Chapter 24: Lipid Metabolism

Glycerol

Glycerol

________ is converted to glyceraldehyde 3- phosphate and DHAP, which participate in:

bile acids

The ________ are then available for use in digestion or are excreted via the digestive tract when in excess.

upper end

When partially digested food leaves the stomach, it enters the ________ of the small intestine (the duodenum), where its arrival triggers the release of pancreatic lipases- enzymes for the hydrolysis of lipids.

Ketogenesis

________: The synthesis of ketone bodies from acetyl- CoA.

reaction

The ________ is catalyzed by acyl transferase, and the product is phosphatidic acid.

Lipoproteins

________ are special forms of micelles.

phosphate group

→Next, the ________ is removed from phosphatidic acid by phosphatidic acid phosphatase to produce 1, 2- diacylglycerol.

density lipoproteins

High- ________ (HDLs) (1.063- 1.210 g> cm3) transport cholesterol from dead or dying cells to the liver, where it is converted to bile acids.

dietary lipids

Chylomicrons, which transport ________, carry triacylglycerols through the lymphatic system into the blood and thence to the liver for processing.

Triacylglycerol synthesis

________ proceeds by transfer of first one and then another fatty acid acyl group from coenzyme A to glycerol 3- phosphate.

fatty acid

Once a(n) ________ enters the cytosol of a cell that needs energy, three successive processes occur.

Acyl CoA dehydrogenase

STEP 1: The first B oxidation ________ and its coenzyme FAD remove hydrogen atoms from the carbon atoms a and b to the carbonyl group in the fatty acyl- CoA, forming a carbon- carbon double bond.

Ketone bodies

________: Compounds produced in the liver that can be used as fuel by muscle and brain tissue; for example, 3- hydroxybutyrate, acetoacetate, and acetone.

Lipids

________ are less dense than proteins, the density of lipoproteins depends on the ratio of ________ to protein.

triacylglycerol synthesis

The reactants in ________ are glycerol 3- phosphate and fatty acid acyl groups carried by coenzyme A.

Low density lipoproteins

________ (LDLs) (1.020- 1.062 g> cm3) transport cholesterol from the liver to peripheral tissues, where it is used in cell membranes or for steroid synthesis (and is also available for formation of arterial plaque)

Intermediate density lipoproteins

________ (IDLs) (1.007- 1.019 g> cm3) carry remnants of the VLDLs from peripheral tissues to the liver for use in synthesis.

pathway of dietary triacylglycerols

The ________ from the mouth to their ultimate biochemical fate in the body is not as straightforward as that of carbohydrates.

major bile acid

The ________ is cholic acid, and the structure of its anion closely resembles soaps because it contains both hydrophilic and hydrophobic regions allowing it to act as an emulsifying agent.

bile acids

Among other components, bile contains cholesterol and cholesterol- derived ________, both of which are sterols, and phospholipids.

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Conversion to acetyl-CoA

Activation

The fatty acid is activated by conversion to fatty acyl-CoA

Transport

The fatty acyl-CoA, which cannot cross the mitochondrial membrane by diffusion, is transported by carnitine from the cytosol into the mitochondrial matrix, where energy generation occurs

Oxidation

The fatty acyl-CoA is oxidized by enzymes in the mitochondrial matrix to produce acetyl-CoA, nicotinamide adenine dinucleotide (NADH), and flavin adenine dinucleotide (FADH2 )

The Beta-Oxidation Pathway

The name beta oxidation refers to the oxidation of the carbon atom beta to the thioester linkage in two steps of the pathway

STEP 1

The first B oxidation Acyl-CoA dehydrogenase and its coenzyme FAD remove hydrogen atoms from the carbon atoms a and b to the carbonyl group in the fatty acyl-CoA, forming a carbon-carbon double bond

STEP 2

Hydration Enoyl-CoA hydratase adds a water molecule across the newly created double bond to give an alcohol with the ¬OH group on the b carbon

STEP 3

The second B oxidation The coenzyme NAD+ is the oxidizing agent for conversion of the b¬OH group to a carbonyl group by beta-hydroxyacyl-CoA dehydrogenase

STEP 4

Cleavage to remove an acetyl group An acetyl group is split off by thiolase (acyl-CoA acetyltransferase) and attached to a new coenzyme A molecule, leaving behind an acyl-CoA that is two carbon atoms shorter

Ketone bodies

Compounds produced in the liver that can be used as fuel by muscle and brain tissue; for example, 3-hydroxybutyrate, acetoacetate, and acetone

Ketogenesis

The synthesis of ketone bodies from acetyl-CoA