lipids

• lipids

  • Naturally occurring fats and oils are triesters formed between glycerol and fatty acids
  • In natural fats and oils, the double bonds are usually cis rather than trans.

  A) cholesterol

  B) wax

  
• triglycerides/triacylglycerols

  • 3 fatty acids + glycerol = triglyceride + 3H2O
  • animal fats & plant oils are the most common lipids
  • animal fat = solid, plant oil = liquid, but similar structures

  
• fatty acids

  • are long unbranched chain with carboxylic acid group
  • have even number of carbons with straight chain

  
• melting points of fatty acids

  • saturated have higher MP than unsaturated due to difference in 3D shape of the chains
  • double bonds allow the formation of cis/trans isomers (geometric) and adds kinks to the chain, thus poorer packing and less intermolecular forces
• fatty acids (continued)

  • The C=C in vegetable oils can be hydrogenated to yield saturated fats, reducing oxidative rancidity
  • trans - act like saturated fatty acids (linear chain, tight packing, solids)
  • cis - are the ones that form kinks due to H's being on the same side of C=C, causing bend

  A) cis

  B) trans

  C) saturated

  
• soaps and detergents

  • saponification: boiling animal fat (triglyceride) + NaOH = natural soap + glycerol
  • this is an ester hydrolysis reaction
  • the ionic group is extremely water soluble

  A) acid
• what happens when soap is mixed with water-insolubles?

  1. soap molecules form micelles spontaneously
  2. micelles have hydrophilic ionic ends and long hydrophobic chains
  3. when mixed with water-insoluble grease, the nonpolar parts of the micelle "dissolves" the nonpolar molecules
  4. these then get washed away in the polar water

  A) micelle

  B) hydrophilic

  C) hydrophobic

  
• precipitation of soaps in hardwater

  • hard water: water with high mineral content (eg. Ca, Mg, Fe)
  • The metal ions replace Na+ or K+ in soap molecule, forming an insoluble salt

  
• artificial soaps/detergents requirements:

  1. hydrocarbon tail of 12 - 20 C's
  2. a polar head group that does not form insoluble salts with Ca2+, Mg2+, or Fe3+ ions.
  3. contains alkylbenzenesulfonates (LAS) - have really polar SO3- group (doesn't form insoluble salts)

  
• Phospholipids

  • 2nd most naturally occuring lipid, found in 40-50% of animal and plant membranes
  • Glycerol+2 Fatty Acids+Phosphate Group→Phospholipid+Water
  • derived from phosphatidic acid

  A) phosphatidic

  B) head

  C) glycerol

  
• phospholipids (continued)

  • The bilayer is highly ordered and stable, but flexible.
  • When shaken vigorously with water, they form liposomes — small spherical vesicles with a lipid bilayer surrounding an aqueous center.
  • function: useful as carriers for drug delivery because they can fuse with cell membranes and empty their contents into the cell

  A) liposome

  B) micelle

  
• fluid mosiac model

  • describes the structure of the cell membrane as a dynamic, flexible structure made up of different components.
  • fluid: the proteins of membranes “float” in the bilayer and move freely along the membrane.
  • Mosaic: reflects a diverse range of molecules making up membrane, forming mosaic pattern. (eg. phospholipids, proteins, glycolipids, cholesterol)

  
• steroids

  • group of plant and animal lipids that have a tetracyclic ring structure
  • Steroid systems are nearly flat and quite rigid

  type of steroid - cholesterol

  • regulates fluidity of cell membrane.
  • in low temps, it prevents fatty acids from packing too close
  • in high temp, prevents excessive fluidity

  A) cholesterol

  B) steroid

  
• Lipid-derived hormones

  • androgen: male sex hormone
  • anabolic steroids: promotes tissue and muscle growth and development
  • estrogen: female sex hormone