BCH 4024 Exam 3 Content Chapter 22 (Introduction to Lipid Metabolism)

why are lipids used for energy?

-they contain highly reduced carbons that provide a lot more energy per gram than sugars

-they weigh much less than the equivalent amount of energy in carbohydrates

how is fat stored as energy in cells?

triacylglycerols (TAGs)

what can fatty acid chains of TAGs be converted to in lipid catabolism?

acetyl CoA + propionyl CoA

what can glycerol heads of TAGs be converted to in lipid catabolism?

dihydroxyacetone

what is Step 1 of dietary lipid catabolism?

bile salts from the gallbladder emulsify (breakdown) dietary fats in the small intestine to form micelles

what is Step 2 of dietary lipid catabolism?

pancreatic lipases degrade existing triacylglycerols

what is Step 3 of dietary lipid catabolism?

dietary fatty acids and other breakdown products are taken up by intestinal mucosa and converted into triacylglycerols that the body can use

what is Step 4 of dietary lipid catabolism?

triacylglycerols are packaged into lipoproteins known as chylomicrons to prepare for transportation

what is Step 5 of dietary lipid catabolism?

chylomicrons carry triacylglycerols through the lymphatic system and bloodstream to tissues

what is Step 6 of dietary lipid catabolism?

lipoprotein lipase recognizes and is activated by apoC-II in the capillary to initiate the breakdown of triacylglycerols

what is Step 7 of dietary lipid catabolism?

fatty acids are oxidized for energy or reesterified for storage

function of apolipoproteins in chylomicrons

chylomicron receptor proteins that are recognized by tissue to activate the breakdown of triacylglycerols

what is Step 1 of lipid catabolism by glucagon activation?

activated PKA phosphorylates a hormone-sensitive lipase (HSL) and perilipins in adipocyte

perilipins

proteins attached to CGI-58 that surround fat droplets to shield and protect the droplets

what is Step 2 of lipid catabolism by glucagon activation?

phosphorylated perilipins allow access to fat droplets by releasing CGI-58

what is Step 3 of lipid catabolism by glucagon activation?

CGI-58 activates the enzyme adipocyte triacylglycerol lipase (ATGL)

what is Step 4 of lipid catabolism by glucagon activation?

ATGL breaks triacylglycerol down to diacylglycerol and a fatty acid

what is Step 5 of lipid catabolism by glucagon activation?

the phosphorylated hormone-sensitive lipase (HSL) enters the fat droplet and breaks diacylglycerol down to monoacylglycerol and a fatty acid

what is Step 6 of lipid catabolism by glucagon activation?

monoacylglycerol is broken down to glycerol and a fatty acid

what happens to glycerol produced by lipid catabolism through glucagon activation?

glycerol diffuses through the membrane and travels to target tissue using the bloodstream

what happens to fatty acid chains produced by lipid catabolism through glucagon activation?

they are transported to target tissue using serum albumin

what happens to fatty acid chains once they reach target tissue?

ß-oxidation and formation of acetyl-CoA to produce energy

-what is Step 1 of fatty acid oxidation activation?

-what enzyme is used for this step?

-fatty acid chain is phosphorylated by ATP and grabs CoA-SH to produce a fatty acid CoA and pyrophosphate

-fatty acyl-CoA synthetase

-what is Step 2 of fatty acid oxidation activation?

-what enzyme is used for this step?

-pyrophosphate is broken down into 2 phosphate molecules

-inorganic pyrophosphatase

how is fatty-acyl CoA transported for ß-oxidation in the mitochondrial matrix starting from the cytosol?

it must be converted to carnitine in order to be transported through the intermembrane space

carnitine acyltransferase I (CAT-1)

highly regulated step of ß-oxidation that converts fatty-acyl CoA to fatty-acyl carnitine in the cytosol to prepare for transport through the intermembrane space

carnitine acyltransferase II (CAT-2)

converts fatty-acyl carnitine back to fatty-acyl CoA in the matrix

-what is Step 1 of ß-oxidation?

-what enzyme is involved in this step?

-fatty-acyl CoA undergoes oxidation between the α and ß carbons by reducing FAD to FADH₂, producing a trans-∆²-enoyl-CoA

-acyl-CoA dehydrogenase

-what is Step 2 of ß-oxidation?

-what enzyme is involved in this step?

-the trans-∆²-enoyl-CoA is hydrated, producing a ß-hydroxy acyl-CoA

-enoyl-CoA hydratase

-what is Step 3 of ß-oxidation?

-what enzyme is involved in this step?

-the ß-hydroxy acyl-CoA undergoes oxidation by reducing NAD⁺ to NADH, producing a ß-ketoacyl-CoA

-ß-hydroxy acyl-CoA dehydrogenase

-what is Step 4 of ß-oxidation?

-what enzyme is involved in this step?

-the ß-ketoacyl-CoA is cleaved at the α-ß bond through an attack by CoA-SH, producing acetyl-CoA and a fatty acyl-CoA

-acyl-CoA acetyltransferase

on average, how much ATP is produced from 1 molecule of FADH₂?

1.5

on average, how much ATP is produced from 1 molecule of NADH?

2.5

why is a trans alkene necessary for hydration in ß-oxidation?

enoyl-CoA hydratase only recognizes trans fatty acids

which enzyme catalyzes the conversion of cis unsaturated fatty acids to trans unsaturated fatty acids?

∆³,∆²-enoyl-CoA-isomerase