Bio Self Summary Unit 4 Test PDF

Direct Contact: - Communicate through cell junctions - Signaling substances and material dissolved in cytoplasm passes freely between cells - Animals: Gap junction - Plants: Plasmodesmata What role do gap junctions and plasmodesmata play in cell to cell communication? They allow mat...

Direct Contact: - Communicate through cell junctions - Signaling substances and material dissolved in cytoplasm passes freely between cells - Animals: Gap junction - Plants: Plasmodesmata What role do gap junctions and plasmodesmata play in cell to cell communication? They allow materials and signalling substance to pass freely from one cell to an adjacent cell Why do signaling substances pass freely through cytoplasm in direct contact? They are small, nonpolar molecules(?) Local Regulators: - Secreting cell sends a chemical message - a local regulator or ligand - that travels short distances through extracellular fluid - Chemical messages cause a response in target cell Paracrine - Secretory cells release local regulators (ex. Growth factors & hormones) via exocytosis - excretion out of cell using ATP - to an adjacent cell Synaptic - Occurs in animal nervous systems - Neurons release neurotransmitters, which diffuse across the “synaptic cleft” - the space between the nerve cell and target cell - Goes to nerves or muscles What distinguishes local signalling from long distance? Local signalling sends signals to nearby cells, further than direct contact but shorter than long distance How does the movement of ligands in paracrine signaling differ from synaptic? Paracrine signalling involves the excretion of regulators (exocytosis) to adjacent cells, while synaptic signaling releases neurotransmitters, which diffuse across the space between the nerve and the target cell. Long Distance: Hormones are used for long distance Plants: Release hormones through vascular tissue or through the air to reach target tissues Animals: Endocrine signaling - Specialized cells release hormones into the circulatory system where they reach target cells. What mechanisms allow hormones to reach their targets? Vascular tissue and bloodstreams for plants and animals, respectively Cell Signalling Steps: 1. Reception: Detection & receiving of ligand (chemical message) by a receptor in the target cell a. Receptor: Macromolecule that binds to single molecule (ligand) b. When ligand binds to receptor, receptor activates with a conformational change (change in shape of a macromolecule) i. Receptor can interact with other cellular molecules ii. Initiates a transduction signal iii. Receptors found in plasma membrane or are intracellular c. Plasma Membrane receptor i. Most common ii. Binds to ligands 1. Polar 2. Large iii. Ex GPCRs d. Intracellular i. Cytoplasm of nucleus of target cell ii. Binds to ligands that pass through plasma membrane iii. Ex. hydrophobic molecules (steroid & thyroid hormones, nitric acid) 2. Transduction: Conversion of extracellular signal -> intracellular: causes cell response a. Requires a signal transduction pathway (sequence of changes in a series of molecules) b. Signal transduction pathway regulates proteins: i. Phosphorylation: Relays signal in a cell by adding a phosphate group 1. Enzyme protein kinase ii. Dephosphorylation: Shuts off pathways by removing a phosphate group 1. Enzyme protein phosphatase c. Signal is amplified i. Second messengers: Small, non protein molecules & ions help relay the message 1. cAMP (cyclic AMP) is very common 3. Response: Final molecule in the pathway converts the signal to a response, altering cell processes. Ex: a. Proteins that alter membrane permeability b. Enzyme changing metabolic process c. Proteins turning genes on or off What happens when a ligand binds to a receptor? The receptor activates via a conformational change, which is important because such changes change the function of the ligand Signal Transduction Pathway - Influences how cell responds to its environment - Can result in changes in gene expression and cell function - Alter phenotypes or cause cell death - If receptor proteins or any component mutates, transduction will change GPCRs: G protein coupled receptors - Largest category of cell surface receptors - Animal sensory systems - Binds to a G-protein that binds to GTP (similar to ATP) - GPCR, enzyme, and G protein are inactive until ligand binding to GPCR on the extracellular side - Ligand binding -> Cytoplasmic side changes shape - G protein can now bind to GPCR - Activates both - GDP becomes GTP - Part of active G protein can bind to enzyme - Activates enzyme - Acts as amplification for cell response Ion Channels: Ligand gated ion channels: - Located in plasma membrane - Important for nervous system - Receptors act as a gate for ions - When a ligand binds to receptor, the gate opens or closes allowing for specific ion diffusion - Series of events lead to cell response