Chapter 11: Lipids

lipid soluability

not solubable in water, highly soluable in organic solvents

5 classes of lipids

• free fatty acids

• triacylglycerols

• phospholipids

• glycolypids

• steroids

5 classes of lipids: fatty acids

• hydrocarbon chain

• carboxyl group (negative charge), methyl group on other end

• saturated (only single bonds) or unsaturated (has c=c)

• energy storage, membrane structure, cell signalling

how does length of fatty acids change

can be long or short but always even number of carbons

monounsaturated fatty acid (MUFA)

one double bond

polyunsaturated (PUFA)

multiple double bonds, bonds seperated by at least 1 methylene (3C distance)

cis double bond

• H on the same side → kinks → don’t pack tightly

• more oily

trans double bond

• H on opposite sides → fatty acids can still pack tight

• more solid

3 types of fatty acid names

• systemic name

• common name

• abbreviated name

3 types of fatty acid names: systemic name

• based on # C (parent carbon - e + oic)

  • C_18: parent hydrocarbon is octodecane → octodecanoic acid

  • “octodec” →18

  • “ane” → single bonds only

gives double bond location from alpha carbon, but often dropped

3 types of fatty acid names: common name

based on what someone decided to name it

3 types of fatty acid names: abbreviated name

#C:# double bonds

• eg 18:2 means 18 C and 2 double bonds

which side does carbon numbering begin from in systemic fatty acid naming

• carboxyl terminus first;

• C2 is alpha

• C3 is beta

• last carbon → omega (ω) carbon atom

how are double bonds represented in systemic fatty acid naming: carboxyl terminus

cis/trans + Δ with superscrip of where the bond appears

• eg cis-Δ⁹ means cis double bond between C9 and 10

how are double bonds represented in systemic fatty acid naming: methyl end

ω + location of first double bond

• omega carbon (methyl) is C1

• eg ω-7 means double bond between C7 and 8 from the omega end

who invented omega naming and why is it useful

• ralph holman

• naming from carboxyl end gets confusing bcs it is reactive (carbon gets ± here) → methyl group is inert

holman’s abbreviated fatty acid naming

#C:#double bondsn-first double bond

• 18:2n-6 means 18 carbons, 2 double bonds, first double bond is C6 counring from the omega end

unsaturated vs saturated fatty acids’ physical properies

• unsaturated have lower melting points → more double bonds, lower melting point

  • cis → kinks → less VDF → lowest melting point

  • trans → pack tight → higher mp than cis

chain length affect on fatty acid melting point

short chain → less VDF → lower metling point

why are cis polyunsaturated fatty acids (PUFA) important

• most fluid type

• essential → we dont produce them, must be eaten

  • omega 3

why can’t we have a high [ ] of fatty acids in our blood

would disrupt pH → stored as triglycerides

5 classes of lipids: triglycerides/triaceylglycerols

• storage unit of fatty acids

• 3 FA ester linked to glycerol

• uncharged

ester bond

COOH + OH → C(=O)-O and water release

why are fats bette for energy storage than carbs

• triacylglycerols are hydrophobic → densly pack together

• carbs are polar → bind water → high water weight

• thus 1g of fat store 6x energy in 1g of glycogen

storage of triglycerides in humans vs plants

• humans → adipose under skin

• plants → seeds

adipose cells

• synthesize and store triglycerides

• contain large lipid droplets

• thermal insulator

how do bases break down triacylglycerols

• sodium or potassium bases

• OH binds glycerol at the ester bonds

• metal binds fatty acid at the carboxyl → forms salts of fatty acid called a soaps

how do soaps get washed away

amphipathic → ionic head interacts with water, hydrophobic tails encapsulate grease and gets washed away in solvent

membrane lipids

• phospholipids

• glycolipids

• cholesterol

5 classes of lipids: phospholipids

• 1 or more fatty acid on a platform + phosphate + alcohol on phosphate

  • platform can be glycerol (phosphoglycerides) or sphingosine (sphingolipids)

• amphipatic

phosphoglyceride structure

phosphatidate + alchohol (polar) group

phosphoglyceride structure: phosphatidate

• glycerol C1 and C2 (sn-1 and sn-2): ester bind to fatty acid COOH

• glycerol C3 (sn-3): phosphate

phosphoglyceride structure: polar alchohol group

• attatches to the phosphate of phosphatidate

• eg choline, serine → phosphatidylcholine or phosphatidylserine

cardiolipin

• double phospholipid → phosphatidate + glycerol + phosphatidate

• 20% of the inner mitochondrial membrane → impermeable, establishing H gradient

sphingolipid

• phosphlipid build on sphingosine (amino alchohol, long unsat hydrocarbon chain) instead of glycerol

• contains ceramides → amino of sphingosine bound to fatty acid

• long and more saturated → form lipid rafts

sphingomyelin

• sphingolipid in membranes → found in myeline sheath of nerves

• amino group links to fatty acid → forms a ceramide

• carboxyl group ester links phosphorylcholine

5 classes of lipids: glycolipids

• lipid + sugar found on on extracellular surface

• derived from sphingosine in animals

  • amino binds fatty acids

  • OH binds sugar(s)

simplest glycolipid

cerebroside → 1 sugar + 1 fatty acid on the sphingolipid

example of complex glycolipid

ganglioside → many sugars attached to sphingolipid

orientation of glycolipids in the membrane

asymmetric → sugar never exposed to cytosol (on extracellular side of cell membrane or on luminal side of organelles)

5 classes of lipids: steroids

• hormones

• steroid nucleus: tetracylic platform → 3 cyclohexanes and 1 cyclopentane

• all steroids are modifications of the steroid nucleus

sterol

family of steroids with an alchohol functional group

cholesterol

• most common steroid

• -ol denotes alcohol → type of sterol

• maintains membrane fluidity

• precursor of steroid hormones

membrane anchors

hydrophobic tail attached to protein → helps anchor hydrophillic protein to hydrophobic membrane interior