BIO1140 Chapter 7a - Function of Membranes

BIO1140 Chapter 7a - Function of Membranes - Cellular...

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Cellular Biology Chapter 7 – Membranes: Their structure, function, and chemistry Function of Membranes Membranes define the boundaries of the cell & Serves as Permeability Barriers Interior must be physically separated from exterior in order to keep desirable substances in and undesirable substances out Able to do this due to the hydrophobic interior of the membrane Outside membrane – plasmalemma or plasma membrane - Regulates the passage of materials in/out of the cell Inner membranes (surrounding vacuoles, etc.) – intracellular membranes - Serves to compartmentalize functions (within eukaryotic cells) Membranes are Sites of Specific Proteins therefore Specific Functions Specific proteins on membrane = specific membrane functions Best way to characterize membrane is by enzymes, transport proteins, and receptors associated with it - Distinctive enzymes on mitochondria, chloroplasts, ER, peroxisomes, etc. Membrane Proteins Regulate the Transport of Solutes Regulate the transport of substance in and out of the cell Can be indicated by several manners - Concentration gradient - Electrochemical potential - Simple diffusion - Facilitated diffusion (transport proteins) - Active transport - direct ATP - indirect uses electrochemical potential of sodium coupled with ATP - Endocytosis - Exocytosis Membrane Proteins Detect and Transmit Electrical and Chemical Signals Membrane proteins allow cells to recognize, transmit, and repond to a variety of specific chemical signals Signal transduction: the detection of specific signals at the outer surface of cells and the specific mechanisms used to transmit the signal the cell interior - Steroid hormones: diffuses because it is nonpolar and interacts with regulatory proteins - Receptors: signals do not enter cell but bind onto the specific protein (receptor) on the outer surface of the plasmalemma. This uses a second messenger system (internal signasl) Membrane Proteins Mediate Cell Adhesion and Cell-to-Cell communication Cells are in contact with each other via direct cytoplasmic connections that allow some exchange of cellular components
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Cellular Biology Chapter 7 – Membranes: Their structure, function, and chemistry Animal cells = gap junctions Plant cells = Plasmodesmata Interactions with extracellular Material Cell membrane – cell wall Cell to cell connections – tight junctions Cell to extracellular matrix Models of Membrane Structures (what led up to Fluid Mosaic Model) Overton Lipid soluble substances enter cell in an easier manner than water-soluble substances Lipophilic = enters easier Cell are coated with a lipid layer (cholesterol and lecithin) Langmuir
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BIO1140 Chapter 7a - Function of Membranes - Cellular...

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