1. Cell-cell communication AH Biology Unit 1:- cell and molecular biology
Cell Signalling
Cell-cell communication
AH Biology
Unit 1:- cell and molecular biology
Look a signal

2. What the arrangements say
Extracellular hydrophobic signalling molecules
illustrated by steroid hormones eg testosterone.
These diffuse across the plasma membrane of the target cell and activate gene regulatory proteins which regulate the transcription of specific genes.
Extracellular hydrophilic signalling molecules
illustrated by peptide hormones eg insulin and neurotransmitters eg noradrenalin and acetylcholine.
These activate receptor proteins on the surface of the target cell.
The receptors act as transducers, converting the extracellular binding event into intracellular signals which alter the behaviour of the target cell.

3. Learning Objectives Explain the sequence of events in cell signalling
To distinguish between extra-cellular hydrophobic signalling and extra-cellular hydrophilic signalling
To describe the three main types of cell surface receptors
To be able to give responses induced in cells that receive a signal.

4. Communication Transmitting – signalling cell Receiving – target cell
Signal transduction
response

5. Systems of Communication
Endocrine
Secretion of hormone into bloodstream
Panacrine
Local mediator secreted which can affect cells in immediate area
Neuronal
Neurones elicit responses by release of neurotransmitter at synapses
Contact dependent

6. hormones
Adrenalin
Insulin

7. Local mediators
Histamine
Nitric oxide
Epidermal Growth Factor

8. Neurotransmitters
Acetyl Choline
GABA

9. Extra-cellular hydrophobic signalling molecules
Small hydrophobic molecules enter cell by diffusion and attach to receptor proteins.
Steroid hormones
Cortisol
Testosterone
Thyroid hormones
Thyroxine
Activate gene regulatory proteins in the cell, which stimulates transcription of genes.

10. Extra-cellular hydrophilic signalling molecules
Molecules too large or too hydrophilic to cross membrane
Cell surface transmembrane receptors
Ion-channel-linked
Enzyme-linked
G-protein-linked

11. Ion-channel-linked AKA chemically-gated ion channels How they work
Open pores through protein in response to binding of signal molecule
Ions flow through gate generating an electrical effect

12. Enzyme-linked Generate enzyme activity on cytoplasmic end of protein
Kinase activity causes phosphorylation of other intracellular proteins

13. G-protein-linked
Activate GTP-binding site (the G protein) this sets off a chain of events in the cell.
All have same structural arrangement in membrane – seven-pass transmembrane protein.
Activated G protein diffuses away from receptor protein site and activates its target protein.

14. Target Proteins (of G-protein)
Ion channel protein
Enzyme
Adenylate cyclase
Phospholipase C
These enzymes catalyse formation of secondary messengers

15. Secondary Messengers
Trigger intracellular response to original signal transduction event at cell surface.
Adenylate cyclase – generates cyclic AMP
Phospholipase C – generates inositol triphosphate

16. Cell Signalling
Cells are constantly engaged in the exchange of information in the form of molecular signals
This enables cells in multi-cellular systems to function in an integrated way

17. Give an account of reception of molecular signals in cells
Essay Question – 15 marks
Give an account of reception of molecular signals in cells