BIOC2000 Lecture Notes - Lecture 19: Olive Oil, Lipid Bilayer, Carboxylic Acid
Lecture 19&20: Lipids
LECTURE 19
• Biological lipids are chemically and functionally diverse.
• Their common and defining feature is their insolubility in water.
• Fats and oils-store energy
• Phospholipids and sterols – major structural elements of membranes; e.g.
membrane bilayer is made from phospholipids
•Other lipids are enzyme cofactors, electron carriers, pigments,
hydrophobic anchors for membrane-associated proteins, chaperones,
emulsifying agents, hormones, and intracellular messengers.
Will focus on highlighted section
8 General Categories
- Fatty acids
- Glycerolipids
- Glycerophospholipids
- Sphingolipids
- Sterol lipids
- Prenol lipids
- Saccharolipids
- Polyketide
- important in eukaryotic biology, bacteria and archaea
Fatty acids as energy storage units
The fats and oils used for storage of energy in biology are derivatives of
fatty acids, which comprise a carboxyl group and a linear hydrocarbon
chain.
Fatty acids are long hydrocarbon chains, and the carbons are highly
reduced.
There are:
(a) saturated fatty acids – ‘saturated’ with H+ , cannot add any more H+
(b) unsaturated fatty acids – have at least 1 double bond, could be reduced
by additional of 2 (or more) H+
Similarities/differences of fatty acids (FA) with carbohydrate structures:
- partially oxidized C (on COOH) in FA, in carbohydrates it was a carbonyl
- linear chain of C in FA, in carbohydrates it was mainly 6C’s long, slightly
shorter
- H+ attached in FA, in carbohydrates it was 1 H+ and 1 OH group attached
; hydrocarbon (completely protonated C chain) vs. a‘ a hydrate of C’
(carbohydrate)
This shows perhaps sugars are partially oxidized lipids, but not completely
oxidized - there’s a lot of energy that is accessible by further oxidation
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Perhaps that’s an interesting medium of energy storage for organism
Fats are useful for long-term stable energy storage because they are
almost completely reduced – whole lot of energy packed in these
molecules; however they are relatively inaccessible
But if you partially oxidise them, they become water soluble (like
carbohydrates) but they are a little bulkier and you cannot store as much
energy in a sugar as you can in a fat, as they are less compact structures
Oleic acid is present in olive oil.
The 1st number 18 presents the # of C’s in the chain
The 2nd number (after the ‘:’) represents the # of double bonds in the chain
Δ9 – double bond is present after the 9th C in the chain
Know how to draw a fatty acid (shown above, middle)
1. Draw C1 at top with COOH/or carboxyl group (COO-) depending on pH
of local environment
2. Draw C chain below zigzagged (2 H+ per C is assumed)
- In a carbohydrate, C’s are chiral i.e. there are 4 different substituents on
each C atom: OH , H+ (on opp. sides), top part of sugar and bottom part.
(shown above, far right). Whether OH is on one side or the other, changes
its stereochemistry and hence makes a different structure
- In lipids, all the C’s are not chiral so Fischer projection drawings are not
required
Single bonds are rotationally flexible, and this is shown with zigzag
General structures of fatty acids are conserved
Monounsaturated fatty acids generally have their double bond between C-
9 and C-10 (Δ9).
Polyunsaturates generally have their other double bonds at
Δ12 and Δ15
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The most common fatty acids have
1) even numbers of carbons,
2) an unbranched C chain,
3) 12-24 carbons
There are two acceptable ways of naming and numbering fatty acids. The
“chemistry” way is the one we mostly use in this course and in Lehninger
Standard chemistry nomenclature assigns the number 1 to the carboxyl
carbon and α to the carbon next to it. The position of any double bonds
are given as Δ with a superscript that indicates the lower numbered
carbon involved in the double bond.
‘omega-3 fatty acids’ have a double bond from the 3rd C from the end
C(“C1”ω) of the molecule (Physiology nomenclature)
- this is a relatively common naming system but not used in BIOC2000
What’s the point of the saturation and unsaturation for
biology?
A double bond forces a kink in the structure – this changes how these
molecules interact and overall biophysical properties of these lipids
Saturated fatty acids:
- completely flexible and ‘wobbly like cooked spaghetti in a bowl’
- form compact structures
- strong van der Waal’s interactions
- a lot of heat and energy would be required to break those interactions so
at RT, they are SOLID
- Increasing T (e.g. heating up butter), eventually fats will melt because T
will be hot enough to break these VDW interactions
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find more resources at oneclass.com
Document Summary
Important in eukaryotic biology, bacteria and archaea. The fats and oils used for storage of energy in biology are derivatives of fatty acids, which comprise a carboxyl group and a linear hydrocarbon chain. Fatty acids are long hydrocarbon chains, and the carbons are highly reduced. There are: (a) saturated fatty acids saturated" with h+ , cannot add any more h+ (b) unsaturated fatty acids have at least 1 double bond, could be reduced by additional of 2 (or more) h+ Similarities/differences of fatty acids (fa) with carbohydrate structures: Partially oxidized c (on cooh) in fa, in carbohydrates it was a carbonyl. Linear chain of c in fa, in carbohydrates it was mainly 6c"s long, slightly shorter. H+ attached in fa, in carbohydrates it was 1 h+ and 1 oh group attached. ; hydrocarbon (completely protonated c chain) vs. a a hydrate of c" (carbohydrate)
