Plasma membrane and Cell transport

• 3 important roles of lipids:

  1. form of storage
  2. plasma membrane
  3. hormone production
• Synthesis of lipids occurs in the Golgi apparatus and smooth endoplasmic reticulum
• T or F: Lipids form better storage than carbohydrates due to compact structure

  True
• All biological membranes are constructed as phospholipid bilayer
• Amphipathic = Non-polar (hydrophobic tails) and polar heads (hydrophilic)
• T or F: WBC is a good model to study plasma membrane because of absence of nucleus

  False
• T or F: Cholesterol in between to aid with fluidity

  True
• Composition of phospholipids

  • 2 Fatty Acids
  • Glycerol
  • Phosphate group
  • Biological molecule
• 5 major phospholipids

  • phosphatidylcholine
  • phosphatidylethanolamine
  • phosphatidylserine
  • phosphatidylinositol
  • sphingomyelin
• Composition of plasma membrane:

  • glycolipids
  • cholesterol
  • phospholipids
• Cholesterol is a major plasma membrane constituent of animal cells
• Cholesterol consists of 4 hydrocarbon rings
• Cholesterol is important for fluidity and integrity of PM
• Composition of cholesterol

  • OH group
  • 4 carbon rings
  • Non-polar (hydrophobic) tail
• OH group (hydroxyl group) makes the head polar and hydrophilic - attracted to the phosphate heads on the periphery of the membrane
• Carbon rings - it's not classed as a fat or an oil, cholesterol is a steroid
• Non-polar (hydrophobic) tail - attracted to hydrophobic tails of phospholipids in the center of the membrane
• Smooth endoplasmic reticulum: site of synthesis of phospholipids
• lipid transfer facilitated by flippases
• newly synthesized lipids added only to cytosolic half of bilayer
• Formation of phospholipids

  A) glycerol-3-phosphate

  B) fatty acyl CoAs

  C) Phosphatidic acid

  D) diacylglycerol

  E) Phosphatidyl choline

  F) phosphate group

  G) CDP

  H) CMP

  
• Glycerol phospholipids are synthesized in the ER membrane from cytosolic precursors
• CoA - Coenzyme A
• Sphingomyelin: primarily found in the outer leaflet
• Sphingomyelin: Contains a serine group instead of glycerol group attached to the choline
• Sphingomyelin: Synthesized in the lumen-side of the Golgi, explains why it is in the outer leaflet of the PM
• glycolipid: Serine associated with 2 FA and carbohydrates
• Inositol incorporated with 2 FA can be considered as a glycolipid
• Remember the sugar structure which is charged and polar. Thus, glycolipids are still amphipathic
• cholesterol: 4 hydrocarbon rings rather than linear hydrocarbon chain. These make cholesterol a steroid
• cholesterol: Increase Fluidity, Decrease Permeability
• cholesterol: in colder temperatures, the Ch maintains the permeability and prevents the membrane from being tightly packed (in nature, during colder temperatures, molecules tend to pack)
• cholesterol: in warmer temperatures, the Ch still makes the PM less permeable. It is also proven that in higher temperature, the PM BP increases
• 4 hydrocarbon rings rather than linear hydrocarbon chain. These make cholesterol a steroid
• OH group: makes the cholesterol polar, it interacts with the polar heads of the phospholipid on the periphery of the membrane. OH is also hydrophilic
• The hydrophobic tail of the Ch interacts with the nonpolar tails of the phospholipids in the center of the membrane
• Interaction between cholesterol and phospholipids provide the fluidity of the plasma membrane
• The plasma membrane appears as two dense lines separated by an intervening space-a morphology frequently referred to as a "railroad track"
• Structures

  A) phosphatidylethanolamine

  B) phosphatidylcholine

  C) phosphatidylinositol

  D) glycolipids

  E) sphingomyelin

  F) phosphatidylserine

  G) cholesterol

  
• Location of phospholipids

  1. Phosphatidylethanolamine - in
  2. Phosphatidylcholine - out
  3. Phosphatidylinositol - in
  4. Glycolipid - out
  5. Sphingomyelin - out
  6. Phosphatidylserine - in