Cell Signaling and Communication

Cell-Cell Communication

• Cells communicate with each other through various signaling molecules, including neurotransmitters and hormones.
• Hormones are secreted by plant and animal cells into bodily fluids and act on distant target cells.
• Hormones are usually small molecules and can be peptides, steroids, or even gases.

Signal Reception

• Signaling molecules bind to receptor molecules on the target cell, changing the receptor's shape.
• Receptors can be located inside the cell (for lipid-soluble molecules) or on the cell surface (for lipid-insoluble molecules).

Signal Receptors

• The number of receptors in a cell can decline with prolonged exposure to high levels of a signaling molecule.
• The ability of a receptor to bind tightly to a signaling molecule can also decline, affecting cell sensitivity.
• Receptors can be blocked by drugs, such as beta-blockers which bind to adrenaline receptors.

Processing Lipid-Soluble Signaling Molecules

• Lipid-soluble signaling molecules can diffuse across the plasma membrane and enter the cytosol of their target cells.
• These molecules bind to receptors located inside the cell.

Processing Lipid-Insoluble Signaling Molecules

• Lipid-insoluble signaling molecules bind to receptors on the cell surface.

Intracellular Signal Amplification and Diversification

• The signal transmitted by a hormone can be amplified as it changes form within the cell.
• This enables hormones to affect multiple molecules in the cell.
• Amplification can involve various mechanisms, leading to the generation of secondary signals that involve many ions or molecules.

Signal Transduction and Amplification Systems

• G-protein-coupled receptors produce intracellular “second messengers,” which amplify the signal.
• Enzyme-linked receptors amplify the signal by activating a series of proteins inside the cell through the addition of phosphate groups.

G-Protein-Coupled Receptors

• These receptors are associated with membrane-anchored proteins called G proteins.
• G proteins are activated when they bind GTP and inactivated when GDP replaces GTP.
• G proteins regulate the activity of other proteins involved in signal transduction.

Second Messengers

• They can initiate a variety of events in the same cell or in different cell types receiving the same signaling molecule.
• Multiple second messengers may be involved in triggering a cell’s response to the same extracellular signaling molecule.

Explore the intricate processes of cell communication, focusing on how signaling molecules such as hormones and neurotransmitters interact with target cells. Understand the role of signal receptors, their adaptation to signaling molecules, and the effects of external compounds like drugs on receptor activity.