Lecture 16-17
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What two roles can cells serve in signaling?
Cells can act as signaling cells that produce extracellular signaling molecules, and as target cells that contain receptors that specifically recognize and respond to those signals.
Define signal transduction.
Process where one type of signal is converted into another; begins when a receptor receives an extracellular signal and generates intracellular signaling molecules that alter cell behavior.
What does ‘cell signaling’ include?
All mechanisms of signal reception and signal transduction.
How does a cell determine which signals to respond to?
By the limited set of receptors it expresses; different receptors detect different signals.
Can the same signal molecule produce different responses?
Yes—different cells may express different receptors or have different intracellular signaling responses.
What makes a cellular response fast vs slow?
Fast responses modify existing proteins; slow responses require gene expression and synthesis of new proteins.
Examples of fast cellular responses?
Changes in cell movement, secretion, or metabolism (seconds to minutes).
Examples of slow cellular responses?
Cell growth, division, or differentiation (hours).
Two classes of extracellular signaling molecules?
Large/hydrophilic (bind cell-surface receptors) and small/hydrophobic molecules (diffuse into cell and bind intracellular receptors).
Types of chemicals that act as signaling molecules?
Proteins, peptides, amino acids, nucleotides, steroids, fatty acid derivatives, and dissolved gases.
Endocrine signaling definition.
Long-distance signaling where hormones travel through bloodstream to distant target cells.
Example signaling molecule in endocrine signaling.
Insulin secreted by pancreas.
Paracrine signaling definition.
Local signaling through diffusion in extracellular fluid; affects nearby cells.
Examples of paracrine signaling molecules.
Cytokines and interferons involved in inflammation or wound repair.
Autocrine signaling definition.
Cells respond to signaling molecules they secrete themselves.
Example of autocrine signaling.
Cancer cells producing growth and survival signals for themselves.
Neuronal signaling definition.
Electrical signals travel along neurons; neurotransmitters released at synapses for cell-to-cell signaling.
Examples of neurotransmitters.
Glutamine, aspartate, D-serine.
Contact-dependent signaling definition.
Requires direct physical contact; signaling molecule remains membrane-bound and binds receptor on adjacent cell.
Contact-dependent signaling example.
Delta–Notch signaling during embryonic development enabling adjacent cells to adopt different identities.
Role of receptor protein in signaling.
Performs the primary transduction step—receives external signal and generates intracellular signal responses.
How do intracellular signaling pathways function?
Like a relay race—signal is passed from one molecule to another.
Functions of intracellular signaling pathways.
Relay, amplify, integrate, and distribute the signal; also enable feedback modulation.
What are molecular switches?
Proteins activated/inactivated by phosphorylation or by GTP binding.