Cell Signalling Cellcell communication AH Biology Unit 1

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

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.

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

Communication • Transmitting – signalling cell • Receiving – target cell • Signal transduction • response

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

hormones • Adrenalin • Insulin

Local mediators • Histamine • Nitric oxide • Epidermal Growth Factor

Neurotransmitters • Acetyl Choline • GABA

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.

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

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

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

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.

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

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

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

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