AP Biology Unit 4: Signal Transduction and the Cell Cycle

Cell Communication

The process through which cells interact with their environment and other cells to maintain homeostasis.

Evolutionary Significance

The reason signal transduction pathways are conserved across species, indicating a common ancestor.

Juxtacrine signaling

A mode of cell communication that requires direct contact between cells.

Paracrine signaling

Cellular signaling that involves the release of signals into the extracellular fluid to affect nearby cells.

Autocrine signaling

Communication in which a cell secretes a signal that binds to receptors on its own surface.

Endocrine signaling

Long-distance signaling where hormones are transported through the circulatory system to target cells.

Taxis

Movement of unicellular organisms toward or away from a stimulus.

Chemotaxis

Movement of bacteria toward a chemical (food) or away from a harmful substance (toxin).

Quorum Sensing

A process by which bacteria communicate based on population density to coordinate group behaviors.

Signal Transduction

The conversion of an external signal into a functional cellular response.

Reception

The detection of a signaling molecule by a cell's receptor.

Ligand

A specific signaling molecule that binds to a receptor.

Conformational change

The alteration in shape of a receptor when a ligand binds to it.

G-Protein Coupled Receptors (GPCRs)

The largest family of cell-surface receptors involved in signal transduction.

Ligand-Gated Ion Channels

Receptors that open in response to ligand binding to allow ions to flow through.

Intracellular Receptors

Receptors located in the cytoplasm or nucleus that bind hydrophobic ligands.

Signal Amplification

The process by which a single ligand activates multiple target molecules.

Phosphorylation Cascade

A series of reactions where proteins are sequentially phosphorylated to relay a signal.

Protein Kinase

An enzyme that adds phosphate groups to proteins, activating them.

Protein Phosphatase

An enzyme that removes phosphate groups from proteins, deactivating them.

Second Messengers

Small molecules that relay signals within a cell.

Cyclic AMP (cAMP)

A second messenger created from ATP, involved in signaling pathways.

Calcium Ions (Ca^2+)

Important second messengers involved in various cellular functions.

Nuclear Response

Cellular responses that occur in the nucleus, often involving gene expression.

Cytoplasmic Response

Responses that occur in the cytoplasm, involving enzymatic activity or ion channels.

Apoptosis

Programmed cell death essential for development and maintaining tissue homeostasis.

Negative Feedback

A mechanism that reduces the output of a system to maintain homeostasis.

Positive Feedback

A mechanism that amplifies a physiological process or condition.

Cell Cycle

The sequence of events from the formation of a cell to its division.

Interphase

The phase of the cell cycle where the cell grows and prepares for division.

G1 Phase (First Gap)

The first phase of interphase where the cell grows and performs normal functions.

S Phase (Synthesis)

The phase where DNA replication occurs, making duplicates of chromosomes.

G2 Phase (Second Gap)

The final phase of interphase where the cell prepares for mitosis.

M Phase

The phase of the cell cycle where mitosis and cytokinesis occur.

Prophase

The stage of mitosis where chromosomes condense and the nuclear envelope breaks down.

Metaphase

The stage of mitosis where chromosomes align at the metaphase plate.

Anaphase

The stage of mitosis where sister chromatids are pulled apart to opposite poles.

Telophase

The stage of mitosis where two new nuclei form around the separated chromosomes.

Cytokinesis

The division of the cytoplasm to form two separate daughter cells.

G1 Checkpoint

A control point that checks cell size, nutrients, and DNA integrity.

G2 Checkpoint

A control point that ensures DNA replication occurred correctly.

M Checkpoint

A checkpoint during mitosis that ensures all chromosomes are properly attached to spindle fibers.

Cyclins

Proteins that regulate the timing of the cell cycle by fluctuating in concentration.

Cyclin-Dependent Kinases (CDKs)

Enzymes that regulate the cell cycle when activated by cyclins.

MPF (Maturation-Promoting Factor)

A Cyclin-CDK complex that promotes entry into M phase.

Cancer

A disease characterized by uncontrolled cell division and growth.

Proto-oncogenes

Normal genes that promote cell growth; mutations can convert them to oncogenes.

Tumor-Suppressor Genes

Genes that inhibit cell division; mutations can disable their function, leading to cancer.

p53

A tumor-suppressor gene that regulates the cell cycle and initiates apoptosis if DNA damage is detected.