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Cell Signaling
Types of Cell Signaling
• No Distance:
1. Gap junctions
2. Plasmodesmata
• Local
1. Paracrine Signaling: secreting cell acts on nearby target cells
2. Synaptic Signaling: nerve cell releases NT’s to adjacent nerve cells
• Long distance
1. Endocrine signaling: endocrine cells release hormones into blood
stream, affecting cells in other parts of the body
Three Stages of Cell Signaling
1. Reception: ligand binds to receptor protein
2. Transduction: multistep process that amplifies signal
3. Response: usually turns genes on/off or alters a protein’s activity
Reception
Types of signal receptors:
1. Receptors in plasma membrane
G Protein Coupled Receptor (GPCR)
Ligand-gated ion channel
2. Intracellular receptors
Reception
Binding of ligand
to a GPCR
activates a G
protein which
leaves the GPCR,
diffuses across the
membrane, and
activates an
enzyme which
initiates cellular
response
Reception
Ligand binds to
the ligand-gated
ion channel,
causing the gate
in the receptor
protein to open
Reception
Intracellular
receptors:
hormones diffuse
through the
membrane and
bind to a receptor
in the cytoplasm.
Once the receptor
is activated, it
usually stimulates
transcription or a
particular gene.
Transduction
Types of transduction pathways:
1. Phosphorilation/dephosphorilation
2. Second messengers
Transduction:
Phosphorilation/deophosphorilation
-Protein kinase: a protein that transfers phosphates from ATP to other
proteins in order to activate them
-Protein phosphatase: enzymes that remove phosphates from proteins
to deactivate them
-Phosphorylation cascade: a series of different molecules are
phosphorylated in turn to bring about a cellular response
Transduction:
Phosphorilation/deophosphorilation
Transduction: Second messengers
-Second messengers are small, non-protein, water soluble molecules
that are activated by reception, diffuse throughout the cell, and
activate another protein to cause cellular response
-Ex. Ca2+, cAMP
Transduction: Second messengers
Response
• Responses usually involve:
1. Turning genes on/off in order to produce or stop producing a
specific protein
2. Altering the activity of a protein that’s already been produced
Cell Signaling Overview
• Types of Cell Signaling
1. Local (paracrine, synaptic)
2. Long distance (endocrine)
• 3 States of cell signaling:
1. Reception
Receptors in Plasma Membrane
GPCR
Ligand-gated ion channel
Intracellular receptors
2. Transduction
Phosphorylation/dephosphorylation
Second messengers
3. Response
Turning genes on/off
Affecting a protein’s activity
Unit Test: Chapters 4 & 5
• Ch 4: Cell Structure
I. Microscopy
II. Prokaryotes vs. eukaryotes
III. Why are cells small?
IV. Eukaryotic cell structure
• Ch 5: Cellular transport
I. Membrane structure and properties
II. Diffusion and osmosis
III. Passive and active transport
IV. Bulk Transport/Cytosis
V. Cell Signaling