Transcript Membrane lipids

CH 8: Lipids
Lipids Defined
• A lipid is an organic compound found in living
organisms that is:
– insoluble (or only sparingly soluble) in water
– soluble in non-polar organic solvents.
• Lipids do not have common functional groups
that serves as the basis for defining such
compounds.
Functions of Lipids
1.
2.
3.
4.
5.
Source of energy – 9kcal/gram
Provide thermal insulation and pad organs
Component of all cells – in membranes
Some act as hormones – steroid hormones
Protective coating - waxes
Types of Lipids
1. Energy-storage lipids –triacylglycerols,
triglycerols, “fats”
2. Membrane lipids - phospholipids,
sphingo(glyco)lipids, and cholesterol
3. Emulsification lipids - bile acids
4. Chemical messenger lipids - steroid
hormones and eicosanoids
5. Protective-coating lipids - biological waxes
Fatty Acids (FA)
• Fatty acids are naturally occurring unbranched
monocarboxylic acids
• Biological FA have an even # of carbon atoms:
– Short-chain fatty acids: C4 - C5-6
– Medium chain fatty acids: C6-8 - C10
– Long chain fatty acids: C12 - C26
Types of Fatty Acids
1. Saturated (SFA)
– Fatty acid with only C to C single bonds
2. Unsaturated Fatty Acids
o Monounsaturated (MUFA) - FA with one C to C
double bond present
o Polyunsaturated (PUFA) - FA with 2 or more C to
C double bonds present
Fatty Acids
Mono-unsaturated Fatty Acids
18:1 D 9
w
D
Describing Fatty Acids
• Identify omega & delta “end” of the fatty acid
• State number of carbons: # double bonds
• Give location of double bonds, counting from
the delta “end”
Properties Fatty Acids
• Water solubility decreases as C# increases
– Short chain FA are fairly water soluble
– Medium and long chain FA are water insoluble
• As the number of carbons increases so does the
melting point
• For a given number of carbons, mp increases as
the # of cis double bonds increases
– Trans double bonds do not impact mp significantly
– UC Davis Wiki
Triglyceride = glycerol + 3 fatty acids
aka - triglycerols
TG Formation – 3 ester linkages
Triglyceride
Properties of TG
• The nature of the fatty acids bonded to the
glycerol backbone determines the properties
of the TG
• Fats – solid TG
– Primarily saturated fatty acids
– Primarily animal sources
• Oils – liquid TG
– Many unsaturated fatty acids
– Good sources - plant and fish oils
Sources of FA
• Saturated FA
– Animals fats
– Butter, lard, lamb, beef….
– Coconut “oil”
• MUFA
– Olive oil
– Canola oil
• PUFA
– Vegetable oils, corn oil,
Reactions of TG
1. Hydrolysis
– + 3 H2O  glycerol + 3 FA (or a monoglyceride
and 2 FA)
– Reaction requires heat and acidic conditions OR
digestive enzymes
2. Saponification – 2 step process
– Step one, hydrolyze the TG to 3 FA + glycerol
– Step two, react the FA with 3 NaOH or 3 KOH  3
soaps
3. Hydrogenation reaction
-- add H2 to the double bonds
-- complete hydrogenation converts all double bonds to single
bonds (fully hydrogenated)
--reaction saturates the oil
--partial hydrogenation occurs when some of the double bonds
are hydrogenated
--remaining double bonds are often converted in to
trans form
O
O
H2C O C
H2C O C
O
O
+ 2H2
HC O C
HC O C
O
O
H2C O C
H2C O C
Oil
Solid
4. Oxidation of unsaturated FA –> rancid oil
…CH=CH…. (O) 2 aldehydes (O)  2 carboxylic acids
Essential Fatty Acids
• Fatty acids that must be obtained from dietary sources – are
not synthesized within the body
• Two most important essential fatty acids are:
– Linoleic acid (18:2) - omega 6
– Linolenic acid (18:3) - omega 3
• Both are needed for:
– Proper membrane structure
– Serve as starting materials for the production of
several nutritionally important longer-chain
omega-6 and omega-3 fatty acids
• Current recommended amounts are: total fat
intake in calories:
• 15% - Monounsaturated fat
• 10% - Polyunsaturated
• <10% - Saturated fats
• Studies also indicate that:
– Monounsaturated fats are considered “good fats”
– Saturated fats are considered “bad fats”
– Trans-monounsaturated fats are considered “bad fats”
– Polyunsaturated fats can be both “good fats” and “bad
fats”
• Omega 3 and 6 are important “good fats”
Membrane Lipids
1. Phospholipids
– Glycerophospholipids
– Sphingophospholipids
2. Sphingoglycolipids
3. Cholesterol (steroid)
See page 314
Phospholipids
aka - glycerophospolipid
Sphingophospholipid
• See page 313 and 314
• Sphinogosine backbone with
– Fatty acid bonded to sphingosine by an amide
bond
– Phosphate bonded to an amino alcohol
Relate this structure to that on
page 313
http://themedicalbiochemistrypage.org/sphingolipids.html
http://lipidlibrary.aocs.org/Lipids/introsph/index.htm
Sphingoglycolipids
Cholesterol – found in the
membranes of animal cells
General steroid structure
Steroids – Functions Vary
• Membrane lipids
– Cholesterol – animal cell membranes
• Messenger lipids
– Hormones – testosterone, estrogen, see pages
322/23
• Emulsification lipids
– Bile salts
Messenger Lipids - Eicosanoids
• Eicosanoids are Arachidonic acid (20:4) derivatives:
– Have profound physiological effects at extremely low
concentrations.
– Eicosanoids are hormone-like molecules
– Exert their effects in the tissues where they are synthesized.
– Eicosanoids usually have a very short “life.”
– Physiological effects of eicosanoids:
• Inflammatory response
• Production of pain and fever
• Regulation of blood pressure
• Induction of blood clotting
• Control of reproductive functions, such as induction of labor
• Regulation of the sleep/wake cycle
Eicosanoids
Arachidonic acid (20:4) derivatives