Chapter 11 Outline - Summary Campbell Biology PDF

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Chapter 11: Cell Communication 11.1 “External signals are converted into responses within the cell” Evolution of Cell Signaling

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Cells of the yeast Saccharyomes cerevisiae identify their mates by chemical signaling

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There are two mating types (sexes), called a and α. Cells of mating type a secrete a chemical signal called “a factor”, while mating type α secrete α factor

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Without actually entering the cells, the two mating factors cause the cells to grow toward each other and bring about other cellular changes. The result is fusion, or mating, of two cells of opposite type. The new a/α cell contains all of the genes of both original cells

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The process by which a signal on a cell’s surface is converted into a specific cellular response is a series of steps called a signal transduction pathway Local and Long-Distance Signaling

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Messenger molecules are secreted by the signaling cell. Some of these travel only short distances; such local regulators influence cells in the vicinity

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Both animals and plants use chemicals called hormones for long-distance signaling. Hormonal signaling in animals, AKA endocrine signaling, specialized cells release hormone molecules into vessels of the circulatory system, by which they travel to target cells in other parts of the body

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Plant hormones (growth regulators) sometimes travels in vessels but more often reach their targets by moving through cells or diffusion through the air as a gas The Three Stages of Cell Signaling: A Preview

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Cell conversation can be dissected into three stages: reception, transduction, and response

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Reception is the target cell’s detection of a signal molecule coming from outside the cell. A chemical signal is “detected” when it binds to a receptor protein located at the cell’s surface or inside the cell

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The binding of the signal molecule changes the receptor protein in some way, initiating the process of transduction

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This stage converts the signal to a form that can bring about a specific cellular response. Transduction sometimes occurs in a single step but more often requires a sequence of changes in a series of different molecules—a signal transduction pathway. The molecules in the pathway are called relay molecules

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The transduced signal finally triggers a response in the third stage. The response may be almost any imaginable cellular activity, such as catalysis by an enzyme, rearrangement of the cytoskeleton, or activation of specific genes in the nucleus 11.2 “Reception: A signal molecule binds to a receptor protein, causing it to change shape”

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A receptor protein on or in the cell allows the cell to “hear” the signal and respond to it

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The signal molecule behaves as a ligand, a molecule that specifically binds to another molecule often a larger one Intracellular Receptors

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Intracellular receptor proteins are found in either the cytoplasm or nucleus of target cells. To react such a receptor, a chemical messenger passes through the target cell’s plasma membrane Receptors in the Plasma Membrane

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Most water-soluble molecules bind to specific sites on receptor proteins embedded in the cell’s plasma membrane. Such receptors transmits information from the extracellular environment to the inside of the cell by changing shape or aggregating when a specific ligand binds to it

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3 major types: g-protein-linked receptors, receptor tyrosine kinases, and ion channel receptors

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A G-protein-linked receptor is a plasma membrane receptor that works with the help of a protein called a G protein

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A receptor tyrosine kinase can trigger more than one signal transduction pathway, at once, helping the cell regulate and coordinate many aspects of cell growth and cell reproduction. A kinase is an enzyme that catalyzes the transfer of phosphate groups

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A ligand-gated ion channel is a type of membrane receptor, a region of which can act as a “gate” when the receptor changes shape

11.3 “Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell” Signal Transduction Pathways 

The binding of a specific signal molecule to a receptor triggers the first step

The signal-activated receptor activates another protein, which activates another molecule, and so on, until the protein that produces the final cellular response is activated Protein Phosphorylation and Dephosphorylation 

An enzyme that transfers phosphate groups from ATP to a protein is a protein kinase

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Protein phosphatases are enzymes that can rapidly remove phosphate groups from proteins, a process called dephosphorylation Small Molecules and Ions as Second Messengers

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Many signaling pathways also involve small, nonprotein, water-soluble molecules or ions called second messengers. They readily spread throughout the cell by diffusion. Second messengers participate in pathways initiated by G-protein-linked receptors and receptor tyrosine kinases. Two common types are cAMP and Ca 2+ Cyclic Amp

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Adenylyl cyclase concerts ATP to cAMP in responses to an extracellular signal Calcium Ions and Inositol Triphosphate (IP3)

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Ca2+ causes many responses in animal cells, such as muscle cell contraction, secretion of certain substances, and cell division

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The pathways leading to calcium release involve still other second messengers, inositol triphosphate (IP3) and diacylglycerol (DAG). They are produced by cleavage of a certain kind of phospholipid in the plasma membrane 11.4 “Response: Cell Signaling leads to regulation of cytoplasmic activities or transcription”

Cytoplasmic and Nuclear Responses 

The final step in the signaling pathway activates the enzyme that catalyzes the breakdown of glycogen Fine-Tuning of the Response

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Signaling pathways amplify the signal and contribute to the specificity of response Signal Amplification

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Elaborate enzymes cascades amplify the cell’s response to a signal. At each catalytic step in the cascade, the number of activated products is much greater than in the preceding step

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The amplification effect stems from the fact that these proteins persist in the active form long enough to process numerous molecules of substrate before they become inactive again The Specificity of Cell Signaling

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Different kinds of cells have different collections of proteins. The response of a particular cell to a signal depends on its particular collection of signal receptor proteins, relay proteins, and proteins needed to carry out the response Signaling Efficiency: Scaffolding Proteins and Signaling Complexes

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Scaffolding proteins are large relay proteins to which several other relay proteins are simultaneously attached Termination of the Signal

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The binding of signal molecules to receptors is reversible, with the result that the lower the concentration of signal molecules, the fewer will be bound at any given moment

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When signal molecules leave the receptor, the receptor revers to its inactive form...