Plasma Membranes

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Structure

  • composed of lipids, proteins and carbohydrates

FLUID MOSAIC MODEL

  • Controls entry and exit: proteins that allow water-soluble substances in and out.
  • Forms a barrier against water-soluble substances:phospholipid molecules have a hydrophilic head; hydrophobic tail→ arrange themselves in a bilayer.
  • Allows cell communication: receptor proteins detect chemicals released from other cells→ response is carried out.
  • Allows cell recognition: gylcoproteins and glycolipids→ WBC recognises cell as your own→ no immune response carried out on own cells.
  • Is fluid: cholesterol fits in between bilayer- reduces fluidity- more rigid; prevents it from breaking up.

(http://upload.wikimedia.org/wikipedia/commons/thumb/d/da/Cell_membrane_detailed_diagram_en.svg/2000px-Cell_membrane_detailed_diagram_en.svg.png)

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Lipids in Membranes

TRIGLYCERIDE

  • one molecule of gylcerol; 3 fatty acids
  • fatty acids have long tails made of hydrocarbons (hydrophobic)

FATTY ACIDS

  • Saturated: single bonds between carbon atoms
  • Unsaturated: double bonds between carbons: the more unsaturated the more fluid the membrane is.

TRIGLYCERIDE FORMATION

  • formed by condensation reaction
  • ester bond formed
  • H2O released
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Phospholipids

One phosphate group- hydrophilic

Two Fatty acids

One glycerol molecule

(http://upload.wikimedia.org/wikipedia/commons/2/29/Phospholipid_Chemicalmakeup.png)

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The test

  • shake sample with ethanol: dissolve the lipids.
  • pour in water- lipids can't dissolve in water
  • creamy emulsion appears is lipids are present.

(http://www.scielo.org.ar/img/revistas/laar/v41n2/a02f03.png)

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