Cell Signaling and Communication
Signal Transduction
Communication pathways
Cells communicate using hormones, neurotransmitters, growth factors, and local signals. A signaling pathway typically includes reception, transduction, and response.
Core pathway logic
One signal can trigger many downstream molecules, allowing amplification and precise regulation.
Receptors and second messengers
Cell-surface receptors often use second messengers such as or . Intracellular receptors bind small hydrophobic ligands that can cross membranes, such as steroid hormones.
Why are many peptide hormones unable to cross the plasma membrane?
Polar, large molecules usually require membrane receptors rather than diffusing through the lipid bilayer.
Correct answer: They are generally polar and large
What is signal amplification?
Amplification allows small signals to trigger strong responses.
Correct answer: A single activated receptor can lead to activation of many downstream molecules and a large cellular response.
Interpreting pathway experiments
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1
Identify the ligand, receptor, and response being measured.
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2
Determine whether the effect is blocked at reception or downstream transduction.
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3
Check whether second messenger levels change.
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4
Infer where the mutation or inhibitor acts in the pathway.
Which molecule often acts as a second messenger in signaling pathways?
cAMP is a classic second messenger that relays and amplifies signals inside cells.
Correct answer: cAMP