AP Syllabus focus:
‘Signal transduction can change gene expression and cell function, producing new phenotypes or altering existing cellular activities.’
Cells respond to signals by converting information at receptors into specific molecular changes. These changes can be fast and reversible or slower and longer-lasting, depending on whether gene expression is altered.
What a “cellular response” means
A signal transduction pathway ends when effector molecules produce a measurable change in the target cell, such as altered enzyme activity, secretion, movement, or transcription.
Cellular response: The specific change in a cell’s activity caused by a signal transduction pathway, often through altered protein function and/or gene expression.
Practice Questions
FAQ
Different cells express different transcription factors and co-regulators.
A signal-activated factor may recruit activators in one cell type but repressors in another.
Reversible responses usually rely on protein-state changes and stop when the signal is removed.
Persistent responses often involve altered transcription and stable protein-level shifts.
They may be activated by conformational change or phosphorylation.
They may also translocate into the nucleus to access DNA regulatory sequences.
Receptor inactivation or internalisation
Deactivation of relay proteins (e.g. by phosphatases)
Degradation or removal of the signalling molecule
Cells combine inputs through shared relay proteins and converging transcriptional control.
The final output reflects the balance of activating and inhibitory pathway activity.
