1 Cell-Cell Interactions Chapter 7

2 Outline Cell Signaling Receptor Proteins – Intracellular Receptors – Cell Surface Receptors Initiating the Intracellular Signal Amplifying the Signal Expression of Cell Identity Intercellular Adhesion

3 Cell Signaling Receptor proteins have a three-dimensional shape that fits a specific signal molecule. – When a signal molecule and receptor protein bind, a change in the receptor protein is induced and a response in the cell is generated.  investigation tools  immunochemistry  molecular genetics

4 Cell Signals Direct contact Paracrine signaling Endocrine signaling – hormones Synaptic signaling – neurotransmitters

5 Cell Signaling

6 Intracellular Receptors Intracellular receptors are located within the cell, and trigger a variety of responses, depending on the receptor. – acting as gene regulators – acting as enzymes

7

8 Cell Surface Receptors Extracellular signals converted to intracellular – chemically-gated ion channels  open or close when signal molecules bind to the channel – enzyme receptors  usually activate intracellular proteins by phosphorylation – G-protein receptors  activate intermediary protein

9 Cell Surface Receptors

10 Initiating the Intracellular Signal Second messengers relay messages from receptors to target proteins. – cAMP – calcium

11

12 Amplifying the Signal Most signaling molecules exist in such low concentration, diffusion across the cytoplasm requires amplification. – A single cell surface receptor can stimulate a cascade of protein kinases to amplify the signal.  causes a strong response inside the cell to a weak signal outside

13 Signal Amplification

14

15 Expression of Cell Identity Cells contain an array of marker proteins located on the cell surface. – glycolipids - tissue-specific cell surface markers – MHC proteins - identify self versus non- self cells

16 Intercellular Adhesion Cell junctions are long-lasting or permanent connections with each other. – tight junctions - connect plasma membranes of adjacent cells in a sheet, preventing small molecules from leaking between the cells

17 Intercellular Adhesion – anchoring junctions - mechanically attach the cytoskeleton of a cell to the cytoskeletons of other cells or the extracellular matrix – communicating junctions - chemical or electrical signal passes directly from one cell to an adjacent cell  gap junctions - animals  plasmodesmata - plants

18 Cell Junctions

19 Summary Cell Signaling Receptor Proteins – Intracellular Receptors – Cell Surface Receptors Initiating the Intracellular Signal Amplifying the Signal Expression of Cell Identity Intercellular Adhesion

20