Campbell Biology Chapter 11: Cell Communication

Comprehensive vocabulary flashcards covering the concepts, mechanisms, receptors, cascades, and pathways of cell signaling and apoptosis from Campbell Biology, Chapter 11.

Signal Transduction Pathway

A series of sequential molecular steps by which a signal received at a cell's surface is converted into a specific cellular response.

Yeast Mating Types ($a$ and $\alpha$)

Two distinct cell types of yeast that identify each other by secreting specific mating factors that bind to receptors on the opposite cell type, leading to cell fusion.

Cell Junctions

Specialized connections (gap junctions in animal cells and plasmodesmata in plant cells) that directly connect the cytoplasm of adjacent cells, allowing signaling substances to pass freely.

Paracrine Signaling

A form of local signaling in animal cells where a cell secretes messenger molecules, such as growth factors, that travel short distances through extracellular fluid to stimulate nearby target cells.

Growth Factors

A class of local regulator molecules in animals that stimulate nearby target cells to grow and divide.

Synaptic Signaling

A specialized type of local signaling occurring in the animal nervous system where an electrical signal moving along a nerve cell triggers the release of neurotransmitter molecules across a synapse to a target cell.

Hormones

Chemical messengers utilized by both plants and animals for long-distance signaling.

Endocrine Signaling

Hormonal long-distance signaling in animals where specialized endocrine cells release hormones into body fluids, specifically the circulatory system, to reach distant target cells.

Reception

The initial stage of cell signaling wherein a target cell detects a signaling molecule from outside the cell as it binds to a specific receptor protein.

Transduction

The second stage of cell signaling, in which the binding of a signaling molecule alters the receptor protein and initiates a signal transduction pathway, often occurring across a cascade of steps.

Output Response

The third and final stage of cell signaling, in which the transduced signal triggers a specific cellular activity, such as enzyme regulation or gene transcription.

Ligand

A molecule that specifically binds to another molecule, typically a larger receptor protein, usually causing the receptor protein to undergo a shape change.

G Protein-Coupled Receptor (GPCR)

A cell-surface transmembrane receptor that works with the assistance of a G protein, constituting the largest family of cell-surface receptors.

G Protein

A relay protein bound to the plasma membrane that binds the energy-rich molecule GTP and acts as a molecular switch, cycling between active (GTP-bound) and inactive (GDP-bound) states.

Receptor Tyrosine Kinase (RTK)

A plasma membrane receptor protein that exhibits enzymatic activity, forming a dimer upon ligand binding and transferring phosphate groups from ATP to tyrosines, enabling the simultaneous activation of multiple relay pathways.

Ligand-Gated Ion Channel

A transmembrane receptor containing a region that acts as a gate, opening or closing to regulate the passive flow of specific ions (such as $\text{Na}^+$ or $\text{Ca}^{2+}$) in response to the binding of a specific ligand.

Intracellular Receptors

Receptor proteins located within the cytoplasm or nucleus of target cells that are activated by small or hydrophobic chemical messengers, such as steroid and thyroid hormones, capable of crossing the plasma membrane.

Transcription Factor

A specialized protein that controls gene expression by determining which genes are transcribed into mRNA; activated intracellular hormone-receptor complexes often act as transcription factors.

Protein Kinase

An enzyme that transfers phosphate groups from ATP to a target protein, a regulatory modification termed phosphorylation.

Phosphorylation Cascade

A series of chemical reactions in a transduction pathway where one active protein kinase phosphorylates and activates another kinase, propagating and amplifying the signal.

Protein Phosphatase

An enzyme that rapidly removes phosphate groups from proteins (dephosphorylation), acting as a molecular switch to inactivate protein kinases and turn off signaling pathways.

Second Messenger

A small, nonprotein, water-soluble molecule or ion, such as cyclic AMP or $\text{Ca}^{2+}$, that rapidly diffuses throughout the cytoplasm to relay signals from activated receptors.

Cyclic AMP (cAMP)

A ring-shaped second messenger synthesized from ATP by adenylyl cyclase that commonly functions by activating protein kinase A.

Adenylyl Cyclase

An enzyme embedded in the plasma membrane that converts ATP into cyclic AMP (cAMP) and pyrophosphate in response to an extracellular signal transmitted by a G protein.

Inositol Triphosphate ($\text{IP}_3$)

A second messenger produced by the cleavage of a plasma membrane phospholipid (PIP2) that diffuses to the endoplasmic reticulum and binds to ligand-gated calcium channels to release $\text{Ca}^{2+}$ into the cytosol.

Diacylglycerol (DAG)

A second messenger produced alongside $\text{IP}_3$ by the cleavage of a specific membrane phospholipid in the plasma membrane.

Scaffolding Protein

A large relay protein to which several other relay proteins (such as multiple protein kinases) are simultaneously attached, greatly enhancing signal transduction speed and efficiency.

Apoptosis

A programmed cellular suicide mechanism wherein damaged, infected, or aged cells are systematically dismantled, packaged into membrane-bound vesicles, and cleared by scavenger cells to protect neighboring tissues.

Caspases

The main group of approximately $15$ proteases (enzymes that break down proteins into smaller peptides/single amino acids) in humans and other mammals that execute apoptosis by cleaving specific cellular proteins during apoptosis.