3- Fatty Acid Metabolism Flashcards Preview

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1

Classifications of lipids

Storage lipids (neutral)
1. Triacylglycerols

Membrane lipids (polar)
1. Phospholipids
-glycerophospholipid
-sphingolipid

2. glycolipids
-sphingolipds
-galactolipids (sulfolipids)

3. archeabacterial ether lipids

2

tricylglyerols

glycerol with 3 fatty acids attached

3

lipids that do not contain fatty acids

cholesterol

if they contain them then they are "complex lipids"

4

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

5

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

6

saturated fatty acid

no double bonds

CH3 - (CH2)n - COOH

7

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

8

palmitate / palmitic acid

C16

16:0

9

stearate / stearic acid

C18

18:0

10

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)

11

palmitoleic acid

C16

16:1

12

oleic acid

C18

18:1

13

arachidonic acid

20:4 fatty acid
-key omega 6 fatty acid

14

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

15

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

16

omega-3

a-linolenic acid 18:3

vegetable oils, nuts, seeds, shellfish, and fish

17

omega-6

Linoleic acid 18:2

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

18

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)

19

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)

20

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

21

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

22

what determines physical properties of fatty acids

length and degree of unsaturation of hydrocarbon chain

23

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

24

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

25

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

26

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.

27

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

28

Step 3 of FA synthesis

Requirements: ATP, NADPH, CO2 (HCO3-)

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

29

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

30

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