BI110 Lecture Notes - Lecture 25: Signal Transduction, Platelet-Derived Growth Factor, Growth Factor
BI110 Lecture 25 (Wednesday, November 15th) – Cell Signaling Continued
Recall: Steps in Cell Signaling
• Signal does not have to be in a high concentration to get a response (ex. hormones normally act
in very low concentrations)
• Receptor activation signal molecule specifically bound by receptor – makes the receptor
activated (similar to an allosteric activator that changes shape of receptor and activating it)
o Receptor is like an enzyme
• Signal transduction cascade: receptor does something to another molecule to turn it on – chain
reaction
• Response: lots of different responses – turning genes on/off, manipulating
transcription/translation
• Response termination – very important, cell only wants to respond when signal is present, so
cell must be able to turn response off when signal is not present
o Multiple steps must occur to turn off response
o Activated enzyme must become inactivated
o Must unbind signal from receptor (just turning off the enzyme is not enough)
▪ Reversible – triggers the receptor to be constantly switching between
active/inactive forms
• Strength and duration of response affected by:
o Binding affinity of signal to receptor
▪ Different receptors have different affinities for their signals (high affinity = more
often active, low affinity = more often inactive)
o Concentration of termination enzymes
o Concentration of signal transduction components
o Concentration of signal itself
▪ Higher concentration of signal = more receptors bound to signal and becoming
activated
▪ However, concentration is always relative to its starting point
• Ex. going from a concentration of zero to a low concentration could be
considered a great change (ex. adrenaline is a hormone when found in
small amounts can create a large effect)
Signaling over long and short distances
• Endocrine
• Paracrine
• Autocrine
• Contact-dependent signaling
Endocrine Signaling
• Endocrine signaling – Signal travels large distances
through the circulatory system (bloodstream)
• Some signaling molecules may need to travel great
distances in the body through the circulatory system.
• Ex. hormones – estrogen and testosterone travel
through body from where they are made
Paracrine Signaling
• Paracrine signaling involves two cells that are close to each other.
• In paracrine signaling, the signal is usually a small, soluble molecule
o Ex. growth factors
• Signal produced by one cell, secreted and then sensed by another cell
o Could be occurring in tissues of one organ
Document Summary
Bi110 lecture 25 (wednesday, november 15th) cell signaling continued. Signaling over long and short distances: endocrine, paracrine, autocrine, contact-dependent signaling. Paracrine signaling: paracrine signaling involves two cells that are close to each other. In paracrine signaling, the signal is usually a small, soluble molecule: ex. growth factors, signal produced by one cell, secreted and then sensed by another cell, could be occurring in tissues of one organ. Autocrine signaling: autocrine signaling occurs when the signaling cell and the responding cell are one and the same, quorum sensing type of autocrine signaling. Cell contact dependent signaling: contact-dependent signaling occurs in the absence of a signaling molecule. Signaling molecule and receptor: reversible receptor can go back and forth between active and inactive. Cell surface receptors: polar signaling molecules cannot cross the plasma membrane and rely on cell-surface receptors, polar molecules cannot get inside cell on their own, protein in plasma membrane has parts inside and outside of the cell.
