Lecture 2

Lecture 2 - Homeostasis, The Plasma Membrane and Membrane...

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Homeostasis, The Plasma Membrane and Membrane Potential, Action Potential, Synapses and Neuronal Function Chapters 3 and 4
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All communications of the cell with the extracellular environment occur through the plasma membrane Glycoprotein Glycolipid Extracellular fluid Carbohydrate chain Lipid bilayer Cholesterol molecule Phospholipid molecule Channel Intracellular fluid Various membrane proteins Dark line Light space Appearance using an electron microscope Dark line Fig. 3-3, p. 55
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Lipid bilayer ICF (water) ECF (water) Polar heads of phospholipids (hydrophilic) Non-polar tails of Fatty acids (hydrophobic) Polar heads (hydrophilic) Fig. 3-2b, p. 54 The plasma membrane is a lipid bilayer that provides a highly flexible and versatile barrier between the cell and the extra-cellular space. It is turned over, modified and repaired constantly. Cholesterol keeps fatty acids from from packing and crystallizing
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Plasma membrane (trilaminar) provides primary barrier to diffusion. Some substances may cross the membrane (permeable) whereas others cannot (impermeable). Whether or not molecules can pass through membranes is determined by size of the particle and solubility in lipids (so it can pass through the hydrophobic layer). Uncharged or nonpolar molecules such as O2 and CO2, Fatty acids, steroids etc. are highly lipid soluble and pass through the membrane easily. Charged particles such as Na + and K + ions, polar molecules such as glucose and proteins are much less soluble in lipids and cannot pass through the membrane.
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Fig. 3-8, p. 62
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Ways in which molecules pass through membranes Passive diffusion down a concentration gradient. Examples: non-polar molecules such as O2, CO2, fatty acids, steroids. Fig. 3-7, p. 61
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Table 3-1, p. 62
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Ways in which molecules pass through membranes Many molecules cannot penetrate the membrane but can pass through channels composed of proteins. Examples are ions such as Na + , K + , Ca 2+ and Cl - . Passive diffusion is due to concentration gradient and electrochemical gradient. Facilitated diffusion involves a carrier that binds molecules on one side of the membrane, changes confirmation, flips and releases on the other side. Movement down a concentration gradient. E.g. glucose. Carrier can be saturated. Osmosis - movement of water through membranes (channels). passive movement down a concentration gradient.
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Fig. 3-14a, p. 67
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Fig. 3-14b, p. 67
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Fig. 3-14c, p. 67
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Primary active transport by carriers that use energy (ATP) to transport molecules against a concentration gradient. E.g. Na + , K + , amino acids. Carrier can be saturated. Secondary active transport by carriers for specific molecules driven by an ion gradient (usually Na + ) through an ATP dependent pump. E.g. glucose, amino acids and some ions. Endocytosis
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Lecture 2 - Homeostasis, The Plasma Membrane and Membrane...

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