Cell Communication Chapter 11 11/17/2018 11:51 PM © 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

YOU MUST KNOW The 3 stages of cell communication: reception, transduction, and response How a receptor protein recognizes signal molecules and starts transduction How a cell signal is amplified by a phosphorylation cascade An example of a second messenger and its role in a signal transduction pathway How a cell response in the nucleus turns on genes, whereas in the cytoplasm it activates enzymes What apoptosis means and why it is important to normal functioning of multicellular organisms

3 stages of cell signaling Reception – the target cell detects a signal molecule coming from outside the cell Transduction – the signal is converted to a form that can bring about a specific cellular response Response – the cell responds in a specific way

Reception Ligand & Receptor Ligand is the signal molecule Receptor is what it binds to Very specific – think lock & key again Often a conformational change in receptor when ligand bind (think induced-fit model of enzymes)

Types of Receptors Intracellular receptors – found in the cytoplasm or nucleus Requires that the signal molecule crosses the cell membrane – means it must be hydrophobic Ex. steroid hormones Plasma membrane receptors – membrane proteins Bind water-soluble ligands

G-protein coupled receptors Membrane receptor that works with the help of a G protein Inner membrane proteins that bind GDP/GTP

Ligand binds to GPCR which causes a conformational change to the receptor Enables receptor to bind an inactive G protein Results in GTP losing a phosphate - exergonic reaction that provides energy and results in GDP These events activate the G protein

2. The G protein binds to an enzyme (specific!) and activates it This triggers the next step in the pathway which leads to a cellular response *All conformational changes are temporary – in order for response to continue, new ligand molecules are required

Receptor tyrosine kinases 2-part membrane proteins

Ligand bonds to receptor Results in the formation of a dimer (molecular complex in which two identical molecules are bound together)

2. Each tyrosine binds a phosphate from an ATP (requires 6 ATP molecules)

3. Binding of phosphates activates receptor proteins and initiates a cellular response for each of the tyrosines One ligand results in multiple cellular responses

Ligand-gated ion channels Specific ligand can cause ion channels in membrane to open or close Allows for facilitated diffusion to occur Change in ion concentration results in a change in cell activity

Transduction Relays signal from receptor to target Often involves several steps

Phosphorylation Cascade Phosphorylation cascade – allows for amplification of the signal (1 ligand can result in the response happening many times Each step in the signal-transduction pathway involves enzymes call protein kinases One protein kinase phosphorylates the next, causing a chain reaction in which thousands of protein kinases are activated

Protein phosphatases Protein phosphatases – enzymes that remove phosphate groups Inactivates protein kinases and therefore turns off the signal

Secondary Messengers Non-protein, water-soluble molecules or ions Once activated, can initiate a phosphorylation cascade Examples – calcium ions in muscle contractions or cyclic AMP which activates protein kinases

Response In the nucleus, response is a regulation of protein synthesis by turning genes on/off For example, the final activated molecule can be a transcription factor (proteins that regulate transcription – making mRNA from DNA to use for protein synthesis)

In the cytoplasm, regulate protein function Regulate enzyme activity by having the final activated molecule be a coenzyme or an inhibitor Opening/closing of ion channels

Apoptosis (Programed Cell Death) Cell suicide – the cell is dismantled and digested Protects neighboring cells – otherwise dying cell could release digestive enzymes Essential for vertebrate development, nervous system function, immune system function, and morphogenesis ***Molecules/components are recycled***