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

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 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.

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

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