Biology Chapter 11: Cell Communication (Key Terms)

Signal Transduction Pathways

Signal Transduction Pathways

A series of steps linking a mechanical, chemical, or electrical stimulus to a specific cellular response.

Quorum Sensing

phenomenon through which bacteria can sense the concentration of signaling molecules secreted by other bacteria, allowing them to monitor their own local cell density

Biofilm

An aggregation of bacterial cells attached to a surface by molecules secreted by the cells.

• The biofilm protects the cells in it, and they often derive nutrition from the surface they are on.

• Biofilms are believed to be involved in up to of all human bacterial infections.

Hormones

One of many types of secreted chemicals that are formed in specialized cells, travel in body fluids, and act on specific target cells in other parts of the organism, changing the target cells’ functioning

Growth Factors

One class of local regulators in animals that consists of compounds that stimulate nearby target cells to grow and divide.

Paracrine Signaling

a form of cell communication in which cells produce signals that affect nearby target cells.

• involves the release of signaling molecules, such as hormones or neurotransmitters, which diffuse through the extracellular space to influence the behavior of adjacent cells.

Synaptic Signaling

a form of cell communication in which neurons communicate with each other at synapses.

• An electrical signal along a nerve cell triggers the secretion of neurotransmitter molecules. These molecules act as chemical signals, diffusing across the synapse—the narrow space between the nerve cell and its target cell—triggering a response in the target cell.

• Drugs to treat depression, anxiety, and post-traumatic stress disorder (PTSD) affect this signaling process.

Endocrine (hormonal) Signaling

a type of cell communication that involves the release of hormones from endocrine cells into the bloodstream to reach target cells throughout the body. The hormones bind to receptors on the target cells, producing a long-lasting response.

Autocrine Signaling

a type of cell communication where a cell secretes a chemical messenger or hormone that binds to receptors on the same cell, causing changes in that cell

Neurotransmitters

chemical messengers (i.e., dopamine, serotonin)

Receptors

proteins on the postsynaptic membrane that bind to neurotransmitters.

Synaptic Cleft

The gap between neurons where signaling occurs.

3 Stages of Cell Signaling

1: Signal reception

2: Signal transduction

3: Cellular Response

(1) Signal Reception

The target cell’s detection of a signal molecule coming from outside the cell.

• a chemical signal is detected when the signal molecule binds to a receptor protein located on the cell’s surface or inside the cell

(2) Signal Transduction

The binding of the signaling molecule changes the receptor protein in some way, initiating the process of transduction.

• This stage converts the signal to a form that can bring about a specific cellular response.

• sometimes occurs in a single step but more often requires a sequence of changes in a series of different molecules—a signal transduction pathway.

(3) Cellular Response

The transduced signal finally triggers a specific cellular response .The cell-signaling process helps ensure that crucial activities like these occur in the right cells, at the right time, and in proper coordination with the activities of other cells of the organism.

• The response may be almost any imaginable cellular activity—such as catalysis by an enzyme, rearrangement of the cytoskeleton, or activation of specific genes in the nucleus.

Ligand

Term used for a molecule that specifically binds to another (often larger) molecule.

• this type of binding generally causes a receptor protein to undergo a change in shape

G-Protein Coupled Receptors (GPCRs)

Cell-surface transmembrane receptors that respond to the binding of a specific G protein.

• these are the largest family of human cell-surface receptors

• GPCR-based signaling systems are extremely widespread and diverse in their functions

Receptor Tyrosine Kinases (RTKs)

A major class of plasma membrane receptors characterized by having enzymatic activity (draft card)

Transcription Factors

specialized proteins that control which genes are turned on—that is, which genes are transcribed into mRNA—in a particular cell at a particular time.

• receptors of cell signals can act as transcription factors, controlling which genes are activated

Phosphorylation Cascade

A series of chemical reactions during cell signaling mediated by kinases, in which each kinase in turn phosphorylates and activates another, ultimately leading to phosphorylation of many proteins.

Protein Kinases

Enzymes that transfer phosphate groups from ATP to protein, thus phosphorylating the protein.

Protein Phosphatases

enzymes that remove phosphate groups from (dephosphorylates) proteins, often functioning to reverse the effect of a protein kinase.

Second Messengers

molecules that relay messages in a cell from a receptor to a target where an action within the cell takes place.

Cyclic AMP (cAMP)

named because of its ring structure; a common chemical signal that has a diversity of roles, including as a second messenger in many eukaryotic cells, and as a regulator of some bacterial operons.

Adenylyl Cyclase

An enzyme that converts ATP to Cyclic AMP in response to an extracellular signal.

Diacylglycerol (DAG)

A second messenger produced by the cleavage of the phospholipid PIP2 in the plasma membrane.

Inositol Trisphosphate (IP₃ )

A second messenger that functions as an intermediate between certain signaling molecules and a subsequent second messenger, Ca²⁺ , by causing a rise in cytoplasmic Ca²⁺ concentration.

Scaffolding Protein

A type of large relay protein to which several other relay proteins are simultaneously attached, increasing the efficiency of signal transduction.

G Protein

a GTP-binding protein that relays signals from a plasma membrane signal receptor (the GPCR) to other signal transduction proteins inside the cell.

Ligand-gated Ion Channels

A transmembrane protein containing a pore that opens or closes as it changes shape in response to a signaling molecule (ligand), allowing or blocking the flow of specific ions; also called an ionotropic receptor.

local regulator

chemical signal that acts over short distances