Ch. 11 - Lipid and Amino Acid Metabolism

2% of MCAT Biochemistry content

Where does the mechanical digestion of lipids primarily occur?

In the mouth and stomach

What facilitates chemical digestion of lipids in the small intestine?

Bile, pancreatic lipase, colipase, and cholesterol esterase.

How are digested lipids absorbed?

They may form micelles or be absorbed directly.

How are short-chain fatty acids absorbed?

Across the intestine into the blood.

How are long-chain fatty acids absorbed?

As micelles, then assembled into chylomicrons for release into the lymphatic system.

Which enzyme mobilizes lipids from adipocytes?

Hormone-sensitive lipase (HSL).

What mobilizes lipids from lipoproteins?

Lipoprotein lipase.

What is the role of chylomicrons?

Transport dietary triacylglycerol molecules via the lymphatic system.

What is the function of VLDL?

Transports newly synthesized triacylglycerols from the liver to peripheral tissues in the bloodstream.

What is IDL's role in lipid transport?

Acts as a VLDL remnant transitioning between triacylglycerol and cholesterol transport, picking up cholesteryl esters from HDL.

What is LDL's primary function?

Transports cholesterol for use by tissues.

What is HDL's function in lipid transport?

Involved in the reverse transport of cholesterol.

What regulates interactions between lipoproteins?

Apoproteins.

How is cholesterol obtained?

Through dietary sources or de novo synthesis in the liver.

What is the key enzyme in cholesterol biosynthesis?

HMG-CoA reductase.

What does LCAT catalyze?

Formation of cholesteryl esters for transport with HDL.

What does CETP catalyze?

The transition of IDL to LDL by transferring cholesteryl esters from HDL.

What are fatty acids?

Carboxylic acids with a long chain, which may be saturated (no double bonds) or unsaturated (one or more double bonds).

Where does fatty acid synthesis occur, and what is the precursor?

In the cytoplasm, using acetyl-CoA transported out of the mitochondria.

What are the five steps of fatty acid synthesis?

Activation, bond formation, reduction, dehydration, and a second reduction.

What is the only fatty acid humans can synthesize?

Palmitic acid.

Where does fatty acid oxidation occur, and what transports fatty acids?

In the mitochondria; transport is facilitated by the carnitine shuttle.

What are the steps of β-oxidation?

Oxidation, hydration, oxidation, and cleavage.

What special enzymes are needed for branched and unsaturated fatty acids?

Isomerase and an additional reductase.

When and where are ketone bodies formed?

During prolonged starvation in the liver due to excess acetyl-CoA.

What is the purpose of ketolysis?

Regenerates acetyl-CoA for use as an energy source in peripheral tissues.

How much energy can the brain derive from ketone bodies during starvation?

Up to two-thirds.

Where does protein digestion primarily occur?

In the small intestine.

Under what conditions does cellular protein catabolism occur?

Only during starvation.

What happens to the carbon skeletons of amino acids during catabolism?

They are used for energy via gluconeogenesis or ketone body formation.

Where do amino groups go during protein catabolism?

Into the urea cycle for excretion.

What determines the fate of an amino acid's side chain?

Its chemical properties.