Not a Macromolecule, but in the 4 big families


• Diverse group of HYDROPHOBIC molecules • Don’t form true polymers • Often not big enough to be macromolecules • Why hydrophobic?

  • Mostly hydrocarbon regions (H-C)
  • Few polar bonds with O

Most important lipids

  1. Fats
  2. Phospholipids
  3. Steroids

2.1. Fats • Large molecules assembled from smaller molecules by dehydration reaction – Not true polymers • Fat = 1 glycerol + 3 fatty acids – Glycerol = type of alcohol (each carbon has –OH group) – Fatty acid: • Long carbon skeleton, 16-18 C long • C at one end is part of a COOH group (fatty ACID) • Rest of skeleton is hydrocarbon chain • Non-polar C-H bonds are the reason fats are hydrophobic

Fat: 3 fatty acids linked to 1 glycerol by an ester linkage • Also called triacylglycerol or triglyceride • Fatty acids in a fat can be the same, or 2-3 different kinds

• Saturated vs. unsaturated fats – Refers to structure of H-C chains on fatty acids

• Saturated – No double bonds between C atoms – As many H as possible • Most animal fats are saturated • Flexibility from single bonds lets them pack together tightly • Solid at room temperature • Ex: lard, butter

• Unsaturated – One or more double bonds (view image p.84) • A fat made from saturated fatty acids is a saturated fat • Fish and plant fats mostly unsaturated – Built of one or more types of unsaturated fatty acids • Unsaturated fats often liquid at room temperature – Oils • Ex: Olive and cod liver oil – Kinks where double bonds occur prevents them from packing together tightly enough to be solid at room temperature

• Humans need certain unsaturated fatty acids in diet that we can’t produce – Omega-3 fatty acids (for normal growth in kids and to help prevent heart disease in adults) • Found in fatty fish and certain nuts and vegetable oils

• Function of fat → Energy storage • A gram of fat stores more than 2x the energy of a gram of polysaccharide (like starch) • Plants are immobile, can be bulky • Vegetable oil often from seeds, where storage needs to be more compact

• Animals have to carry it with them – needs to be more compact • Stock fat in adipose cells, which swell and shrink with deposit/usage • Fat also cushions vital organs like kidneys and helps insulate – Thick in whales, seals, marine mammals