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Chapter 7

Chapter 7: Cell Communication and Multicellularity

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CAS BI 108
Francis Monette

BI108 Chapter 7 Notes: Cell Communication and Multicellularity 7.1: Signals and Cellular Response Cells process information. This information can be in the form of a physical stimulus or a chemical stimulus. Information may come from outside the cell or from another cells. • To respond to a signal, a cell must have a specific receptor that can detect it and a way to use that information to influence cellular processes Signal Transduction Pathway: a sequence of molecular events and chemical reactions that lead to a cell’s response to a signal Involve: 1. Signal 2. Receptor 3. Response Cells receive signals from the physical environment and from other cells • For cells deep inside multicellular organism: chemical signals are made in one part of the body and arrive at target cells by local diffusion or by circulation in the blood/plant vascular system Autocrine: signals diffuse to and effect cells that make them; ex-tumor cells because they make and respond to signals that stimulate cell division Juxtacrine: signals affect only cells adjacent to the cell producing the signal; ex-development Paracrine: signals diffuse to and affect nearby cells; ex-neurotransmitter made by one nerve cell that diffuses to nearby cell and stimulates it Hormones: signals that travel through the circulatory system in animals or vascular system of plants Asignal transduction pathway involves a signal, a receptor, and responses For information from signal to be transmitted to cell, the target cell must be able to receive the signal and respond to it. This is the job of the receptors. Signal Transduction Pathway 1. Signal BI108 Chapter 7 Notes: Cell Communication and Multicellularity 2. Receptor 3. Response • Only cells with the appropriate receptors can respond • The “response” can involve: Enzymes: catalyze biochemical reactions Transcription factors: proteins that turn expression of particular genes on and off *These are regulated: either activated or inactivated to bring about cellular change • Activity of protein can be regulated by mechanisms that control its location:  Transcription factor in the nucleus is inactive because it is separated from genetic info in nucleus  Signal transduction pathway may result in transport of the factor to the nucleus where it can affect gene expression Crosstalk: interactions between different signal transduction pathways  Asignal activated protein might activate enzymes or transcription factors in multiple pathways, leading to multiple response to a single stimulus  Result in activation of one pathway, and the inhibition of another 7.2: Signal Receptors Initiate Cellular Response Acell is bombarded with signals. But, it only responds to some of them. No cell makes receptors for all signals. Thus, a receptor protein recognizes its signal very specifically. Receptors that recognize chemical signals have specific binding sites Ligands are molecules that bind to a receptor site on another molecule. The ligand fits into a 3D site on the receptor protein.  Binding of the ligand causes the receptor protein to change its 3D shape, and thus a conformational change initiates a cellular response.  The ligand’s role is only to “knock on the door,” hence initiates The sensitivity of a cell to a signal is determined by the affinity of the cell’s receptors for the signal ligand Receptors (R) bind to their Ligands (L): BI108 Chapter 7 Notes: Cell Communication and Multicellularity For most ligand-receptor complexes (RL), equilibrium is to the right—binding is favored. When equilibrium is reached, the r
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