Transcript Cell Communication

Cell Communication
http://www.dnalc.org/ddnalc/c
ell_signals/index.html
Cell Signaling
 Signal-transduction pathway- how a signal on
a cell’s surface is changed into a cellular
response.
 Cells secrete local regulators which is a
substance that influences cells that are
near. Ex. Growth factors, compounds that
trigger cells to grow and multiply
 A common compound used in animals and
plants are hormones.
Cell Signaling Cont..
 Two types of information available
 1. Direct physical aspects of the
environment
 2. Symbolic information encoded by
other cells
Overview of Cell signaling
http://www.dnatube.com/video/233/TheSignal-Transduction-Pathway
Symbolic information is required
for multicellular organisms
 Bacteria (unicellular organisms) sense their
environment and change their behavior (i.e.
chemotaxis).
 To coordinate the behavior of populations of
cells, cells in multicellular organisms must
exchange data.
 http://www.sysbio.org/resources/tutorials/
2003series/biolecture5.pdf
Vocabulary
 Hormone -circulating, global regulator made
by endocrine glands
http://www.sumanasinc.com/webcontent/anim
ations/content/extracellularsignaling.html
 Growth factor -polypeptide that promotes cell
growth and/or proliferation
 Cytokine -general term for a growth factor,
derived from immunology
 Chemokine -small factor involved in cell
attraction and migration
Examples of Cell Signaling
http://www.dnatube.com/video/2349/Syna
ptic-Signaling
http://www.allthingsscience.com/video/665
/The-Endocrine-System-How-it-Works
Communication by Direct
Contact Between Cells
Interaction of Cell-Surface
Molecules
Stages of Cell Signal
 1. Reception- a chemical signal is detected
when it binds to a cellular protein, usually at
the cells surface.
 A cell needs to communicate with its
environment so that it can make appropriate
responses. The external signal may enter a cell
via four major pathways:
 1.Hydrophobic molecules.
http://highered.mcgrawhill.com/sites/0072507470/student_view0/chapt
er17/animation__intracellular_receptor_model.h
tml
 2.Ion channels.
 3.G-protein-coupled receptors.
Hydrophobic
molecules.
Ion channel
G-protein-coupled
receptors
Enzymes
Stages of Cell Signal Cont..
 2. Transduction-The binding of the signal
molecule changes the receptor protein in
some way, in order to initiate the process of
transduction. This stage converts the signal
to a form that can bring about a specific
cellular response. Transduction often occurs
in a single step but more often requires a
sequence of changes in a series of different
molecules- a signal-transduction pathway.
The molecules in the pathway are often
called relay molecules.
Transduction
Stages of Cell Signal Cont..
 3. Response- the transduction triggers a
response.
 http://cgmp.blauplanet.com/transd.html
Reception
Binding of epinephrine to G-protein-linked receptor (1 molecule)
Transduction
Transduction
Inactive G protein
Active G protein (102 molecules)
Inactive adenylyl
cyclase
Active adenylyl cyclase (102)
ATP
Cyclic AMP (104)
Active protein kinase
A (105)
Inactive protein kinase A
Inactive phosphorylase kinase
Inactive glycogen
phosphorylase
Active
phosphorylation
Active glycogen
phosphorylase (106))
Response
Glycogen Glucose-1-phosphate
(108 molecules)
Ligand
 A signal molecule binds to a receptor protein, causing
the protein to change shape.
 A ligand is a small molecule that binds to a larger
one.
 Ligand binding generally causes a receptor protein to
undergo a change in shape. For many receptors this
change directly activates the receptor so that it can
interact with another cellular model.
Plasma-Membrane proteins
 1. G-protein-linked receptors- is a plasma-membrane
receptor that works with the help of a protein called
G protein linked receptors, including epinephrine and
other hormones and neurotransmitters. All G protein
receptor molecules are structurally similar. The G
protein functions as a switch that is on or off
depending on which guanine nucleotides is attached,
GDP or GT When GDP is bound it is inactive, when
GTP is bound it is active. (GTP or guanosine
triphosphate is similar to ATP).
 When the appropriate chemical signal binds as a
ligand to the outside of a G-protein-linked receptor,
the receptor is turned on changing the conformation
in a way that it, in turn can activate a G protein.
G Protein Cont…
 The receptor binds a specific, inactive G
protein and causes a GTP to displace the
GDP. The activated G protein then binds to
another protein, usually an enzyme and alters
its activity.
 This is temporary for the G protein also
functions as a GTPase enzyme. The GTPase
function of the G protein allows the pathway
to shut down rapidly when the outside signal
is no longer present.
 http://www.celanphy.science.ru.nl/Bruce%20
web/Flash%20Movies.htm
Cont..
 G proteins are involved in sensory reception.
Ex: vision (vitamin A) and smell.
 60% of all medications used today are a
result of an influence on a G protein
pathway.
 http://highered.mcgraw-
hill.com/sites/0072507470/student_view0/chapter1
7/animation__membranebound_receptors_that_activate_g_proteins.html
 http://highered.mcgrawhill.com/sites/0072507470/student_view0/chapter1
7/animation__membranebound_receptors__g_proteins__and_ca2__channels.
html
Plasma-Membrane proteins Cont…
 2. Tyrosine-Kinase Receptors- tyrosine kinase
an enzyme, catalyzes the transfer of
phosphate groups from ATP to the amino acid
tyrosine on a substrate protein. The tyrosinekinase receptors are the membrane receptors
that attach phosphates to protein tyrosines.
 http://media.pearsoncmg.com/bc/bc_campbe
ll_biology_7/media/interactivemedia/activitie
s/load.html?11&B
Tyrosine Cont..
 A. The ligand binding causes two receptor
polypeptides to come together, making a
dimer (a protein consisting of 2 polypeptides).
 B. This activates the tyrosine-kinase of both
 C. Which phosphorylates the tyrosines on the
tail of the other
 http://faculty.plattsburgh.edu/donald.slish/t
yrosinekinase/TK1.html
 Abnormal tyrosine-kinase that come together
without ligand can cause cancer.
Plasma-Membrane proteins Cont…
 3. Ion-Channel Receptors
 These are ligand gated ion channels that are
protein pores in the plasma membrane that
open or close in response to a chemical
signal, allowing or blocking the flow or
specific ions such as Na+ or Ca2+.
 These channel proteins bind a signal
molecule as a ligand at a specific site on the
outside of the cell. The shape change
produced in the channel protein immediately
leads to a change in the concentration of a
particular ion in the cell.
 Ex: Synapse between nerve cells
Ion-Channel Receptors
 http://www.
mind.ilstu.ed
u/flash/synap
se_1.swf
 http://www.wiley.
com/legacy/college
/boyer/0470003790
/animations/memb
rane_transport/me
mbrane_transport.h
tm
Intracellular receptors
 Some signal receptors are proteins located in
the cytoplasm or nucleus of target cells. So
in order to reach the receptor a chemical
message must be able to pass through the
target cells membrane.
 Ex: Testosterone, it enters the target cells
binds to the receptor molecules, activating it.
The protein then can bind and turn on genes
in the nucleus that control male sex
characteristics.
Intracellular Animation
 http://highered.mcgraw-
hill.com/olc/dl/120069/bio06.swf
Advantages
 A very small number of extracellular
signal molecules can produce a major
cellular response.
 Multistep pathways provide more
opportunities for coordination and
regulation than simpler systems.
 To Amplify the signal:
 http://highered.mcgrawhill.com/olc/dl/120069/bio08.swf
Protein Phosphorylation
 Phosphorylation is a common mode of cell
regulation.
 Protein kinase is the name for an enzyme
that transfers phosphate groups from ATP to
a protein.
 Most cytoplasmic protein kinases act on
other substrate proteins and phosphorylate
their substrates on either the amino acid
serine or threonine.
 These are common in animals, fungi and
plants.
 http://media.pearsoncmg.com/bc/bc_campbell_bio
logy_7/media/interactivemedia/activities/load.htm
l?11&C
Phosphorylation Cascade
Second Messengers
 Many signaling pathways involve small,
nonprotein, water-soluble molecules or ions
call second messengers.
 The extracellular signal molecule that binds
to the membrane receptor is the first
messenger.The second messenger is small and
water-soluble so can pass through the
membrane by diffusion.That relay the
message from the inside of the membrane
throughout the cytoplasm.
 Ex: cAMP (cyclic AMP) that carries the signal
initiated by epinephrine from the plasma
membrane of a liver or muscle cell into the
cell’s interior
cAMP
 cAMP (cyclic AMP (adenine monophosphate) ).
 An enzyme built into the cell membrane,
adenylyl cyclase, converts ATP to cAMP in
response to an extracellular signal, in this
case epinephrine. Adenylyl cyclase only
becomes active only after epinephrine binds
to a specific receptor protein.
 So the first messenger the hormone, causes a
membrane enzyme to make cAMP, which
sends the signal to the cytoplasm.Then
another enzyme converts the cAMP into an
inactive form. In order for this to happen
again you need more epinephrine.
cAMP
 http://highered.mc
grawhill.com/olc/dl/120
069/bio07.swf
Disease
 Some diseases, like cholera produce an
enzyme that changes a G protein that is
involved in regulating salt and water
secretion. Because the changed protein can
no longer hydrolyze GTP to GDP, it remains
stuck in its active form, continuing to
stimulate cAMP causing intestinal cells to
secrete large amounts of water and salts
into the intestine. Which results in bad
diarrhea and the victim can die if untreated.
Calcium
 Another second messenger is Ca+ in G
pathways and tyrosine-kinase receptor
pathways.
 Ca+ that is released from the ER
triggers cleavage of certain
phospholipids on the cell membrane.
Cellular Responses
 These can result in activities in the cytoplasm
such as a rearrangement of the cytoskeleton.
 Sometimes they regulate the making enzymes
or other proteins by turning off or on specific
genes.
 Cellular responses are very specific. Different
kinds of cells have different collections of
proteins.
 One signal molecule may lead to more than
one response, activate or inhibit another
response.
 http://media.pearsoncmg.com/bc/bc_campbell_biolo
gy_7/media/interactivemedia/activities/load.html?11
&D
Activity
 http://media.pearsoncmg.com/bc/bc_
campbell_biology_7/media/interactive
media/activities/load.html?11&E