Chapter 11 Cell Communication
Outline
Overview of Cell
Signaling
Types of
receptors
Signal
Transduction
Cellular
Responses to Signals
Figure 11.2 Communication between
mating yeast.
The mating
signal from one yeast cell is results in a specific cellular
response
through a series of steps called a signal transduction pathway.
Signal
transduction is very ancient and is found in prokaryotes, and single and
multicellular eukaryotes.
When
nutrients become scare, individual Myxobacteria signal each other and aggregate
into a spore forming structure.
Types of Cell Signaling
Direct Contact Between
Cells
Local signaling
Paracrine
Signaling
Synaptic
Signaling
Long Distance Signaling
Endocrine
Signaling
Figure 11.3 Communication by
direct contact between cells
Paracrine
Signaling
transmitting cell secretes local regulators that influence
cells in the immediate vicinity.
Fig.11.4a
Synaptic
Signaling
Neurotransmitters
cross chemical synapse between two neurons. Fig 11.4b
Endocrine
Signaling
longer lived, travels through circulatory system.
hormones
The three
stages of cell signaling:
Reception
Transduction
Response
Fig. 11.5
Reception
Detection
of the signal by the target cell
A ligand (signal molecule) binds to a receptor protein
Transduction
The
conformation of the receptor is changed and a signal is relayed via a signal
transduction pathway to the appropriate part of the cell.
Response
A specific cellular response is
triggered.
Includes all possible cellular
activities, for example
genes are turned on/off
cytoskeleton changes shape
Name the steps in signal transduction.
Types of
Receptors
Intracellular
Receptors
Receptors in the
plasma membrane
G-protein-linked receptors
Tyrosine Kinase receptors
Ion channel receptors
Intracellular
Receptors
Located in the
cytoplasm
Recognize
lipid-soluble or very small ligands that can readily cross the plasma membrane
Fig. 11.6
Intracellular
Receptors Can Regulate Genes
Nuclear receptor superfamily
Ligands
Cortisol
Estrogen
Testosterone
Vitamin D
Vitamin A
Transcription factors that regulate genes in
target cells
G-protein-linked
receptors Fig.
11.7
A
membrane protein that interacts with a G protein and another protein,
usually an enzyme.
Widely
used yeast mating factors, epinephrine, many other hormones and
neurotransmitters.
The G protein
functions as a switch that is either on or off.
When GTP is bound, the G protein is active.
When GDP is bound, the G protein is inactive.
Tyrosine Kinase Receptors Fig. 11.7
Growth factors
usually interact with tyrosine kinase receptors.
The cytoplasmic
side of the receptor has tyrosine kinase activity.
Have an
extracellular binding site, an helix that spans the
membrane and an intracellular tail containing a number of tyrosines.
Tyrosine Kinase Receptors Fig. 11.7
Ligand
Gated Ion Channels Fig.
11.7
Protein pores in
the plasma membrane that open and close in response to chemical signaling.
Allows
the flow of a specific kind of ion across the membrane when a specific signal
molecule binds to the extracellular side of the protein.
Protein Kinase Cascades
Amplify the signal
Signal from enzyme linked or G-protein linked receptors is sent to the cytoplasm or the nucleus by a
series of protein kinase reactions.
Amplification occurs at each step.
Figure 11.8 A
phosphorylation cascade
Second
Messengers
Small
molecules that are involved in relaying the signal.
The extracellular
signal is the first messenger
Second messengers
readily spread through the cell.
Examples: cyclic
AMP (cAMP), Ca2+, diacylglycerol,
inositol trisphosphate.
Figure 11.9 Cyclic AMP
Figure 11.10 cAMP
as a second messenger
Figure 11.11 The maintenance
of calcium ion concentrations in an animal cell
Cellular
responses to signals
In response to a
signal, a cell may regulate a variety of activities.
Opening or closing an ion channel
A change in metabolism
A change in gene expression
A change in the conformation of the
cytoskeleton.
Figure
11.13 Cytoplasmic response to a signal: the stimulation of glycogen breakdown
by epinephrine
Figure 11.14 Nuclear
response to a signal: the activation of a specific gene by a growth factor
Elaborate
pathways amplify and specify the cells response to signals.
The signal is
greatly amplified at every step in the signal transduction pathway.
Cell signaling is
highly specific.
Ligand/receptor binding, interactions with G-proteins and
other steps are very specific.
Components of the
pathway have very specific 3-D shapes.
Different cells
have different sets of cell signaling receptors and pathways and will respond
differently.
Figure
11.15 The specificity of cell signaling
The End.
