Biology 107Biology 107

Cellular CommunicationCellular Communication

October 6, 2003October 6, 2003

Cellular CommunicationCellular CommunicationStudent Objectives:Student Objectives: As a result of this lecture and the assigned As a result of this lecture and the assigned

reading, you should understand the following:reading, you should understand the following:

1.1. A cell communicates and interacts with other cells (cell-cell A cell communicates and interacts with other cells (cell-cell interactions) and with its extracellular matrix (interactions) and with its extracellular matrix (ECMECM) (cell-matrix ) (cell-matrix interactions)interactions)

2.2. Extracellular communication factors are of two general types: 1) Extracellular communication factors are of two general types: 1) those that get through the lipid bilayer on their own (e.g., steroid 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 hormones) or 2) those that act on the outside of the membrane (e.g., peptide hormones) and require a receptor and transduction (e.g., peptide hormones) and require a receptor and transduction of the signal across the membrane to produce an intracellular of the signal across the membrane to produce an intracellular response. response.

3.3. Extracellular communication factors influence such cellular Extracellular communication factors influence such cellular functions as cell division, metabolism, and gene expression.functions as cell division, metabolism, and gene expression.

Cellular CommunicationCellular Communication4.4. Cell-cell interactions are achieved by direct cell-cell contact, or by Cell-cell interactions are achieved by direct cell-cell contact, or by

indirect associations among cells separated by greater or lesser indirect associations among cells separated by greater or lesser distances. In addition to communication, direct cell-cell distances. In addition to communication, direct cell-cell interactions may be adhesive interactions through cell adhesion interactions may be adhesive interactions through cell adhesion molecules (CAMs), cadherins, or adhering-types of intercellular molecules (CAMs), cadherins, or adhering-types of intercellular junctions.junctions.

a.a. Direct cell-cell communication may occur through Direct cell-cell communication may occur through transmembrane molecular signaling or through intercellular transmembrane molecular signaling or through intercellular connections - gap (communicating) intercellular junctions connections - gap (communicating) intercellular junctions (animals) or plasmodesmata (plants).(animals) or plasmodesmata (plants).

b.b. Indirect interactions are mediated by soluble factors that Indirect interactions are mediated by soluble factors that diffuse diffuse over greater or lesser distances and interact with specific over greater or lesser distances and interact with specific cell cell membrane-associated receptor molecules.membrane-associated receptor molecules.

Cellular CommunicationCellular Communication

5.5. Signal transduction may lead to receptor changes that directly Signal transduction may lead to receptor changes that directly affect intracellular events (e.g., altered permeability of an ion affect intracellular events (e.g., altered permeability of an ion channel) or may indirectly affect intracellular events through channel) or may indirectly affect intracellular events through second messenger systemssecond messenger systems (e.g., cyclic AMP and (e.g., cyclic AMP and diacylglycerol/inositol triphosphate messengers). diacylglycerol/inositol triphosphate messengers).

6.6. Second messengers are small molecules that diffuse rapidly and Second messengers are small molecules that diffuse rapidly and amplify the cellular response by acting to directly or indirectly amplify the cellular response by acting to directly or indirectly activate protein activate protein kinaseskinases, enzymes that attach phosphate groups , enzymes that attach phosphate groups from ATP to specific target proteins.from ATP to specific target proteins.

7.7. Protein phosphorylation/dephosphorylation is a common mode of Protein phosphorylation/dephosphorylation is a common mode of rapid, reversible regulation of protein function. The protein rapid, reversible regulation of protein function. The protein kinases transfer phosphate groups to proteins, while specific kinases transfer phosphate groups to proteins, while specific protein phosphatases remove phosphate groups.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

AttachmentAttachment

Mating-type signaling in yeast

Cell May Interact Indirectly with Other Cells Through Secreted Signal That Diffuse to the

Target

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 nucleotidecAMP is a nucleotide

cAMP activates a protein kinasecAMP activates a protein kinase

DAG and IP3 are Common Second Messengers

Both cAMP and DAG/IP3 Pathways Work Through G-Protein Intermediates

Interactions of Different Transduction Pathways Lead to Diversity of Responses