lecture 11 - lipids and membranes

what are lipids

• nonpolar molecules

• soluble ONLY in nonpolar solvents

• insoluble in water

• composed of fats and oils

• NOT a common class of lipid - glycanoids

examples of lipids

• fatty acids

• triacylglycerols

• phospholipids

• glycolipids / sphingolipids

• steroids

• polyisoprenoids

functions of lipids

• gives structure to cell membrane

• provide energy storage and transport (triacylglycerols)

• aid in digestion

  • bile acids and salts act as detergents in human digestion

• produce hormones (ex: steroids)

• helps absorb nutrients & lipid soluble vitamins

• cell signaling and communication

• body insulation and protection of organs

properties of lipids

• highly hydrophobic or amphipathic

  • NOT highly hydrophilic

• can form bilayers in water

• energy-dense macromolecules

• stored in adipose tissue as triacylglycerols

what are fatty acids

• long hydrocarbon chain that has a carboxylic acid with an aliphatic chain

• can be saturated or unsaturated

saturated fatty acids

• No C=C double bonds

• saturated with hydrogen atoms

• solid at room temperature

• higher melting points

unsaturated fatty acids

• one or more C=C double bonds

• less saturated with hydrogen atoms

• liquids at room temperature

• lower melting points

hydrogenation

turns unsaturated fatty acids (liquids) into saturated fatty acids (solids)

• result - makes lipids more solid at room temperature

• side reaction - produces trans fatty acids

triacylglycerols (TAGs)

• type of lipid made of glycerol + 3 fatty acids

• serves as energy reserves in human adipose tissue

• primary role - energy storage and transport

• found in chylomicrons, which:

  • contain the highest amount of triacylglycerols

  • largest and least dense lipoproteins

  • transport dietary fats

phospholipids and phosphoglycerols

• membrane lipids that make up the cell membrane

• contains - glycerol, 2 fatty acids, phosphate group, & polar or ionic alcohols

• have hydrophilic head and hydrophobic tails

• provides membrane fluidity and structure

• phosphoglycerols - most significant component of mammalian membranes

sphingolipids and sphingomyelin

• sphingolipids - contain a sphingosine backbone instead of glycerol

• sphingomyelin -

  • serves as a common membrane component

  • found in nervous tissue membranes

  • contains 1 esterified fatty acid (differs from phosphoglycerols)

• contributes to membrane stability and cell signaling

cholesterol

• common component of mammalian membranes (along with phospholipids and proteins)

• type of steroid lipid

• adds rigidity and stability to membranes

• waxy, fat-like structure

what do membranes contain

• phospholipids (phosphoglycerols)

• cholesterol

• integral and peripheral proteins

• carbohydrate components of glycoproteins (found on the outer surface only)

what is not a common feature in membranes

complex polysaccharides on the cytosolic inner face

in membranes, membrane fluidity depends on what

membrane fluidity depends on polyunsaturated fatty acid components

types of membrane proteins

integral proteins, peripheral proteins

integral proteins

• embedded in the bilayer (partially or fully)

• difficult to remove

• hydrophobic regions

peripheral proteins

• attached to surface or to other proteins/lipids

• easy to remove

  • can be removed with gentle ionic solutions or limited hydrolytic cleavage

• more hydrophilic character