Download Cell Signaling - Scott County Schools

Cell to Cell Communication
Cell-to-cell communication
•Communication is essential for multicellular organisms
•Cells must coordinate activities in a way that
enables them to develop, survive and
reproduce.
Evolution of Cell Communication/ Signaling
• 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
• Pathway similarities suggest that ancestral signaling
molecules evolved in prokaryotes and were modified later in
eukaryotes
• Cell signaling evolved well before first multicellular organisms
(evidence for a common ancestor)
Proteins in the membrane!
• Proteins are embedded in the
phospholipid bilayer– these
play a major role in cell
signaling
• Integral proteinstransmembrane proteins which
span the bilayer.
• Peripheral proteins- not
embedded in the bilayer– on
the surface.
Animal Cells intercellular junctions
• Tight junctions- membranes of neighboring
cells tightly pressed against each other
bound by proteins to form continuous cells
around cells (skin cells)
• Desmosomes- cells are fastened together
into strong sheets (muscle cells)
• Gap junctions- membrane proteins that
surrounds a port through which ions, sugars,
amino acids and other small molecules may
pass.
Plasma membranes
Gap junctions
between animal cells
(a) Cell junctions
(b) Cell-cell recognition
Plasmodesmata
between plant cells
Types of Communication in Animal Cells
1. If there are gap junctions, cytoplasm of adjacent cells connects. Signaling
substances are dissolved in the cytoplasm and pass freely between cells
2. Animal cells may communicate by cell-to-cell recognition. Ex: immune
response and development
3. Messenger molecules secreted by signaling cell can travel short distances.
These are called local regulators– they influence cells in the vicinity.
(paracrine signaling – growth of cells/ synaptic signaling– nervous system)
4. Hormones- long distance signaling ex: endocrine system (travels through
circulatory system. Large variation of molecules)
Long-distance signaling
Local signaling
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Target cell
Secreting cell
Local regulator
diffuses through
extracellular fluid
a) Panacrine signaling
Neurotransmitter
diffuses across
synapse
Target cell
is stimulated
b) Synaptic signaling
Cell Signaling– three Stages
1. Reception- Detection of signaling molecule
2. Transduction (changing of signal)- binding of signaling
molecule changes receptor protein in some way
1. Transduction converts signal to a form that can bring about
a cellular response.
3. Response- Triggers response- can be many different things
such as catalysis by an enzymes, activation of genes, etc.
Transduced= changed
• Signal transduction pathways- signal of a cells’ surface is converted to
a specific cellular response in a series of steps.
1. Reception
2. Transduction
(changing signal)
Activation
of Cellular
Response
Receptor
Relay molecules in a signal transduction pathway
Signaling
Molecule
3. Response
Step 1. Reception(Signal transduction
pathways)
• Signaling begins with the recognition of a chemical
messenger, a ligand, by a receptor protein.
• Ligand- a molecule that binds to another molecule
(signal! Molecule)
• Receptor protein usually undergoes a change in shape
when a ligand binds (similar to allosteric regulation in
enzymes) which initiates transduction of the signal.
Receptor Protein Example
• There are many types of receptor
proteins!
• Different receptors recognize
different chemical messengers,
which can be peptides, small
chemicals or proteins, in a specific
one-to-one relationship.
• Example of on type of receptor
protein: Receptor tyrosine kinases.
• A kinase is an enzyme that catalyzes
phosphate (Pi) group transfer.
• Many pathways may be triggered by
one ligand!!
Step 2: Transduction
• Signal transduction is process by which a signal is converted to a
cellular response.
• Transduction is usually a multi-step pathway (like falling
dominoes!)--- can be called signaling cascades.
• Benefit of multiple steps:
1. Possible to greatly amplify signal (many responses for one
signal)
2. More opportunities for regulation
•Molecules that relay a signal from a receptor
to responses are often PROTEINS!
•Protein interaction is a major theme in
regulation at the cellular level (thanks
proteins!)
•Remember! The original signaling molecule
does not enter the cell… is all a message of
proteins.
In transduction, proteins change shape
• Proteins are activated by adding energy (from ATP!!)
• If we give a protein energy from ATP, it get a phosphate
group and is phosphorylated. (What process gives us ATP??)
• Kinases are enzymes that transfer a Pi. Protein kinases
transfer Pi to a protein.
• Many of the relay molecules (dominoes) are protein kinases
in transduction and they often act on other protein kinases.
• Falling dominoes= protein kinase cascade.
Protein Kinase Cascade= falling dominoessignal transduction
Protein phosphatases remove Pi from
proteins
• Protein phosphatases preform dephosphorylation on proteins.
• When they dephosphorylate, they inactivate protein kinases and
turn of the signal transduction pathway when the initial signal is
no longer there.
• Phosphorylation/dephosphorylation system act as a molecular
switch in the cell, turning cell activities on or off.
Secondary messengers are often important in
the cascade (dominoes)
• Not all components of signal transduction pathways are
proteins (thanks proteins)
• Many pathways involve small, water-soluble molecules
called secondary messengers
• Since they are small and water-soluble, they diffuse
through the cell easily (but you guys already knew that).
Step 3: Response
• Signal transduction pathways lead to one or more cellular
activities– occurs in the nucleus or the cytoplasm.
• Many regulate protein synthesis (thanks proteins!) by
turning on or off specific gene
• Many regulate the activity of proteins (thanks proteins!)