Download BIO508- Topic 8 Lecture Notes File

SoS, Dept. of Biology, Lautoka Campus
BIO508 Cell
Slide Design: Copyright © McGraw-Hill Global Education Holdings, LLC.
Biology
Lecturer: Dr.Ramesh Subramani
Topic 8: Cell Communication
1
How does cell signaling trigger the desperate
flight of this gazelle?
Cellular Messaging
• Cell-to-cell communication is essential for both
multicellular and unicellular organisms
• Biologists have discovered some universal
mechanisms of cellular regulation
• Cells most often communicate with each other
via chemical signals
• For example, the fight-or-flight response is
triggered by a signaling molecule called
epinephrine
External signals are converted to
responses within the cell
• Microbes provide a glimpse of the role of cell
signaling in the evolution of life
Evolution of Cell Signaling
• The yeast, Saccharomyces cerevisiae, has two
mating types, a and 
• Cells of different mating types locate each other
via secreted factors specific to each type
• A signal transduction pathway is a series of
steps by which a signal on a cell’s surface is
converted into a specific cellular response
• Signal transduction pathways convert signals on
a cell’s surface into cellular responses
 factor
Receptor
1 Exchange
of mating
factors
Communication
between mating
yeast cells

a
a factor
Yeast cell,
Yeast cell,
mating type a
mating type 
2 Mating

a
3 New a/ cell
a/
Local and Long-Distance Signaling
• Cells in a multicellular organism communicate by
chemical messengers
• Animal and plant cells have cell junctions that
directly connect the cytoplasm of adjacent cells
• In local signaling, animal cells may communicate
by direct contact, or cell-cell recognition
Plasma membranes
Gap junctions
between animal cells
Plasmodesmata
between plant cells
(a) Cell junctions
(b) Cell-cell recognition
Communication by direct
contact between cells
• In many other cases, animal cells communicate
using local regulators, messenger molecules that
travel only short distances
• In long-distance signaling, plants and animals use
chemicals called hormones
• The ability of a cell to respond to a signal depends
on whether or not it has a receptor specific to that
signal
Local and long-distance cell signaling by
secreted molecules in animals
Local signaling
Long-distance signaling
Target cell
Secreting
cell
Local regulator
diffuses through
extracellular fluid.
(a) Paracrine signaling
Electrical signal
along nerve cell
triggers release of
neurotransmitter.
Endocrine cell
Neurotransmitter
diffuses across
synapse.
Secretory
vesicle
Target cell
is stimulated.
Blood
vessel
Hormone travels
in bloodstream.
Target cell
specifically
binds
hormone.
(b) Synaptic signaling
Paracrine signalling: A secreting cell acts on nearby target cells by
discharging molecules of a local regulator (GF) into the extracellular
fluid.
Synaptic signalling: A nerve cells release neurotransmitter
molecules into a synapse, stimulating the target cell.
(c) Endocrine (hormonal) signaling
The Three Stages of Cell Signaling:
• Earl W. Sutherland discovered how the hormone
epinephrine acts on cells
• Sutherland suggested that cells receiving signals
went through three processes
– Reception
– Transduction
– Response
Cell signaling
EXTRACELLULAR
FLUID
1 Reception
Receptor
Signaling
molecule
CYTOPLASM
Plasma membrane
Cell signaling
EXTRACELLULAR
FLUID
1 Reception
CYTOPLASM
Plasma membrane
2 Transduction
Receptor
Relay molecules in a signal transduction
pathway
Signaling
molecule
Cell signaling
EXTRACELLULAR
FLUID
1 Reception
CYTOPLASM
Plasma membrane
2 Transduction
3 Response
Receptor
Activation
of cellular
response
Relay molecules in a signal transduction
pathway
Signaling
molecule
Reception: A signaling molecule binds
to a receptor protein, causing it to
change shape
• The binding between a signal molecule (ligand)
and receptor is highly specific
• A shape change in a receptor is often the initial
transduction of the signal
• Most signal receptors are plasma membrane
proteins
Receptors in the Plasma Membrane
• Most water-soluble signal molecules bind to
specific sites on receptor proteins that span the
plasma membrane
• There are three main types of membrane
receptors
– G protein-coupled receptors
– Receptor tyrosine kinases
– Ion channel receptors
G protein-coupled receptors
• G protein-coupled receptors (GPCRs) are the
largest family of cell-surface receptors
• A GPCR is a plasma membrane receptor that
works with the help of a G protein
• The G protein acts as an on/off switch: If GDP is
bound to the G protein, the G protein is inactive
Cell-Surface Transmembrane Receptors
G protein-coupled
receptor
Plasma
membrane
Activated
receptor
1
Inactive
enzyme
GTP
GDP
GDP
CYTOPLASM
Signaling
molecule
Enzyme
G protein
(inactive)
2
GDP
GTP
Activated
enzyme
GTP
GDP
Pi
3
Cellular response
4
Receptor tyrosine kinases
• Receptor tyrosine kinases (RTKs) are
membrane receptors that attach phosphates to
tyrosines
• A receptor tyrosine kinase can trigger multiple
signal transduction pathways at once
• Abnormal functioning of RTKs is associated with
many types of cancers
Signaling
molecule (ligand)
Ligand-binding site
 helix in the
membrane
Signaling
molecule
Tyrosines
CYTOPLASM
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Receptor tyrosine
kinase proteins
(inactive monomers)
1
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Dimer
2
Activated relay
proteins
3
Tyr
Tyr
P Tyr
Tyr P
P Tyr
Tyr P
Tyr
Tyr
P Tyr
Tyr P
P Tyr
Tyr P
Tyr
Tyr
P Tyr
Tyr P
P Tyr
Tyr P
6
ATP
Activated tyrosine
kinase regions
(unphosphorylated
dimer)
6 ADP
Fully activated
receptor tyrosine
kinase
(phosphorylated
dimer)
4
Inactive
relay proteins
Cellular
response 1
Cellular
response 2
Ion channel receptors
• A ligand-gated ion channel receptor acts as a
gate when the receptor changes shape
• When a signal molecule binds as a ligand to the
receptor, the gate allows specific ions, such as
Na+ or Ca2+, through a channel in the receptor
Exploring: Cell-Surface Transmembrane
Receptors
1
Signaling
molecule
(ligand)
3
2
Gate
closed
Ions
Plasma
Ligand-gated
membrane
ion channel receptor
Gate closed
Gate
open
Cellular
response
Transduction: Cascades of molecular
interactions relay signals from receptors to
target molecules in the cell
• Signal transduction usually involves multiple steps
• Multistep pathways can amplify a signal: A few
molecules can produce a large cellular response
• Multistep pathways provide more opportunities for
coordination and regulation of the cellular
response
Signaling molecule
Receptor
Activated relay
molecule
Inactive
protein kinase
1
Active
protein
kinase
1
Inactive
protein kinase
2
ATP
ADP
P
Active
protein
kinase
2
PP
Pi
Inactive
protein kinase
3
ATP
ADP
Pi
Active
protein
kinase
3
PP
Inactive
protein
P
ATP
P
ADP
PP
Pi
Active
protein
Cellular
response
Response: Cell signaling leads to
regulation of transcription or cytoplasmic
activities
• The cell’s response to an extracellular signal is
sometimes called the “output response”
Nuclear and Cytoplasmic Responses
• Ultimately, a signal transduction pathway leads to
regulation of one or more cellular activities
• The response may occur in the cytoplasm or in the
nucleus
• Many signaling pathways regulate the synthesis of
enzymes or other proteins, usually by turning
genes on or off in the nucleus
• The final activated molecule in the signaling
pathway may function as a transcription factor
Growth factor
Reception
Receptor
Phosphorylation
cascade
Transduction
CYTOPLASM
Inactive
transcription
factor
Active
transcription
factor
P
Response
DNA
Gene
NUCLEUS
mRNA
• Other pathways regulate the activity of enzymes
rather than their synthesis
• Signaling pathways can also affect the
overall behavior of a cell, for example,
changes in cell shape
Apoptosis integrates multiple cellsignaling pathways
• Apoptosis is programmed or controlled cell
suicide
• Components of the cell are chopped up and
packaged into vesicles that are digested by
scavenger cells
• Apoptosis prevents enzymes from leaking out of a
dying cell and damaging neighboring cells
Apoptosis of a human white blood cell
2 m
• Apoptosis evolved early in animal evolution and is
essential for the development and maintenance of
all animals
• Apoptosis may be involved in some diseases (for
example, Parkinson’s and Alzheimer’s);
interference with apoptosis may contribute to
some cancers
Effect of apoptosis during paw
development in the mouse.
Interdigital tissue
Cells undergoing
apoptosis
Space between
1 mm
digits
Acknowledgements…
 The teaching material used in this lecture is taken from: JB Reece, LA
Urry, ML Cain, SA Wasserman, PV Minorsky and RB Jackson. 2011.
Campbell Biology (9th Edition), Publisher Pearson is gratefully
acknowledged.
 Some information presented in this power point lecture presentation is
collected from various sources including Google, Wikipedia, research
articles and some book chapters from various biology books. Material and
figures used in this presentation are gratefully acknowledged. This
material is collected and presented only for teaching purpose.
Any Questions??
Dr.Ramesh Subramani, Assistant Professor in Biology