1. Elaborate, complex, intracellular and intercellular
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
hormones, fatty acid derivatives, dissolved gas.
Target cell, receptor, response
AH Cell Signalling

2. Tight – membranes fused preventing leakage
Direct communication
Junctions
Animal
Tight – membranes fused preventing leakage
Desmosome – filaments protrude giving linkages
between cell sheets
Gap – cytoplasmic channels so molecules can
flow between cells
Plant
Plasmodesmata – channels in adjacent
cell walls with plasma membrane lining.
Connection of cytoplasm
AH Cell Signalling

3. 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

4. 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 molecules
Ca2+ - second messengers increase in ions causes response
AH Cell Signalling

5. opening/closing of ion channels in membrane rearranging cytoskeleton
Response
Cell may respond by:
opening/closing of ion channels in membrane
rearranging cytoskeleton
synthesis or degradation of enzymes or
other proteins
change in gene expression
AH Cell Signalling

6. Extracellular hydrophobic signalling
Signals can diffuse across membrane
Examples include hormones e.g. thyroxine, sex hormones
and cortisol
Activate gene regulatory proteins
Occur in animals and plants
Ecdysone – promotes moulting in arthropods
Thyroxine – increases metabolism
Cortisol – increases release of sugars
Sex hormones – stimulate secondary sexual characteristics etc.
Slower than electrical signals but may persist for hrs/days
AH Cell Signalling

7. 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

8. Receptor proteins Enzyme linked
Give enzyme linked response (kinase) on cytoplasmic
side, activating intracellular proteins
G-protein linked receptors
Activate a GTP-binding protein (G-protein)
made of seven alpha helices.
G-protein acts as switch for enzymes in the cell
depending on binding of guanine nucletides
GDP (gives inactive form) or GTP (gives active form)
Ion-channel linked receptors
Transmembrane proteins open with a signal molecule
Allows rapid ion movement e.g. Synapses
AH Cell Signalling

9. Cell signalling in plants
Include:
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
AH Cell Signalling

10. 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
AH Cell Signalling