General Features of Cell Communication

• Cell communication involves cells detecting and responding to signals in the extracellular environment.

• Signals coordinate activities in multicellular organisms.

• Signals lead to responses inside the cell by changing the conformation of receptors.

• Apoptosis is a process where signals intentionally cause a cell to die.

Why Cells Need Signals

• Cells need signals to respond to a changing environment for survival.

  • Example: Glucose signals yeast cells to increase glucose transporters and enzymes for efficient glucose uptake.

• Cells need signals to communicate with each other.

  • Example: Phototropism in plants involves multiple cells changing shape in a coordinated manner using the signaling molecule auxin.

Cellular Receptors and Their Activation

• Ligands are signaling molecules that bind noncovalently to receptors with high specificity.

• Ligand binding leads to a conformational change in the receptor, transmitting the signal across the membrane.

• Three kinds of cellular receptors are enzyme-linked receptors, G-protein coupled receptors (GPCR), and ligand-gated ion channels.

Intracellular Receptors

• Some receptors, like estrogen receptors, are inside the cell.

• Estrogen hormone passes through the cell membrane, binds to the estrogen receptor in the nucleus, and regulates gene transcription.

• Signal transduction pathways may involve a cascade of intracellular kinases or generation of intracellular signals called second messengers

Receptor Tyrosine Kinases

• Enzyme-linked receptors found in animals that recognize various signaling molecules.

• Example: Epidermal Growth Factor (EGF) stimulates cell growth and division in epidermal cells.

G-protein-coupled Receptors

• Signals binding to cell surfaces are the "first messenger."

• Signal transduction pathways lead to the production of second messengers like cAMP and diacylglycerol (DAG).

Second Messengers and Cellular Response

• cAMP provides signal amplification and speed in cellular responses.

• Examples of second messengers include cAMP, DAG