Chapter 11 Lipids
What do we want to understand?
structures of lipid families
physical properties –how these differ from proteins, nucleic acids, and polysaccharides
understand varied roles (leading up to next chapter on membranes)
A. Lipid characteristics
structure: lipids are molecules that possess long chain "fatty acids" (often with significant modifications). What is a fatty acid? In general, it is any organic carboxylic acid (RCO2H) where R can be a long-chain hydrocarbon (12-24 carbons) with or without double bond(s), hydroxyl groups, keto groups, or branching methyl groups (CH3).
physical properties: weak acids, often but not always with a hydrophobic "tail" (the hydrocarbon portion) and hydrophilic "head" (the carboxylic acid or carboxylate group)
B. Biological functions of lipids
energy storage (e.g., triacylglycerols)
insulation
surface barriers (e.g., waxes)
hormones (e.g., steroids)
membrane structure
cell signalling/recognition
C. Lipid families
The following list of fatty acids (on the left) lead to various lipid family members (shown on the right). We will discuss selected members of these family groups.
arachidonic eicosanoids
acid
mevalonic steroids
acid vitamins
linear triacylglycerols
fatty acids glycerophospholipids
sphingolipids
waxes
1. triacylglycerols
role: energy storage
structure:
properties: neutral, hydrophobic
hydrolyzed by lipases
liquid or solid depending on presence
of double bonds
2. eicosanoids
properties: weak acid, some members are quite unstable
fatty acid source: specialized but important family that is derived from one particular fatty acid called arachidonic acid (shown below)
role: smooth muscle contraction, blood vessel constriction, blood clotting
structures: major subfamily is the prostaglandins that show a "hairpin-like" shape; some members have no carbocyclic or heterocyclic rings, some do not
3. glycerophospholipids
role: membrane component, communication
structure:
where Z is a variety of different groups including ethanolamine, choline, serine and inositol
note: cleaved at various points by phospholipases (e.g., snake, bee, wasp venoms) that disrupt membrane structure
4. sphingolipids
role: found in membranes, particularly in nervous system
structure:
where R is a phosphocholine, carbohydrate
properties: amphipathic
5. steroids
fatty acid source: specialized but important family that is derived from mevalonic acid shown below
structures:
