Cell Communication

cell junctions

[both animals and plants have cell junctions that allow muscles to pass readily between adjacent cells without crossing plasma membrane]

Explain the evolution of cell signaling!

Signaling in microbes has much in common with processes in multicellular mechanisms, suggesting an early origin of signaling mechanisms. Bacterial cells can sense the local density of bacterial cells by binding molecules secreted by other cells. In some cases, such signals lead to aggregation of these cells into biofilms.

What are three stages of cell signaling?

1. reception

2. transduction

3. response

What is apoptosis?

Apoptosis is a type of programmed cell death in which cell components are disposed of in an orderly fashion, without damage to neighboring cells.

Facts:

- In local signaling, animal cells may communicate by direct contact or by secreting local regulators, such as growth factors or neurotransmitters.

- The binding between signaling (ligand) and receptor is highly specific.

- Intracellular receptors are cytoplasmic or nuclear proteins.

- The behavior of testosterone is representative of steroid hormones.

- Most water-soluble molecules bind to specific sites on receptor proteins embedded in the cell’s plasma membrane.

Key terms:

Signal transduction pathway = series of steps when a signal on a cell’s surface is converted to a specific cellular response

Local regulators = influence cells in the vicinity

Hormones = chemicals for long-distance signaling

Ligand = a molecule that binds specifically to another molecule, usually a larger one

Cyclic AMP/ cAMP = cyclic adenosine monophosphate, a ring-shaped molecule made from ATP that is common intracellular signaling molecule (second messenger)

Receptor tyrosine kinase proteins = inactive monomers

Protein kinase = an enzyme that transfers phosphate groups from ATP to a protein

Adenylyl cyclase = an enzyme embedded in the plasma membrane; converts ATP to camp in response to extracellular signals

Scaffolding proteins = large relay proteins to which several other relay proteins are simultaneously attached

Apoptosis = a program of controlled cell suicide

Summary:

Signaling in microbes has much in common with processes in multicellular organisms, with processes in multicellular organisms, suggesting an early origin of signaling mechanisms. In local signaling, animal cells may communicate by direct contact or by secreting local regulators, such as growth factors or neurotransmitters. For signaling over long distances, both animals and plants use hormones. Earl Sutherland discovered how the hormone epinephrine acts on cells: the signal is transmitted by successive shape changes in the receptor and relay molecules.

The binding between a ligand and receptor is highly specific. The change of the receptor is often the initial transduction of the signal. A G protein-coupled receptor is a membrane receptor that works with the help of a cytoplasmic G protein. Ligand binding activates the receptor, which then activates a specific G protein, which activates another, propagating the signal along a signal transduction pathway. Another receptor in the plasma membrane is tryosine kinase. Specific signaling molecules cause ligand-gated ion channels in a membrane to open or close, regulating the flow of specific ions. Intracellular receptors are cytoplasmic or nuclear proteins.

Cascades of molecular interactions relay signals from receptors to target molecules in the cell.

Cell signaling leads to regulation of transcription or cytoplasmic activities.

Apoptosis is a type of programmed cell death in which cell components are disposed of in an orderly fashion, without damage to neighboring cells.

Extra:a real example of cell communication

(video!)