cell membrane - The Cell Membrane Contains lipids proteins...

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The Cell Membrane: Contains lipids, proteins, and carbohydrates Membrane Lipids: -Phospholipids are a major component of cell membranes. -The phosphate group serves as a link between a diglyceride (a glycerol molecule bonded to two fatty acid “tails”) and a nonlipid head. -The phospholipids lie in two layers, the hydrophilic heads on the outside and the hydrophobic tails on the inside. This is why the cell membrane is called a phospholipids bilayer. -the tails don’t associate with water or charged molecules so it acts as a selective physical barrier. Membrane Proteins: Membrane proteins may function as receptors, channels, carriers, enzymes, anchors, or identifiers. Receptor proteins- Sensitive to specific extracellular materials that bind them and trigger a change in a cell’s activity. Channel proteins- Central pore, or channel, permits water, ions, and other solutes to bypass lipid portion of cell membrane. Carrier proteins- Bind and transport solutes across the cell membrane. This process may or may not involve energy. Enzymes- Catalyze reactions in the extracellular fluid or within a cell. Anchoring proteins- Attach the cell membrane to other structures and stabilize its position Identifier proteins- Identify a cell as self or nonself, normal, or abnormal, to the immune system. Membrane Carbohydrates- Carbohydrates form complex molecules with proteins and lipids on the outer surface of the membrane. -the carbohydrate portion of molecules, such as glycoprotein’s and glycolipids, fucking as cell lubricants and adhesives, act as receptors for extracellular compounds, and form part of a recognition system that keeps the immune system from attacking the bodies own cells and tissues. Membrane Transport: -Permeability of a cell determines what substances enter and leave the cytoplasm. -Impermeable- when nothing can cross a membrane -Freely permeable- substance can cross without difficulty
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-Selectively permeable- free passage of some materials and restricting the passage of others *Movement can be passive or active -Passive processes move ions or molecules across the cell membrane without any energy expenditure by the cell
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