channels, and enzyme-linked receptors; mitochondrial inner-membrane receptors are not a standard category.

Question 8 of 22 Medium

Activation of an RTK can lead to a Ras → Raf → MEK → ERK cascade. What is the primary biological consequence of this cascade?

  1. A Rapid flux of ions across the plasma membrane
  2. B Immediate depolarization of the cell membrane
  3. C Signal amplification that alters gene expression or cell behavior
  4. D Termination of GPCR signaling within the same cell

Correct answer: Signal amplification that alters gene expression or cell behavior

RTK activation triggers kinase cascades (e.g., MAP kinase pathway) that amplify the signal and often result in changes in gene expression, cell proliferation, or differentiation.

Question 9 of 22 Medium

Why can a very low concentration of a signaling ligand elicit a large cellular response?

  1. A Because the ligand binds permanently and irreversibly to its receptors
  2. B Because each individual receptor binds many ligand molecules at once
  3. C Because transduction amplifies signal via second messengers and kinase cascades
  4. D Because the ligands enter the nucleus to directly switch on many genes

Correct answer: Because transduction amplifies signal via second messengers and kinase cascades

Signal amplification allows even a few ligand-receptor interactions to generate many second messengers or activate multiple downstream enzymes, leading to large cellular responses.

Question 10 of 22 Medium

What is a common mechanism for terminating signaling from many cell-surface receptors after ligand binding?

  1. A Permanent and irreversible inactivation of every cell receptor
  2. B Immediate enzymatic destruction of the ligand in the extracellular space
  3. C Endocytosis of the ligand–receptor complex, then ligand breakdown or recycling
  4. D Phosphorylation of the extracellular domain to block further ligand binding

Correct answer: Endocytosis of the ligand–receptor complex, then ligand breakdown or recycling

Receptor internalization (endocytosis) removes ligand–receptor complexes from the cell surface; ligand is degraded and receptor may be recycled or degraded, terminating the signal.

Question 11 of 22 Medium

A water-soluble peptide hormone that acts through a cell-surface receptor most likely uses which signaling mechanism?

  1. A Diffusion across the membrane to bind cytoplasmic nuclear receptors
  2. B Binding a cell-surface receptor that triggers a second-messenger cascade
  3. C Direct entry into the nucleus to modulate gene transcription
  4. D Insertion into the membrane to form a ligand-gated ion channel

Correct answer: Binding a cell-surface receptor that triggers a second-messenger cascade

Hydrophilic peptide hormones cannot cross the lipid bilayer, so they bind to cell-surface receptors (GPCRs or enzyme-linked) and activate intracellular second messenger pathways.

Question 12 of 22 Medium

Which G protein α-subunit family typically activates phospholipase C, leading to generation of IP₃ and DAG?

  1. A Gα_s
  2. B Gα_i
  3. C Gα_q/11
  4. D Gα_12/13

Correct answer: Gα_q/11

Gα_q family subunits activate phospholipase C, which cleaves PIP₂ into IP₃ and DAG; IP₃ then mobilizes Ca²⁺ from intracellular stores and DAG activates protein kinase C.

Question 13 of 22 Medium

Which receptor class is most likely to mediate rapid synaptic transmission in neurons via direct ion flow upon neurotransmitter binding?

  1. A GPCR
  2. B Enzyme-linked receptor
  3. C Ligand-gated ion channel
  4. D Intracellular nuclear receptor

Correct answer: Ligand-gated ion channel

Ligand-gated ion channels open upon neurotransmitter binding, allowing rapid ion movement across membranes — suitable for fast synaptic signaling.

Question 14 of 22 Medium

Intracellular (nuclear) receptors differ from cell-surface receptors primarily because:

  1. A They bind only proteins, whereas cell-surface receptors bind small molecules
  2. B After ligand binding they enter the nucleus and directly regulate gene transcription
  3. C They always trigger immediate cellular changes through rapid ion flux
  4. D They lack any functional ligand-binding domain of their own

Correct answer: After ligand binding they enter the nucleus and directly regulate gene transcription

Nuclear receptors bind hydrophobic ligands that diffuse into the cell; upon activation they move to the nucleus and act as transcription regulators — unlike cell-surface receptors that use second messengers or ion flow.

Question 15 of 22 Medium

Which of these describes a common feature of enzyme-linked receptors (like RTKs)?

  1. A Seven membrane-spanning transmembrane alpha-helical domains
  2. B An intrinsic or associated intracellular catalytic (enzymatic) domain
  3. C Formation of a ligand-gated transmembrane ion pore on binding
  4. D Perpetual irreversible activation once the ligand is bound

Correct answer: An intrinsic or associated intracellular catalytic (enzymatic) domain

Enzyme-linked receptors carry or recruit enzymatic activity — often a kinase — in their intracellular domain; ligand binding activates this catalytic function to initiate downstream signaling.

Question 16 of 22 Medium

If a mutation prevented GTP hydrolysis by a Gα subunit in a GPCR pathway, what would be the most likely result?

  1. A Complete failure to activate any downstream effector molecules
  2. B Prolonged, sustained activation of downstream signaling
  3. C Immediate internalization and degradation of the receptor
  4. D No measurable effect on the duration of signaling

Correct answer: Prolonged, sustained activation of downstream signaling

Without GTP hydrolysis, the Gα subunit remains in its active GTP-bound state, continuously stimulating downstream effectors and prolonging the signal.

Question 17 of 22 Medium

Which receptor type is most likely to directly influence intracellular Ca²⁺ levels by mobilizing Ca²⁺ from endoplasmic reticulum stores?

  1. A A GPCR coupled to Gα_q that activates phospholipase C
  2. B An RTK triggering the Ras/MAPK kinase cascade pathway
  3. C A ligand-gated sodium channel mediating membrane depolarization
  4. D An intracellular nuclear receptor regulating gene transcription

Correct answer: A GPCR coupled to Gα_q that activates phospholipase C

GPCRs coupled to Gα_q activate phospholipase C, generating IP₃ which binds to ER receptors and causes Ca²⁺ release — a common route to mobilize intracellular Ca²⁺.

Question 18 of 22 Medium

A growth factor binds to its receptor on a target cell. Subsequently, the receptor dimerizes and phosphorylates itself. Which downstream effect is most consistent with this mechanism?

  1. A Rapid Na⁺ influx producing immediate membrane depolarization
  2. B cAMP-mediated activation of protein kinase A (PKA)
  3. C A phosphorylation cascade that alters gene expression
  4. D Immediate opening of a membrane chloride (Cl⁻) channel

Correct answer: A phosphorylation cascade that alters gene expression

Growth factor receptors are often RTKs; their autophosphorylation initiates kinase cascades (e.g. MAPK) that lead to changes in gene expression and cell behavior.

Question 19 of 22 Medium

Which scenario best illustrates signal amplification in cell signaling?

  1. A One ligand binds one receptor and opens a single ion channel briefly
  2. B One ligand–receptor event generates many second messengers that activate many effectors
  3. C One receptor permanently binds its ligand, locking the signal on
  4. D Each receptor reliably triggers only a single downstream molecule

Correct answer: One ligand–receptor event generates many second messengers that activate many effectors

Signal amplification occurs when a single ligand–receptor interaction triggers generation of many second messengers or activates many downstream proteins, magnifying the initial signal.

Question 20 of 22 Medium

Which of these receptor mechanisms typically results in the fastest cellular response (milliseconds)?

  1. A GPCR signaling via cAMP
  2. B RTK-mediated kinase cascade
  3. C Ligand-gated ion channel opening
  4. D Nuclear receptor–mediated gene transcription

Correct answer: Ligand-gated ion channel opening

Ligand-gated ion channels open almost immediately upon ligand binding, allowing ion flux that leads to rapid responses — much faster than second messenger or transcription-mediated pathways.

Question 21 of 22 Medium

Which of the following best distinguishes metabotropic receptors from ionotropic receptors?

  1. A Metabotropic receptors open ion channels directly; ionotropic ones do not
  2. B Metabotropic receptors act via G proteins; ionotropic directly gate ion flow
  3. C Metabotropic receptors are intracellular; ionotropic are on the cell surface
  4. D Metabotropic receptors always activate kinases; ionotropic always block ions

Correct answer: Metabotropic receptors act via G proteins; ionotropic directly gate ion flow

Metabotropic receptors (such as GPCRs) signal via G proteins and second messengers, indirectly affecting cell physiology; ionotropic receptors directly open ion channels on ligand binding to regulate ion flow.

Question 22 of 22 Medium

Which receptor type is least likely to involve a multi-step intracellular cascade before eliciting a cellular response?

  1. A Receptor tyrosine kinase (RTK) signaling
  2. B Gα_s-coupled GPCR raising cAMP levels
  3. C A ligand-gated ion channel gating ion flow directly
  4. D A GPCR coupled to phospholipase C signaling

Correct answer: A ligand-gated ion channel gating ion flow directly

Ligand-gated ion channels directly allow ion flow upon ligand binding, eliciting rapid responses without extensive intracellular signaling cascades.

0 / 22 answered