Lecture 02 - Second Messenger and Membranes

Lecture 02 - Second Messenger and Membranes - Lecture 2...

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Lecture 2 – Transport and Membranes Phosphatidyl-Inositol Second Messenger System (Fig 5.17b) 1. A messenger binds to a receptor on the cell membrane, activating a G protein. 2. The G protein releases the alpha subunit, which binds to and activates the enzyme phospholipase C. 3. Phospholipase C catalyzes the conversion of PIP 2 to DAG and IP 3 , each of which functions as a second messenger. 4. DAG remains in the membrane and activates protein kinase C, which catalyzes the phosphorylation of a protein. The protein brings about a response in the cell. 5. Meanwhile, IP3 moves to the cytosol and triggers the release of Ca 2+ from the endoplasmic reticulum. 6. Ca 2+ act as third messengers. They bind to a protein called calmodulin, which activates a protein kinase that phosphorylates a protein that produces a response in the cell. G Protein Control of Ion Channel Opening and Closing (Fig 5.15) 1. A messenger binds to a receptor on the cell membrane, activating a G protein. 2. The G protein releases the β subunit, which binds to an ion channel. 3. The channel either opens or closes, either allowing or stopping the flow of ions across the membrane. 4. This channel is not ligand-gated, and the response is fairly slow. Changing Electrical Properties of Cells Through Opening Ligand-Gated Channels (Fig 5.12a) 1. A messenger binds to a receptor site on an ion channel, causing it to open. 2. This process occurs instantaneously because the channel is ligand-gated. As soon as the messenger attaches, the channel opens. 3. The movement of ions into and out of the cell changes its electrical properties. Changing Cytosolic Ca 2+ Levels Through Ligand-Gated Channels (Fig 5.12b) 1. A messenger binds to a receptor site on a Ca 2+ channel, causing it to open. 2. Ca 2+ acts as a second messenger, causing various changes within the cell. 3. These responses include changes in electrical properties, muscle contraction and secretion. 4. Ca 2+ binds to calmodulin. This complex activates protein kinase. 5. Protein kinase affects various protein activities, which cause further changes within the cell. Enzyme-Linked Receptor
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This note was uploaded on 04/29/2008 for the course CELL BIO & 356 taught by Professor Merrill during the Spring '08 term at Rutgers.

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Lecture 02 - Second Messenger and Membranes - Lecture 2...

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