introduction
DESCRIPTION
Introduction. Elaborate, complex, intracellular and intercellular. Animal cells complex system of proteins e.g. Receptor proteins (surface and intracellular) Protein kinases Protein phosphatases GTP-binding proteins (G-proteins). Signal molecules include proteins, nucleotides, steroid - PowerPoint PPT PresentationTRANSCRIPT
AH Cell Signalling
Introduction
Elaborate, complex, intracellular and intercellular
Animal cells complex system of proteins e.g.•Receptor proteins (surface and intracellular)•Protein kinases•Protein phosphatases•GTP-binding proteins (G-proteins)
Signal molecules include proteins, nucleotides, steroidhormones, fatty acid derivatives, dissolved gas.
Target cell, receptor, response
AH Cell Signalling
Direct communication
AnimalTight – membranes fused preventing leakageDesmosome – filaments protrude giving linkages between cell sheetsGap – cytoplasmic channels so molecules canflow between cells
PlantPlasmodesmata – channels in adjacent cell walls with plasma membrane lining.Connection of cytoplasm
Junctions
AH Cell Signalling
Stages of cell signalling
Reception – transduction – response
Signal reception
•Specific•target protein(receptor)•Signal molecule called ligand•Change in shape of receptor protein•Local or distant effects•3 main types of membrane receptors enzyme linked, G-protein linked and Ion-channel linked.
AH Cell Signalling
Signal transduction (transfer of signal within cell)
•Staged in signal transduction pathway•Allows amplification•Activates large numbers of molecules•Cascade of molecular events
Molecules involved
Protein kinases - phosphorylate proteins, cascade ATP into ADP to activate proteins.
Cyclic AMP – second messenger small non protein moleculesCa2+ - second messengers increase in ions causes response
AH Cell Signalling
Response
Cell may respond by:
•opening/closing of ion channels in membrane
•rearranging cytoskeleton
•synthesis or degradation of enzymes orother proteins
•change in gene expression
AH Cell Signalling
Extracellular hydrophobic signalling
Signals can diffuse across membrane
Examples include hormones e.g. thyroxine, sex hormonesand cortisol
Activate gene regulatory proteins
Occur in animals and plantsEcdysone – promotes moulting in arthropodsThyroxine – increases metabolismCortisol – increases release of sugarsSex hormones – stimulate secondary sexual characteristics etc.
Slower than electrical signals but may persist for hrs/days
AH Cell Signalling
Extracellular hydrophillic cell signalling
Act on surface of plasma membrane to induce a response inside cells.
3 main types of receptor:
•enzyme linked receptors
•G-protein-linked receptors
•ion-channel-linked receptors
AH Cell Signalling
Receptor proteins
Enzyme linkedGive enzyme linked response (kinase) on cytoplasmicside, activating intracellular proteins
G-protein linked receptorsActivate a GTP-binding protein (G-protein) made of seven alpha helices.G-protein acts as switch for enzymes in the celldepending on binding of guanine nucletidesGDP (gives inactive form) or GTP (gives active form)
Ion-channel linked receptorsTransmembrane proteins open with a signal moleculeAllows rapid ion movement e.g. Synapses
AH Cell Signalling
Cell signalling in plants
Auxins (IAA) – promotes elongation of shoots
Cytokinins – stimulate cytokinesis
Gibberellins – stimulate stem elongation and germination
Abscisic acid (ABA) – promotes abscission
Ethylene – gas that inhibits fruit ripening
Include:
AH Cell Signalling
Stages in plant cell signalling
Reception – transduction - responses
Signals involve light, gravity, touch, water
Responses include tropisms, general growth, flower/fruit production, leaf/fruit abscission