Lipids 4- Metabolism Flashcards

Flashcards about Lipid Metabolism

Metabolism

Molecules burned up via complex chemical processes to generate energy, also known as catabolism

Cellular respiration

A series of metabolic pathways that convert carbon fuels into CO2 and H2O to generate energy (i.e., ATP)

Epinephrine and glucagon

Hormones that induce lipases

Globular protein albumin

Carbon fuel transported from adipose tissue

FABP

Enzymes used by fatty acids to enter muscle cells since fatty acids are not soluble in aqueous solutions

Lipases

Enzymes: ATGL, HSL, MGL

β-oxidation pathway

Pathway that occurs in the cytoplasm of prokaryotes, but in mitochondria of muscle cells

• observed in eukaryotic adipocytes but considered minor

Activation

Fatty acids must be activated by reacting with coenzyme A to form acyl CoA. This activation takes place on the outer mitochondrial membrane

Acyl CoA synthetase

Enzyme that catalyzes the attachment of a fatty acid to coenzyme A

Oxidation by FAD

1st Reaction in the beta-oxidation pathway that generates trans double bond between carbon-2 and -3;

• enzyme = Acyl CoA dehydrogenase

• Products: Trans-delta2-enoyl CoA and FADH2

Hydration

2nd Reaction in the beta-oxidation pathway that is hydration of trans-Δ2-enoyl CoA by a hydratase;

• enzyme: Enoyl CoA hydratase

• Rxn generates hydroxyl group; single bond between carbon -2 and -3

• products: L-3-hydroxyacyl CoA

Oxidation by NAD+

3rd Reaction in the beta-oxidation pathway is oxidation L-3-hydroxyacyl CoA by a dehydrogenase

• enzyme = L-3-hydroxyacyl CoA dehydrogenase

• reaction converts hydroxyl group to keto group at carbon-3

• Products: 3-ketoacyl CoA and NADH

Thiolysis by coenzyme A

4th Reaction in the beta-oxidation pathway that cleaves 3-ketoacyl CoA by thiol group of a second coenzyme A molecule;

• enzyme: β-ketothiolase

• reaction cleaves 3-ketoacyl CoA into two molecules

• products: acetyl CoA and a fatty acid chain two carbons shorter

Thiolysis

Chemical reaction in which a sulfhydryl (R-SH) functional group cleaves one compound into two.

Enoyl CoA hydratase

Enzyme suppressed by L-3-hydroxyacyl CoA

• steps 1-3 are each controlled by feedback inhibition

PGC-1α

Activates transcription factors, increasing gene expression and regulates the beta oxidation pathway

Cytoplasmic malonyl-CoA, NADH, and acetyl CoA

Suppresses activity of beta-oxidation pathway

Glyceraldehyde 3- phosphate

Molecule directed into glycolysis (generate ATP) or gluconeogenesis (generate glucose), depending on cell’s needs

Mobilization selective

Fatty acids with shorter chains and more unsaturation are metabolized first

FABP

Fatty acids use this to enter muscle cells

Beta-oxidation pathway consists of 4 repeating steps

Each round shortens the FAs hydrocarbon chain by 2 carbons and generates products that can enter cellular respiration

Biochemical activity within the muscle cells

Bringing fatty acids into mitochondria requires activation and ion channels

Ion Channel

Acyl CoA crosses outer mitochondrial membrane (OMM) via

Carnitine in acyl transport

Transport across the inner mitochondrial membrane requires FAs to be linked to an alcohol-carnitine

95% of carnitine is located within the skeletal muscles

• activities at this channel are the rate-limiting step

Beta Oxidation and the Citric Acid cycle

steps 1-3 in beta-oxidation are similar to 6-8 in TCA cycle

example: oxidation by FAD, hydration, and oxidation by NAD+

Both beta oxidation and citric acid cycle occur within

the mitochondrial matrix

• reduced coenzymes donate electrons into the electron-transport chain

What happens to the product Acetyl CoA

Can enter citric acid cycle and generate ATP

What happens to the product NADH and FADH2

Can donate electrons to electron-transport chain

What happens to the shortened FA (acyl group)

continues to be metabolized via beta oxidation

Final thiolysis products for an even chain fatty acid

two acetyl CoA

36 ATP

Combustion of saturated fatty acid hexanoate produces

Odd chain fatty acids

• metabolism also occurs via mucles beta-oxidation pathaway

• final thiolysis products: yield propionyl CoA and acetyl CoA rather than two molecules of acetyl CoA

Propionyl CoA

This three-carbon unit is not an intermediate for cellular respiration, but a carboxylase and a mutase convert it into succinyl CoA, which can enter the citric acid cycle

Aside from this: its a key metabolite for the breakdown of isoleucine, valine, and methionine

Very long chain fatty acids

22 carbons or more are sent to peroxisome first- an organelle containing oxidative enzymes

Unsaturated fatty acids

They require additional enzymes to shift the position and configuration of the carbon-carbon double bonds

Glycerol metabolism

• liberated from tri glycerols during dietary lipid digestion and lipolysis

• sent to the liver, where it is phosphorylated by glycerol kinase

Triacylglycerols in adipose tissue are converted into free fatty acids in response to hormonal signals

such as glucagon and epinephrine, stimulating lipolysis and releasing stored energy for use by the body.

Translocase

Acyl carnitine is shuttled across the inner membrane by a