Lipid Metabolism Flashcards

Flashcards for Lipid Metabolism Lecture Review

Lipid Metabolism

Includes triacylglycerols, fatty acids, and cholesterol.

Konrad Bloch

German scientist awarded the 1964 Nobel Prize for discoveries concerning cholesterol and fatty acid metabolism.

Functions of Lipids

Membrane constituents, hormones, fat-soluble vitamins, thermal insulators, and biological regulators.

Key Questions Addressed in Lipid Metabolism

Fats are mobilized from dietary intake and adipose tissue, lipid molecules are transported in blood, fatty acids are broken down and synthesized, unsaturated fatty acids are oxidized and synthesized, ketone bodies role in metabolism, membrane lipids, sphingolipids, steroids, isoprenoids, and eicosanoids, and their function.

Triacylglycerol

Also known as neutral fats.

Biologically Important Fatty Acids

Saturated and unsaturated fatty acids, differing in melting point and structure.

Triacylglycerols (fats)

A highly reduced and anhydrous energy reserve with 6 times more caloric content than carbohydrates.

Sources of Triacylglycerols

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

Bile Salts

Emulsifiers aiding in triacylglycerol transport through the bloodstream.

Lipoproteins

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

Lipid micelles

Digestive product absorbed and resynthesized into triacylglycerols in intestinal mucosal cells.

Resynthesized Triacylglycerols

Packaged by lipoproteins into chylomicrons for transportation in the lymph system.

Lipoproteins

Soluble aggregates that transport lipids through the blood and lymph.

Major Human Plasma Lipoprotein Classes

Chylomicron, VLDL, IDL, LDL, and HDL

Apoproteins of Human Plasma Lipoproteins

A-I, A-II, B-48, B-100, C-I, C-II, C-III, D, and E.

Chylomicrons

Binding to lipoprotein lipase transports TG from dietary fat to peripheral tissues.

VLDL

Transports TG from the liver to tissues.

Lipoprotein Transport Pathways

Transports dietary fat and cholesterol, involves chylomicrons, VLDL, LDL, and HDL.

Cholesterol Transport and Utilization - Role of LDL

LDL receptor and cholesterol homeostasis, receptor-mediated endocytosis, scavenger receptor from white blood cell, foam cell, atherosclerosis.

Intracellular Cholesterol

Regulates its own level by controlling de novo cholesterol biosynthesis, formation/storage of cholesterol esters, and LDL receptor density.

Statins

Inhibits HMG-CoA reductase.

Release of fat from storage depots

Controlled by hormones (glucagon, epinephrine) via a cyclic AMP-mediated cascade system.

Key Enzymes in Cyclic AMP-Mediated Cascade System

Hormone-sensitive lipase (HSL), Adipose triacylglycerol lipase (ATGL), Monoacylglycerol lipase (MGL).

Franz Knoop

Discovered fatty acid β-oxidation.

Franz Knoop's Early Experiment

Fatty acids are oxidized in a stepwise fashion, with initial attack on carbon 3 (β-carbon). ATP and all intermediates are essential fatty acyl-CoAs.

Fatty Acid Activation and Transport into Mitochondria

Activation, adenylylation, acylation, transfer to carnitine, transport through mitochondrial inner membrane, reconjugation with CoA.

Fatty acid Activation

Through fatty acyl-CoA ligases, adenylylation, acylation

Site for the oxidation of fatty acids

Mitochondria

Transfer to carnitine and transport into mitochondria

Carnitine acyltransferase I and II facilitate the process.

The β-Oxidation Pathway

4 cyclic reactions: Dehydrogenation, Hydration, Dehydrogenation, and Thiolytic cleavage.

Enzymes Needed for Processing Unsaturated Fatty Acids

Enoyl-CoA isomerase and 2,4-dienoyl-CoA reductase.

Control of Fatty Acid Oxidation

Controlled by hormones (glucagon, epinephrine) and malonyl-CoA (inhibitor of carnitine acyltransferase I).

Peroxisomal β-Oxidation of Fatty Acids

Heat generation not energy production, probably for initial stages in oxidizing very long chain fatty acids; electrons are not shuttled into the respiratory chain

α-Oxidation Pathway for Phytanic Acid Oxidation

Defective in Refsum’s disease, leading to accumulation of phytanic acid and severe neurological disorders.