Transcript Cell to Cell Communication

Cell to Cell
Communication
Why do cells need to
communicate?
 Cells must communicate to coordinate their activities!!
 Cells respond to internal signals AND external signals
Unicellular Organism
Communication
 Signals = changes in the environment
 Responses = changes in gene expression
 Ex: Quorum Sensing, Inducible operons, Repressible
Operons
Quorum Sensing
 Ex: Results in Production of Toxins
Lac Operon
 Responding to changes in the environment
Multicellular Signaling
Pathways
 Allows for coordination
of ALL of the cells of
the organisms in
responding to various
stimuli
 Ex: Fight or Flight
Response (Epinephrine)

Signal Transduction is
UNIVERSAL
All organisms have signal
transduction pathways
 MAJOR area of evolution!
 Heavily adapted by natural
selection
What are the various ways that cells
can communicate?
Cell-Cell Contact
(Juxtacrine)
 Plasmodesmata: Channels in the
cell walls of plant-like cells which
allow for direct passage of
materials and signaling molecules
Immune System Cells
 Communication between lymphocytes (white blood
cells)
Paracrine Signaling
 Neurotransmitters
Interferons in Immune
System
Endocrine Signaling –
Long-Distance
 Hormones
 Insulin/Glucagon
Human Growth
Hormone
 Sex
Hormones
–Menstrual
Cycle
 How does
birth
control
work?
Sex Hormones Testosterone
What are the three phases
of cell communication?
 The process must involve three stages.
 Reception, detection
 Transduction, transmission of signal
 Response, cellular response to the signal
7. What is a ligand?
What is a ligand?
 A signaling molecule involved in the reception stage
 polar (protein based, charged, peptide) and nonpolar
(lipid based, steroid)
Receptor Proteins
 Tons of Diversity…but three basic
characteristics:
 Area to interact with ligand (MATCHING
SHAPE!)
 Area that transmits the signal to another protein
 Conformational change in shape following ligand
interaction
Ex: G-Protein-Linked
Receptor
 A ligand binds to G-protein linked receptor
 Conformational change in receptor causes
phosphorylation of a G-protein (activation)
 Activated G-protein phosphorylates the next protein
in the pathway
Ex: Ligand-gated
Ion Channels
 Ligand binds to the channel protein
(receptor)
 Conformational Change causes the
channel to open
 Ions move freely into the cell and
Trigger cellular responses
 Very important in NERVOUS
SYSTEM
Ex: Intracellular Receptors
 Can be found in the cytoplasm or the nucleus
 Bind to nonpolar (hydrophobic, steroid, lipid-based)
ligands
Is this a protein or steroid
ligand?
Is this a protein or steroid
ligand?
Is this a protein or steroid
ligand?
STAGE 2:
TRANSDUCTION
 Transduction converts signal reception into a
cellular response
 Accomplished by activation of proteins through
phosphorylation (kinase enzymes), or a change in
intracellular conditions
Second Messengers
 Internal signaling
molecules, often
activated by multiple
external signals
 Aid in amplification
of signal
 Ex: cyclic AMP
(cAMP) and Ca2+.
Pathway involving cAMP
as a secondary
messenger.
Pathway using Ca2+ as
a secondary
messenger.
The Response
 Cell responses involve changes in gene
expression, and the activation of already
synthesized, inactive proteins
Ex: Epinephrine
One ligand, many responses
Ex: Testosterone: A steroid
Hormone
 Bind to intracellular
receptors
 Enter the nucleus and act
as transcription factors
activate gene expression
of male specific genes
Benefits of Multiple Steps
 They amplify the response to a signal.
 They contribute to the specificity of the
response.
 Allow for multiple points of regulation
Alterations in Signal
Transduction Pathways
disrupt homeostasis
 Diabetes – Type I and Type II
 Parkinston’s Syndrome
 Cancer
 Cholera
Short Answer Question
 The figure above represents a generalized hormone-
signaling pathway. Briefly explain the role of each
numbered step in regulating target gene expression.
(3 points maximum)
•
Step 1 = hormone/ligand binding to
receptor to initiate/trigger/induce signaling OR
signal reception
•
Step 2 = an intracellular cascade that
transduces/amplifies/transfers the signal from
plasma membrane to nucleus (or other cellular
effectors)
•
Step 3 = transcription/expression of target
genes is stimulated/repressed
Many drugs work by
altering signal
transduction pathways
 Antihistamines
 Birth Control