Biology 107
Cellular Communication
October 3, 2005
Cellular Communication
Student Objectives: As a result of this lecture and the assigned
reading, you should understand the following:
1.
A cell communicates and interacts with other cells (cell-cell
interactions) and with its extracellular matrix (ECM) (cell-matrix
interactions)
2.
Extracellular communication factors are of two general types: 1)
those that get through the lipid bilayer on their own (e.g., steroid
hormones) or 2) those that act on the outside of the membrane
(e.g., peptide hormones) and require a receptor and transduction
of the signal across the membrane to produce an intracellular
response.
3.
Extracellular communication factors influence such cellular
functions as cell division, metabolism, and gene expression.
Cellular Communication
4.
Cell-cell interactions are achieved by direct cell-cell contact, or by
indirect associations among cells separated by greater or lesser
distances. In addition to communication, direct cell-cell
interactions may be adhesive interactions through cell adhesion
molecules (CAMs), cadherins, or adhering-types of intercellular
junctions.
a. Direct cell-cell communication may occur through
transmembrane molecular signaling or through intercellular
connections - gap (communicating) intercellular junctions
(animals) or plasmodesmata (plants).
b. Indirect interactions are mediated by soluble factors that diffuse
over greater or lesser distances and interact with specific cell
membrane-associated receptor molecules.
Cellular Communication
5.
Signal transduction may lead to receptor changes that directly
affect intracellular events (e.g., altered permeability of an ion
channel) or may indirectly affect intracellular events through
second messenger systems (e.g., cyclic AMP and
diacylglycerol/inositol triphosphate messengers).
6.
Second messengers are small molecules that diffuse rapidly and
amplify the cellular response by acting to directly or indirectly
activate protein kinases, enzymes that attach phosphate groups
from ATP to specific target proteins.
7.
Protein phosphorylation/dephosphorylation is a common mode of
rapid, reversible regulation of protein function. The protein
kinases transfer phosphate groups to proteins, while specific
protein phosphatases remove phosphate groups.
Cells May Interact and Attach to
Their Non-cellular Extracellular
Matrix (ECM)
Cells May
Interact Directly
with Other Cells
Through
Intercellular
Junctions or
Through Cell
Surface
Molecules
Cadherins are Examples of
Adhesive Cell Surface Molecules
that Link Adjacent Cells Together
Attachment
Direct Cell-cell Interactions May
Involve Distinct Junctions
Tight Junctions Connect Adjacent
Cells to Inhibit Movement of
Material Between Cells
Some Intercellular Junctions Have
Direct Cell-Cell Communication as
Their Primary Function
Plasmodesmata are Direct
Cytoplasmic Connections Between
Adjacent Plant Cells
Gap Junctions are Membrane
Channels That Allow Direct
Communication Between Animal Cells
Cell May Interact Indirectly with
Other Cells Through Secreted
Signal That Diffuse to the Target
Mating-type
Signaling in Yeast
Three Major Components of
Signaling are Reception,
Transduction, and the Response
Signals Received on the Outside of
the Cell May Influence Intracellular
Events such as Gene Transcription
Receptors Provide Specificity to
Signaling
Receptor Type Determines the
Intracellular Response to Ligand
Binding
One Consequence of Signal
Transduction is Amplification of the
Response
Second
Messenger
Systems
Amplify the
Initial Signal
and Usually
Work Through
a Protein
Kinase
A Common Second Messenger is
cAMP
cAMP is a nucleotide
cAMP activates a protein kinase
DAG and IP3 are Common Second
Messengers
Both cAMP and
DAG/IP3
Pathways Work
Through GProtein
Intermediates
Interactions of
Different
Transduction
Pathways Lead
to Diversity of
Responses