Cell Communication Ch. 11 AP Bio

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Why is cell-to-cell communication essential for multicellular organisms?

It allows cells to coordinate activities, respond to stimuli, and regulate complex processes like growth, reproduction, and homeostasis.

What is a signal transduction pathway?

A series of steps converting a signal on the cell surface into a specific cellular response.

What does the yeast mating example demonstrate about signaling?

That signaling is evolutionarily conserved; signaling systems were present in early organisms like yeast.

What is quorum sensing?

Bacterial communication where cells detect local density using secreted signaling molecules.

What are the two kinds of local signaling?

Paracrine signaling and synaptic signaling.

What type of signaling uses hormones?

Long-distance endocrine signaling.

What are cell junctions and what do they allow?

Direct connections between cells (gap junctions/plasmodesmata) that allow molecules to pass freely.

What are the three stages of cell signaling?

Reception, transduction, and response.

What is a ligand?

A signaling molecule that binds specifically to a receptor.

What activates a G protein?

The exchange of GDP for GTP when the receptor is activated.

What type of membrane receptor is the most common in eukaryotes?

GPCRs.

What makes RTKs unique compared to GPCRs?

They can trigger multiple signal transduction pathways simultaneously.

What occurs when RTKs bind their ligand?

They dimerize and autophosphorylate tyrosine residues.

How do ligand-gated ion channels work?

Ligand binding opens the channel, allowing specific ions (Na⁺, Ca²⁺) to flow through.

What types of molecules bind intracellular receptors?

Small or hydrophobic molecules such as steroid hormones.

What is the function of a hormone–receptor complex?

Acts as a transcription factor to activate gene expression.

Why do signaling pathways often involve many steps?

Amplification of the signal and increased regulation opportunities.

What enzymes carry out phosphorylation?

Protein kinases.

What enzymes reverse phosphorylation?

Protein phosphatases.

What are second messengers?

Small, non-protein molecules that spread signals through the cell (e.g., cAMP, Ca²⁺, IP₃).

What enzyme creates cAMP?

Adenylyl cyclase converts ATP → cAMP.

What does cAMP usually activate?

Protein kinase A (PKA).

Why is Ca²⁺ an important second messenger?

Cells maintain very low cytosolic Ca²⁺, so small increases have strong effects.

What types of responses can signaling trigger?

Transcription changes in the nucleus or enzyme activity changes in the cytoplasm.

What is a transcription factor?

A protein that regulates gene expression.

How does epinephrine cause glycogen breakdown?

Through a GPCR → cAMP pathway → PKA activation → phosphorylation cascade → glycogen breakdown enzyme activation.

What are two advantages of multi-step pathways?

Signal amplification and increased specificity.

What are scaffolding proteins?

Proteins that hold multiple signaling components together, increasing efficiency.

How do cells terminate signals?

Receptors revert to inactive states once ligands detach.

What is apoptosis?

Programmed cell death involving controlled dismantling of the cell.

Why is apoptosis important?

Prevents damage to neighboring cells and is essential for development (e.g., removing webbing between fingers).

What enzymes carry out apoptosis?

Caspases.

What triggers apoptosis?

External death signals, DNA damage, or protein misfolding.

What does the C. elegans apoptosis pathway illustrate?

Balance of proteins that either promote or inhibit programmed cell death.