Read the notes, then try the practice. It adapts as you go.When you're ready.
Session Length
~17 min
Adaptive Checks
15 questions
Transfer Probes
8
Cell communication is the process by which cells detect and respond to signals from their environment and from other cells. In multicellular organisms, coordinated cell signaling is essential for growth, immune defense, tissue repair, and homeostasis. The three stages of cell signaling -- reception, transduction, and response -- allow cells to convert extracellular chemical signals into specific intracellular actions such as changes in gene expression, enzyme activity, or cell shape.
Signal transduction pathways amplify and relay messages from the cell surface to the nucleus or cytoplasm. Ligands bind to receptor proteins (G protein-coupled receptors, receptor tyrosine kinases, or intracellular receptors), triggering cascades of phosphorylation events, second messengers such as cyclic AMP and calcium ions, and ultimately cellular responses. Feedback mechanisms -- both positive and negative -- regulate these pathways to maintain appropriate signal strength and duration.
The cell cycle is the ordered sequence of events by which a cell duplicates its contents and divides. It consists of interphase (G1, S, and G2 phases) and the mitotic phase (mitosis and cytokinesis). Critical checkpoints at G1, G2, and the metaphase-to-anaphase transition ensure that DNA is intact, fully replicated, and properly aligned before the cell proceeds. Cyclins and cyclin-dependent kinases (CDKs) are the molecular drivers of cell cycle progression. When checkpoint controls fail -- through mutations in proto-oncogenes or tumor suppressor genes such as p53 -- cells can proliferate uncontrollably, leading to cancer.
One step at a time.
The process by which a cell converts an extracellular signal into a specific intracellular response through receptor activation, relay molecules, and second messengers.
Example: When epinephrine binds to a GPCR on a liver cell, a cascade involving G proteins, adenylyl cyclase, cAMP, and protein kinase A triggers glycogen breakdown.
A large family of cell-surface receptors with seven transmembrane domains that activate G proteins when a ligand binds, which then activate downstream enzymes or ion channels.
Example: The beta-adrenergic receptor in heart cells responds to epinephrine, increasing heart rate through cAMP.
Cell-surface receptors that dimerize and autophosphorylate tyrosine residues upon ligand binding, creating docking sites for relay proteins.
Example: The EGF receptor triggers the Ras-MAPK pathway to promote cell growth.
Small molecules (cAMP, Ca2+, IP3) that relay and amplify signals from receptors to targets inside the cell.
Example: One receptor can generate thousands of cAMP molecules -- this is signal amplification.
Regulatory points (G1, G2, metaphase) where the cell checks DNA integrity, replication, and spindle attachment before proceeding.
Example: At G1, p53 activates repair genes or triggers apoptosis if DNA damage is detected.
Cyclins fluctuate during the cell cycle; CDKs, when cyclin-bound, phosphorylate targets to drive cell cycle progression.
Example: Cyclin D binds CDK4, phosphorylating Rb to release E2F and allow S phase entry.
Programmed cell death via caspase activation, DNA fragmentation, and membrane blebbing without inflammation.
Example: During embryonic development, apoptosis removes webbing between fingers and toes.
Choose a different way to engage with this topic — no grading, just richer thinking.
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See how the key ideas connect. Nodes color in as you practice.
Walk through a solved problem step-by-step. Try predicting each step before revealing it.
This is guided practice, not just a quiz. Hints and pacing adjust in real time.
Small steps add up.
What you get while practicing:
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