Cell-Cell Interactions, Communication, and the Cell Cycle

Comprehensive vocabulary flashcards covering cell-cell interactions, junctions, signaling pathways, and the mechanics of the cell cycle and mitosis.

Multicellularity

The state of being composed of multiple cells which rely on physical connections and the division of labor to maintain tissue structure and function.

Anchoring junctions

Mechanically strong cell junctions that hold adjacent cells together or attach cells to the extracellular matrix (ECM).

Tight junctions

Also known as occluding junctions; these form a water-tight seal between adjacent animal cells in an epithelial layer to prevent material leakage.

Gap junctions

A cluster of channels in animal cells that permit the direct exchange of ions and small molecules between the cytosols of adjacent cells.

Middle lamella

A polysaccharide layer comprised of gelatinous pectins that cements together the cell walls of adjacent plant cells.

Plasmodesmata

Membrane-lined channels between the cell walls of adjacent plant cells that connect their plasma membranes, cytoplasm, and smooth endoplasmic reticulum.

Cadherins

$Ca^{2+}$-dependent adhering molecules that promote cell-to-cell adhesion; they connect to the cytoskeleton inside the cell via linker proteins.

Integrins

A group of cell-surface receptor proteins that create connections between cells and the ECM using an intracellular domain to bind the cytoskeleton; they do not require $Ca^{2+}$.

Connexon

A channel formed by six connexin proteins in one cell aligned with six in an adjacent cell, allowing the sharing of metabolites and direct signaling.

Symplast

A continuous network of shared cytoplasm between plant cells interconnected by plasmodesmata.

Apoplast

The extracellular space corridor in plant tissues.

Cell communication

The process of cells detecting and responding to signals in the extracellular environment to coordinate activities.

Apoptosis

The process by which signals intentionally cause a cell to undergo programmed cell death.

Auxin

The signaling molecule responsible for phototropism in plants; it accumulates in non-illuminated parts of the plant to coordinate shape changes.

Autocrine signaling

A signaling method where cells secrete molecules that bind to receptors on their own surface or on similar neighboring cells.

Paracrine signaling

A form of signaling where cells release signals that affect nearby target cells but do not affect the originating cell.

Endocrine signaling

A long-distance signaling method where hormones travel through the bloodstream to affect specific target cells.

Ligand

A signaling molecule that binds non-covalently to a receptor with high specificity, causing a conformational change.

Proteome

The complete set of proteins made by a cell, which determines how a target cell responds to a given signaling molecule.

Protein kinases

Enzymes that catalyze the transfer of a phosphate group from $ATP$ to an intracellular protein.

Receptor Tyrosine Kinases (RTKs)

A category of enzyme-linked receptors in animals that dimerize and undergo autophosphorylation upon binding a signaling molecule like growth factor.

G-protein coupled receptors (GPCRs)

Common animal receptors with $7$ transmembrane segments that activate a G protein, causing it to exchange $GDP$ for $GTP$.

Second messengers

Small molecules or ions like $cAMP$, $Ca^{2+}$, $DAG$, and $IP_3$ that relay signals inside a cell after a first messenger binds to a surface receptor.

Adenylyl cyclase

An enzyme in the plasma membrane that synthesizes $cAMP$ from $ATP$.

Phosphodiesterase

The enzyme responsible for inactivating $cAMP$ by converting it to $AMP$. It is inhibited by high doses of caffeine.

Quorum sensing

Signaling pathways in unicellular organisms that respond to population density by releasing species-specific molecules once a specific threshold is reached.

Chromosome

A single long double helix of DNA wrapped around proteins called histones.

Diploid ($2n$)

Cells containing two sets of chromosomes; in humans, this equals $23$ pairs or $46$ total chromosomes.

Haploid ($n$)

Cells containing only one member of each chromosome pair; in humans, gametes have $23$ total chromosomes.

Sister chromatids

Identical double-stranded DNA copies of a replicated chromosome attached at the centromere.

Interphase

The non-dividing phase of the cell cycle consisting of $G_1$, $S$, and $G_2$ phases, where cells grow and copy DNA.

S phase

The specific stage of interphase where DNA synthesis and chromosome replication occur.

Mitotic spindle

An apparatus composed of astral, polar, and kinetochore microtubules responsible for organizing and sorting chromosomes during mitosis.

Centrosomes

Microtubule organizing centers (MTOCs) that duplicate at the start of M phase and define the poles of the spindle.

Anaphase

The fourth phase of mitosis where connections between sister chromatids are broken and they are pulled toward opposite poles as kinetochore microtubules shorten.

Cleavage furrow

A ring of actin and myosin filaments that contracts to pinch animal cells into two daughter cells during cytokinesis.

Cell plate

A structure formed by the fusion of Golgi-derived vesicles that creates a new cell wall between two daughter plant cells.

$G_0$ state

A quiescent or resting state where non-dividing cells are arrested and perform their functions without preparing for division.