AP biology 1-6

Chapter 15: Cell Signaling and Signal Transduction

15.1 Basic Elements of Cell Signaling Systems

• Cell signaling allows cells to communicate and coordinate activities.

• Extracellular messengers play a key role in signaling pathways.

• Types of signaling:

  • Autocrine signaling: Cell releases a signal that affects itself.

  • Paracrine signaling: Signal affects nearby cells.

  • Endocrine signaling: Signals (hormones) are transmitted through the bloodstream to distant cells.

• Receptor expression determines a cell's response to signals.

15.2 Overview of Extracellular Messengers

• Types of messengers include:

  • Amino acids and derivatives (neurotransmitters, hormones).

  • Gases (e.g., Nitric Oxide).

  • Steroid hormones.

  • Eicosanoids (involved in various physiological processes).

  • Proteins and peptides involved in several cellular processes.

15.3 G Protein-Coupled Receptors (GPCRs)

• GPCRs are integral membrane proteins involved in transmitting signals via G proteins.

• GPCRs initiate signaling by binding ligands, activating intracellular pathways.

• Signaling pathways activated by GPCRs include increases in cAMP levels, leading to diverse cellular responses.

15.4 Protein-Tyrosine Phosphorylation in Signal Transduction

• Protein-tyrosine kinases (PTKs) regulate important cellular functions (cell growth, differentiation).

• RTKs typically dimerize upon ligand binding, activating their kinase activity and leading to phosphorylation of tyrosine residues.

• Key substrates include IRS proteins that relay signals downstream after activation by phosphorylation.

15.5 Role of Calcium as an Intracellular Messenger

• Calcium (Ca2+) is crucial for processes like muscle contraction and neurotransmission.

• Fluctuations in cytosolic calcium levels mediate various cellular responses.

• Calcium signaling can be initiated by various pathways involving GPCRs or RTKs.

15.6 Convergence, Divergence, and Cross-Talk

• Convergence: Different signals activate common pathways.

• Divergence: Signals from the same molecule can lead to different responses.

• Cross-talk: Interactions between different signaling pathways enhance cellular response versatility.

15.7 Role of Nitric Oxide (NO) as a Messenger

• NO acts both as an extracellular and intracellular messenger.

• Synthesized from L-arginine, it activates guanylyl cyclase to produce cGMP, affecting smooth muscle relaxation and other processes.

15.8 Apoptosis (Programmed Cell Death)

• Apoptosis is a regulated process eliminating damaged or unneeded cells; involves chromatin fragmentation and cell shrinkage.

• Dissintegration leads to the formation of apoptotic bodies that are engulfed by phagocytes, preventing inflammation.

• Triggered by external (e.g., TNF binding to receptors) or internal stimuli (cellular damage). URL

• Execution requires caspases, activated by either extrinsic or intrinsic pathways.

Summary Points

• Understanding cell signaling pathways is essential for grasping how cells coordinate responses to their environmental cues, impacting development, immune response, and disease.