17: Lipid and Fatty Acid Catabolism

glycerol

triacylglycerol

triaglycerol

primary form of dietary fat and stored energy in the body, consisting of three fatty acids attached to a glycerol backbone

1. intestinal lipases degrade TGs

2. Fatty acids taken up by intestinal mucosa and converted to TGs

3. Lipoprotein lipase (activated by apoC-II in capillary) converts TGs to fatty acids and glycerols

4. Fatty acids are oxidized as fuel or reesterified for storage

Fat from diet breakdown steps

chylomicrons

mechanism for moving fats around in lymphatic system

serum albumin

a vital protein produced by the liver, essential for maintaining oncotic pressure (keeping fluid from leaking out of blood vessels), transporting hormones, drugs, and fatty acids

1. activate FA via conversion to fatty acyl-CoA

2. transfer FA to mito. matrix

2 steps that must be completed before FA breakdown

carnitine shuttle

used to transport activated FA into mito.

carnitine acyltransferase I, transfer of FA to mito.

committed step of FA breakdown

cartinine acyltransferase 1

critical mitochondrial enzyme located on the outer mitochondrial membrane, catalyzes the rate-limiting step in long-chain fatty acid oxidation by converting Fatty acyl-CoA to fatty acyl cartinine

beta-oxidation

primary metabolic process that breaks down fatty acids into acetyl-CoA units to produce energy

1. Oxidation- FAD —> FADH₂

2. Hydration- add H₂O

3. Oxidation- NAD⁺ —> NADH₂

4. Thiolysis- add CoA-SH

Steps of beta-oxidation

conversion of acetyl-CoA to malonyl-CoA via ACC

committed step of FA synthesis

• acetyl-CoA —> malonyl-CoA

• activated by dephosphorylation

ACC

• export extra acetate units from liver to other tissues to use

• released at high levels in times of starvation

• used as fuel by brain

ketone bodies

HMG-CoA, part of ketogenesis pathway

used in synthesis of sterols and other molecules requiring 5C units

• substrate: 2 acetyl-CoA

• products: acetone and hydroxybutarate

Ketogenesis substrate and products