Download Lecture 19: Cell communication

Biological
Hierarchy:
Cell to Cell Communication
• Involves (and you should review):
• Structure of plasma membranes
• Diffusion vs. active transport
• Hydrophobic vs. hydrophilic compounds
• Proteins
• Surface vs. intermembrane proteins
• Enzyme activity
Figure 8.7 The structure of a transmembrane protein
Figure 8.9 Some functions of membrane proteins
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Receptor protein
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Receptor protein
Cells can communicate by direct contact between cells
Cells can communicate by sending chemical signals to
other cells:
Mating in yeast
cells depends on
cell to cell
communication
Chemical signals can be sent to cells at various distances
from each other
Once a chemical signal reaches its
target cell:
• Signal molecule binds to a receptor protein on
the target cell (it is a ligand)
• The receptor molecule changes shape
• The shape change causes a series of reactions
(transduction) to take place in the cytoplasm
of the cell
• This series of reactions leads to a response of
the cell to the chemical signal
• This process is called a signal-transduction
pathway
Figure 11.5 Overview of cell signaling (Layer 1)
Figure 11.5 Overview of cell signaling (Layer 2)
Figure 11.5 Overview of cell signaling (Layer 3)
Common Types of Receptors
• G-protein-linked receptors
• Tyrosine-kinase receptors
• Ligand-gated ion-channel receptor
• Intracellular receptors
G-protein-linked receptors
When G-proteinlinked receptors
receive a signal, they
will activate a “G
protein” inside the
cell
The G-protein starts
the transduction
pathway leading to
the cell response
Tyrosine-kinase receptors act as an enzyme, using ATP to start
several transduction pathways simultaneously
Ligand-gated ion-channel
receptors open or close in
response to a chemical signal,
allowing ions to DIFFUSE in or
out of the cell based on relative
concentrations
Lipid-soluble chemical
signals, such as steroid
hormones, can pass
through the plasma
membrane, and bind to an
intracellular receptor
Inside the cell, the activated
receptor may turn on or off
certain genes
(a transcription factor)
Once the signal has been received by the receptor, this triggers the
transduction pathway, that eventually leads to the cell’s response
Fig. 11.11: A phosphorylation cascade
Some signaltransduction
pathways involve
the use of small,
non-protein
molecules or ions.
These are called
second
messengers
Second messengers
often bind to and
activate other
enzymes in the
pathway
Cyclic AMP (cAMP) is a common second messenger
Calcium ions are also used as second messengers
The concentration of
calcium is kept low
in the cytoplasm of
animal cells by
actively pumping
them into the
mitochondria and
the ER and out of
the cell
Calcium is used by both G-protein and tyrosine-kinase pathways
as a second messenger
Inositol triphosphate (IP3) opens a channel that releases Ca2+
into the cytoplasm
Calcium activates calmodulin which turns on or off other
proteins
An example of an entire pathway
In times of physical stress,
the adrenal glands release
the hormone epinephrine
Fuel reserves are mobilized
by the breakdown of
glycogen to individual
glucose molecules
The response of a cell to
signal can be varied:
1. Turning on certain
enzymes
2. Turning on/off genes and
protein production
3. Muscle contraction
4. Cell division
etc…
The response of a cell to a signal depends on what type of cell
it is and what other types of proteins are present in the cell