BIO230H1 Lecture Notes - Lecture 4: Signal Transduction, Scaffold Protein, Isogamy
Lecture Seven: Principles of Cellular Signaling
Cellular Signaling:
• Cells must communicate to develop and maintain multicellular organisms
• Unicellular bacterial-like organisms existed on earth for ~2.5 billion years before complex
multicellular organisms
Unicellular Communication:
• Many bacteria release and respond to chemical signals
o This signaling coordinates motility,
antibiotic production, spore formation
and sexual conjugation in bacterial populations
Mating in Budding Yeasts:
• Signaling between yeast cells
prepares them to mate
o Single-celled eukaryotes
Aggregation of Ameboid Cells:
• Signaling between dictyostelium cells draws
them together to form a fruiting body
o Dictyostelium is a slime mold
o Fruiting body – pile on top of each other to increase spore dispersal
The Basics of Sending and Receiving Signals:
• Cells can send out hundreds of different types of signaling molecules
o Ex. proteins, small peptides, amino acids, nucleotides, small molecules, gases
• They are exocytosed from the cell, emitted by diffusion, displayed on the cell surface
Cells Receive Signals in Two Main Ways:
1. Cell–Surface Receptors
• Signal molecule
(typically hydrophilic)
binds to receptors on the
surface of the cell
2. Intracellular Receptors
• Receptors are in the inside
of the cell (nucleus, cytosol)
• Signal molecule
(typically hydrophobic)
requires carrier protein
to transport it inside the cell
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Signaling Occurring Over Short Distances:
1. Contact–Dependent Signaling
• Signals are retained on the
cell surface
• Fast over short distances
2. Paracrine Signaling
• Signals are released from the cell
but act locally
• Signal movement is restricted by:
o Internalization by neighboring cells
o Signal instability or destruction by extracellular enzymes
o Binding to extracellular matric molecules
• Slightly longer distances – and takes slightly longer time
Signaling Occurring Over Long Distances:
1. Synaptic Signaling
• Neurons extend axons to contact
distant target cells
• The released signaling molecules
act locally at target
• Fast over long distances
2. Endocrine Signaling
• Endocrine cells secrete hormones into the bloodstream for long-range distribution
• Short over long distances
Cells Use Signal Transduction Pathways to Respond to Extracellular Signals:
Signal Transduction:
• The conversion of extracellular signals
into intracellular signals
Effector:
• A downstream molecule in a signal
transduction pathway
(upstream molecules have their
own effects on them)
o Upstream: before
triangle is upstream of circle
o Downstream: after
triangle is downstream of cube
Signal affect receptor which then affects
the different proteins which affect other
proteins and then the cell will react
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Intracellular signaling:
1. Small Intracellular Signaling Molecules:
o Known as second messengers
o Made in large number and diffuse through
the cytoplasm (ex. cAMP) or plasma
membrane (ex. diacylglycerol)
o Bind and alter effector molecules
2. Large Intracellular Signaling Molecules:
o Typically, proteins
o Organized into pathways and
networks
Components of a Signal Transduction Pathways:
*hypothetical pathway
*not all pathways work like this – it can be different
*not all the pathways have all the possible parts
*some proteins may have multiple functions
Scaffold:
• Draws multiple signaling components together
to increase efficiency and specificity
Relay:
• Sends the signal downstream in the basic form
(Ex. Protein–protein interactions)
Transduce and Amplify:
• Converts the signal into a different form
(Ex. an enzyme making a small molecule or
phosphorylating downstream proteins)
• Amplifying the signal by performing many conversions
Integration:
• Requires inputs from two or more pathways to
send the signal (a coincidence detector)
Spread:
• Sends the signal to other pathways
(increases the complexity of the response)
(activates more than one protein)
Anchor:
• Restricts the location of the signaling
(recruitment to a subcellular compartment)
Modulate:
• Restricts the intensity of the signaling
(down-regulation/stops the signal)
find more resources at oneclass.com
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BIO230H1 Full Course Notes
Verified Note
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Document Summary
Cellular signaling: cells must communicate to develop and maintain multicellular organisms, unicellular bacterial-like organisms existed on earth for ~2. 5 billion years before complex multicellular organisms. Unicellular communication: many bacteria release and respond to chemical signals, this signaling coordinates motility, antibiotic production, spore formation and sexual conjugation in bacterial populations. Mating in budding yeasts: signaling between yeast cells prepares them to mate, single-celled eukaryotes. Aggregation of ameboid cells: signaling between dictyostelium cells draws them together to form a fruiting body, dictyostelium is a slime mold, fruiting body pile on top of each other to increase spore dispersal. Cells use signal transduction pathways to respond to extracellular signals: Signal transduction: the conversion of extracellular signals into intracellular signals. Effector: a downstream molecule in a signal transduction pathway (upstream molecules have their own effects on them, upstream: before triangle is upstream of circle, downstream: after triangle is downstream of cube.
