3- Fatty Acid Metabolism Flashcards Preview

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Classifications of lipids

Storage lipids (neutral)
1. Triacylglycerols

Membrane lipids (polar)
1. Phospholipids

2. glycolipids
-galactolipids (sulfolipids)

3. archeabacterial ether lipids



glycerol with 3 fatty acids attached


lipids that do not contain fatty acids


if they contain them then they are "complex lipids"


why are fatty acids physiologically important?

1. building blocks of phospho and glycolipds

2. important amphipathic part of biological membrane

3.post-translational modification: covalent attachment to many proteins target these proteins to membrane locations

4. important source of energy (triglycerides) stored in adipose tissue

5. fatty acid derivatives are hormones and intracellular messengers


what are fatty acids

hydrocarbon derivatives that consist of an alkyl chain (4-36 carbons long) with terminal carboxyl group

- most common ones have EVEN number of carbons

-common in humans: C16 (palmitate), C18 (sterate), C20 but longer ones are typically in nervous system (nervonic acid- sphingolipid) makes myelin


saturated fatty acid

no double bonds

CH3 - (CH2)n - COOH


unsaturated fatty acid

-can have up to 6 double bonds per chain

-they are almost always cis configuration which puts a kink into the alkyl chain

-never directly next to each other but maybe one methylene b/w each double bond group


palmitate / palmitic acid




stearate / stearic acid




nomenclature of fatty acids

chain length: number of double bonds

-start counting carbons at carboxyl then move down and the last carbon is called an omega carbon

-if it says "omega" in the name then count from the other end (not carboxyl)


palmitoleic acid




oleic acid




arachidonic acid

20:4 fatty acid
-key omega 6 fatty acid


Essential fatty acids

polyunsaturated fatty acids (PUFAs) cannot be synthesized in body and must be obtained by dietary sources --> humans lack desaturase enzymes required for their production

-endogenous synthesis may not attain same beneficial high levels as consumption in diet


name the two essential fatty acids

1. Linoleic acid 18:2 (delta 9,12) --> omega-6 fatty acid
-arachidonic acid

2. a-linolenic acid 18:3 (delta9,12,15) --> omega-3 fatty acid



a-linolenic acid 18:3

vegetable oils, nuts, seeds, shellfish, and fish



Linoleic acid 18:2

leafy vegetables, seeds, nuts, grains, vegetable oils, and meats


name 2 key omega 3 and 1 key omega 6 fatty acids?

omega 3
-eicosapentaenoic acid (EPA)
-docosahexaenoic acid (DHA)
-THESE 2 may be in baby formula cause they are important for NS development

omega 6
-arachidonic acid (important precursor for your prostaglandins)


biological functions of of omega 3 and 6 derivatives

eicosanoid synthesis- inflammation

endocannabinoids- mood, behavior, inflammation

imbalance b/w the two is associated with increased risk for CV disease (optimal is omega 6: omega 3 = 1:1 to 4:1)


Non-essential fatty acids

no needed and dont need them from your diet

-monounsaturated FA (lowers LDL)
-saturated FA (raise cholesterol levels)
-trans FA (raise LDL and lower HDL) ---> trans is VERY bad for you


why are trans fatty acids so bad?

-form by partial dehydrogenation of unsaturated FA (done to increase shelf life or stability at high temperature of oils used in cooking- like deep frying)

-trans double bond allows FA to adopt extended/straightened out conformation

-trans can pack for tightly and have higher melting point than cis forms

-consuming trans fats increases risk of CV disease


what determines physical properties of fatty acids

length and degree of unsaturation of hydrocarbon chain


solubility of FA

-poor solubility in water due to non-polar hydrocarbon chain

-the longer the FA chain and the fewer the double bonds, the lower the solubility in water

-more soluble = shorter with double bonds in chain


melting points of FA

-longer acids melt at higher temperatures

-fully saturated FA have waxy consistency due to tighter packing in membrane

-introduction of double bonds (desaturation) results in lower melting points, since kinks in chain dont allow for tight packing
- these weaker interactions increase membrane fluidity (flexibility)- a good thing up to a point


FA synthesis and palmitate

-FA synthesis occurs in liver and cytosol of cells

-process uses carbons from acetyl-CoA into growing FA chain using ATP and reduced NADPH

-plamitic acid (16:0) is the first one to be synthesized then all others are made by its modification


Step 1 of FA synthesis

Formation of malonyl-CoA
-acetyl-CoA provides all carbons for FA and when palmitate is made then
-BUT acetyl-CoA is in the mitochondrial matrix (working with pyruvate dyhydrogenase complex) and FA synthesis happens in the cytosol so you need a way to move acetyl Co-A to the cytosol.


Step 2 of FA synthesis

-moving acetyl-CoA from the inner mitochondrial membrane to the cytosol so you can make malonyl-CoA with it

-Citrate can be freely transported from mitochondrial matrix to cytosol by the TRICARBOXYLATE TRANSPORTER (Citrate transporter)

-it is then converted back to oxaloacetate and acetyl-CoA by ATP-citrate lyase:

Citrate + ATP +*CoASH* ---> oxaloacetate + *Acetyl-CoA* +ADP + Pi


Step 3 of FA synthesis

Requirements: ATP, NADPH, CO2 (HCO3-)

-acetyl-CoA being caboxylated to malonyl-CoA by the enzyme acetyl-CoA carboxylase, which is also essential regulatory enzyme in this pathway


Acetyl-CoA carboxylase

-committed step of FA synthesis (carboxylates acetyl-CoA)

-has 3 functional units, one that has a lysine residue which provides a "swinging arm effect"

-this arm swings "activated CO2" to the acetyl-CoA to form malonyl-CoA


what happens after step 3 of FA synthesis?

-you end up with acetyl-CoA, malonyl-CoA, and NADPH in a repeating 4-step sequence

-the fatty acyl chain is extended by 2C with each passage through the cycle

-Fatty acid synthase complex catalyzes multiple cycles of condensation, reduction, dehydration, then another reduction for a fully saturated acyl group