Lipid Metabolism Flashcards

Flashcards about Lipid Metabolism.

Lipid Metabolism

Study of triacylglycerols, fatty acids, and cholesterol.

Konrad Bloch

German scientist who was awarded the 1964 Nobel Prize in Physiology or Medicine for discoveries concerning cholesterol and fatty acid metabolism.

Functions of Lipids

Functions that include membrane constituents, hormones, fat-soluble vitamins, thermal insulators, and biological regulators.

Triacylglycerol

Neutral fats, composed of glycerol and three fatty acids.

Characteristics of Triacylglycerols

Determined by the types of fatty acids present in the molecule.

Triacyglycerols (fats) as Energy Reserves

Highly reduced and anhydrous, providing 6 times more caloric content by weight than carbohydrate.

Sources of Triacylglycerols

Diet, de novo biosynthesis, and adipocytes (storage).

Gallbladder

Bile salts (emulsifiers).

Triacylglycerols

Transported through the bloodstream via very low-density lipoproteins.

Lipoproteins

Complexing of lipids and proteins to form soluble aggregates for transport through the blood and lymph.

Chylomicrons

Lymph system packaged by lipoproteins for transportation.

Chylomicron, VLDL, IDL, LDL, HDL Desity

Plasma Lipoprotein Classes

Apoprotein A-I

Major protein in HDL; activates LCAT.

Apoprotein A-II

Major protein in HDL.

Apoprotein B-48

Found exclusively in chylomicrons.

Apoprotein B-100

Major protein in LDL.

Apoprotein E

Found in VLDL, LDL, and HDL.

Chylomicrons

Binding of a chylomicron to lipoprotein lipase on the inner surface of a capillary – transport TG from dietary fat to peripheral tissues (heart, muscle and adipose)

VLDL

Transport TG from the liver to tissues. Glycerol and fatty acids catabolized to generate energy or resynthesized TG in adipose tissue.

Transport by serum albumin

From liver & intestine

Cholesterol Transport and Utilization in Animals

LDL receptor and cholesterol homeostasis.

Statins

HMG-CoA reductase inhibitor.

Release of fat from storage depots

Controlled by hormones (glucagon, epinephrine).

Triacylglycerol lipase - hormone-sensitive lipase (HSL)

Cyclic AMP-mediated cascade system.

Franz Knoop

Discovered fatty acid β-oxidation.

Early Experiment Franz Knoop

Fatty acids are oxidized in a stepwise fashion, with initial attack on carbon 3 (-carbon with respect to carboxyl group). ATP was essential and all intermediates are fatty acyl-CoAs.

Fatty Acid Activation and Transport into Mitochondria

Fatty acyl-CoA ligases, adenylylation, acylation Activation and transport Adenylylation ⑭⑪ Acylation of COA-SH ② Transfer to carnitine ③ Transport through mitochondrial inner membrane Reconjugation with CoA

Carnitine acyltransferase I & II

Transfer to carnitine and transport into mitochondria for oxidation.

Oxidation of Fatty Acids Enzymes

Enzymes needed for processing unsaturated and odd numbered chain fatty acids.

Oxidation of Unsaturated Fatty Acids

β-oxidation pathway for polyunsaturated fatty acids Enoyl-CoA isomerase [cis (3,4) → trans (2,3)] and 2,4-dienoyl-CoA reductase (hydrogenation) (cis 4,5 -> cis 3,4)

Malonyl-CoA

Inhibitor of carnitine acyltransferase I → inhibiting fatty acyl-CoA movement into mitochondria by the acylcarnitine shuttle.

Peroxisomal -Oxidation of Fatty Acids

Heat generation not energy production, probably for initial stages in oxidizing very long chain fatty acids The FAD-linked acyl-CoA dehydrogenase transfers electrons not to the respiratory electron transport chain but directly to oxygen. # electrons are not shuttled into the respiratory chain, this pathway is not coupled to energy production, but it does generate heat

Refsum’s disease

Defective α-oxidation pathway - accumulation of phytanic acid - severe congenital neurological disorder.