CELL MEMBRANE
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- Membrane structure
- Membranes are composed mainly of lipids and proteins
- Membrane lipids
- Phosphoglycerides are the major
- sphingolipids
- cholesterol
- Phospholipids
- form a bilayer,
- Membrane structure
- hydrophilic head groups interact with water on both the extracellular and intracellular surfaces
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- hydrophobic fatty acyl chains in the central portion of the membrane.
- Peripheral proteins are attached at the periphery of the membrane
- Integral proteins span from one side of the membrane to the other.
- Carbohydrates
- attached to proteins and lipids on the exterior side of the cell membrane
- They extend into the extracellular space.
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- Lipids and proteins
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- can diffuse laterally within the plane of the membrane.
- Therefore, the membrane is termed ‘‘fluid mosaic.’’
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- Membrane function
- Membranes serve as barriers that separate the contents of a cell from the external environment or the contents of individual organelles from the remainder of the cell.
- The proteins in the cell membrane have many functions.
- transport of substances across the membrane.
- enzymes that catalyze biochemical reactions.
- function as receptors that bind external ligands such as hormones or growth factors.
- mediators that aid the ligand–receptor complex in triggering a sequence of events (e.g., G proteins) known as signal transduction;
- second messengers (e.g., cAMP ) that alter metabolism are produced inside the cell.
- cystic fibrosis transmembrane regulator (CFTR)
- results in cystic fibrosis (CF)
- a chloride ion channel found on cell membranes.
- the most common mutation of which is the loss of a phenylalanine residue at position 508, known as the DF508 mutation