Unit 4: Cell Communication and Cell Cycle Practice Flashcards

Definition-based vocabulary flashcards covering the core concepts of cell communication, signaling mechanisms, feedback loops, and the cell cycle as described in the Unit 4 lecture notes.

Reception

The first stage of cell communication where a signal molecule, also known as a ligand, binds to a receptor protein, typically through a change in the receptor’s shape.

Transduction

The second stage of cell communication that involves a chain of molecular events converting an external signal into an internal message, often amplifying the signal.

Response

The final stage of cell communication where the cell undergoes a specific change in behavior, such as altered gene expression, enzyme activity, or cytoskeleton shape.

Taxis

The innate behavioral movement of an organism in response to a stimulus, which can be positive (toward the stimulus) or negative (away from the stimulus).

Chemotaxis

A specific type of taxis where an organism moves in response to chemical signals.

Signal amplification

A process where one activated protein activates many downstream molecules, allowing a small concentration of ligands to produce a significant cellular effect.

Phosphatases

Enzymes that remove phosphate groups from proteins to turn off signaling pathways and reset the cell's state.

Juxtacrine signaling

Direct contact signaling between cells that touch, occurring through cell junctions or membrane-bound ligands.

Gap junctions

Channels in animal cells that allow ions and small molecules to pass directly between the cytoplasms of neighboring cells.

Plasmodesmata

Channels between plant cells that enable the direct movement of molecules between them.

Paracrine signaling

A form of local signaling where cells secrete regulators, such as growth factors or cytokines, that diffuse short distances to affect nearby cells.

Synaptic signaling

A specialized local signaling mechanism in neurons where neurotransmitters are released into a synapse to target a specific nearby cell.

Endocrine signaling

Long-distance signaling where glands release hormones into the bloodstream in animals or transport tissues in plants to reach distant target cells.

Autocrine signaling

A signaling mechanism where a cell releases a signal that binds to receptors on its own surface or on the same cell type.

Ligand-gated ion channel

A membrane receptor that opens or closes in response to ligand binding, allowing ions to flow down their electrochemical gradients.

Receptor tyrosine kinase (RTK)

An enzyme-linked membrane receptor that, upon ligand binding, undergoes dimerization and autophosphorylation to activate multiple relay proteins.

G protein-coupled receptor (GPCR)

A membrane receptor that activates a G protein by switching it between GDP- and GTP-bound states to trigger downstream effects.

Second messenger

A small, non-protein molecule or ion, such as $cAMP$ or $Ca^{2+}$, that relays and amplifies a signal inside the cytoplasm.

Apoptosis

A regulated and programmed cell death process involving a cascade of proteases called caspases, leading to cell fragmentation and removal.

Negative feedback

A regulatory pattern that reduces the initial stimulus to stabilize a system around a set point, also known as feedback inhibition.

Positive feedback

A regulatory mechanism that increases the initial stimulus, pushing a biological process forward until a clear endpoint is reached.

Sister chromatids

Two identical copies of a duplicated chromosome produced during $S$ phase and held together by a centromere.

Mitosis

The phase of the cell cycle dedicated to nuclear division, ensuring each daughter cell receives an identical set of chromosomes.

Cytokinesis

The division of the cytoplasm that follows mitosis, occurring via a cleavage furrow in animal cells and a cell plate in plant cells.

Cyclin-dependent kinases (CDKs)

Kinases that are stable in concentration and must bind to fluctuating regulatory proteins called cyclins to drive the cell cycle forward.