Biochemistry of Lipoprotein Lipase

Questions and Answers

What primary function does lipoprotein lipase serve in the metabolism of chylomicrons (CM)?

Synthesizes new lipoproteins from remnants

Converts chylomicrons directly into LDLs

Hydrolyzes TAG to release fatty acids and glycerol (correct)

Increases the size of chylomicrons

Where is lipoprotein lipase predominantly found in the human body?

Liver

Adipose tissue (correct)

Kidneys

Pancreas

What happens to the capping protein apolipoproteins after TAG degradation in chylomicrons?

They are transferred to VLDLs

They return to high-density lipoproteins (HDLs) (correct)

They remain attached to the remnants

They are completely destroyed

What role do hepatocyte lipoprotein receptors play in chylomicron metabolism?

They facilitate the removal of remnants via endocytosis Signup and view all the answers

Which statement about lipoprotein lipase is true?

It is absent in adult liver tissue Signup and view all the answers

What is the primary composition released from chylomicron remnants after hydrolysis by the liver?

Amino acids and free cholesterol Signup and view all the answers

Which enzyme is activated by apo C-II in circulating lipoprotein particles?

Lipoprotein lipase Signup and view all the answers

What ultimately happens to the remnants of chylomicrons after interaction with hepatocytes?

They are taken up into lysosomes for hydrolysis Signup and view all the answers

Which apolipoproteins are specifically recognized by liver lipoprotein receptors for the uptake of chylomicron remnants?

Apo B-48 and E Signup and view all the answers

What characterizes the condition of complete absence of β-lipoproteins?

Complete absence of VLDLs Signup and view all the answers

How does dietary intake of trans fatty acids affect lipoprotein levels?

Increases levels of lp(a) Signup and view all the answers

What is the primary impact of estrogen on lipoprotein metabolism?

Decreases levels of LDL and lp(a) Signup and view all the answers

What is a significant feature of HDL deficiency known as Tangier Disease?

Presence of ABCA1 deficiency Signup and view all the answers

What therapy is effective in treating the neurological symptoms associated with disorders of lipoprotein metabolism?

There is no effective treatment Signup and view all the answers

What condition is characterized by abnormally high levels of one or more plasma lipoproteins?

Hyperlipidemia Signup and view all the answers

What is the primary action of hepatic lipase?

Assists with HDL metabolism Signup and view all the answers

Which factor is crucial for the regulation of lipoprotein lipase activity?

Insulin levels Signup and view all the answers

What characteristic differentiates the adipose enzyme of lipoprotein lipase from the heart muscle lipoprotein lipase?

Higher Km value Signup and view all the answers

What are VLDLs primarily composed of?

Triacylglycerols (TAG) Signup and view all the answers

Where is hepatic lipase located?

Surface of hepatic endothelial cells Signup and view all the answers

What process leads to the transition from VLDL to LDL in the plasma?

Action of lipoprotein lipase Signup and view all the answers

What is the consequence of elevated plasma lipoprotein concentrations on adipose lipoprotein lipase?

Enhanced fatty acid removal for TAG storage Signup and view all the answers

What is the main function of lipoprotein lipase in the circulation?

Degrade TAG in lipoproteins Signup and view all the answers

How does the Km of heart muscle lipoprotein lipase compare to that of adipose lipoprotein lipase?

It is lower, allowing for rapid uptake of fatty acids Signup and view all the answers

What is the initial product of VLDL degradation in the plasma?

LDL Signup and view all the answers

What is a primary consequence of uncontrolled diabetes mellitus on hepatic function?

Increased synthesis of VLDL Signup and view all the answers

Which apolipoprotein is crucial for the activation of lipoprotein lipase?

Apo C-II Signup and view all the answers

What characterizes familial type III hyperlipoproteinemia?

Deficiency in clearance of chylomicron remnants Signup and view all the answers

What triggers down-regulation of lipoprotein receptors in cells?

Large amounts of circulating plasma lipoprotein Signup and view all the answers

Which isoform of apo E is suggested to bind poorly to receptors?

Apo E2 Signup and view all the answers

What is the primary function of lysosomal enzymes in relation to lipoprotein remnants?

To degrade lipoprotein remnants and release essential nutrients Signup and view all the answers

What is the primary function of apolipoprotein B-100 in VLDL particles?

Acts as a ligand for receptor-mediated endocytosis Signup and view all the answers

What happens during up-regulation of lipoprotein receptors in cells?

Cells increase the number of cell-surface receptors in response to low cholesterol Signup and view all the answers

Which component is NOT released from lipoprotein remnants during lysosomal degradation?

Triglycerides Signup and view all the answers

Excessive chronic ethanol ingestion leads primarily to which hepatic condition?

Hepatic steatosis Signup and view all the answers

What role does apo E play in the clearance of lipoproteins?

It binds to VLDL for degradation in the liver. Signup and view all the answers

How do cell needs affect the number of available receptors for lipoproteins?

More receptors are present when nutrient demand is high Signup and view all the answers

What physiological condition leads to the down-regulation of lipoprotein receptors?

Abundance of circulating plasma lipoprotein Signup and view all the answers

Which of the following conditions is NOT associated with hepatic TAG synthesis imbalance?

Hyperthyroidism Signup and view all the answers

Why is apo E potentially involved in familial dysbetalipoproteinemia?

Because of its homozygous effect on metabolism. Signup and view all the answers

Which process allows for the reuse of lipoprotein components by the cell?

Degradation by lysosomal enzymes Signup and view all the answers

The release of nascent VLDL particles occurs primarily through which mechanism?

Lipid droplet mobilization Signup and view all the answers

What is the consequence of prolonged starvation of cholesterol in cells?

Increased number of lipoprotein receptors on cell surfaces Signup and view all the answers

Which of the following statements about lipoprotein receptor availability is true?

Cell needs directly influence receptor numbers Signup and view all the answers

Which of the following does NOT represent a component released during the degradation of lipoprotein remnants?

Nucleotides Signup and view all the answers

Study Notes

Chylomicron and Lipoprotein Metabolism

Chylomicrons (CM) contain triglycerides (TAG) in their core, which are degraded by lipoprotein lipase, leading to smaller size and increased density of particles.
Apolipoproteins from CMs return to high-density lipoprotein (HDL) particles after delipidation, leaving a "remnant" particle.
CM remnants are removed from circulation primarily by the liver.

Lipoprotein Lipase Enzyme

Lipoprotein lipase is an extracellular enzyme anchored to capillary walls by heparan sulfate, notably in adipose tissue, cardiac, and skeletal muscle.
It is activated by apo C-II and hydrolyzes TAG in lipoprotein particles into fatty acids and glycerol; absent in adult liver.
Hepatic lipase is located on hepatic endothelial cells and aids HDL metabolism but does not significantly affect chylomicrons or VLDL TAG.

Regulation of Lipoprotein Lipase Activity

Insulin promotes lipoprotein lipase synthesis, signaling a fed state.
Adipose tissue lipoprotein lipase has a large Km, allowing for fatty acid removal during elevated lipoprotein concentrations.
Heart muscle lipoprotein lipase has a smaller Km for more efficient uptake of fatty acids.

VLDL Metabolism

Very Low-Density Lipoproteins (VLDL) are synthesized in the liver, primarily containing TAG, and transport TAG to peripheral tissues.
VLDL undergo degradation in plasma, transitioning to low-density lipoproteins (LDL) while some can also be taken up by cells via receptor-mediated endocytosis using apo E as a ligand.

Fatty liver (hepatic steatosis) results from an imbalance in TAG synthesis and VLDL secretion, often associated with conditions like hepatitis, obesity, uncontrolled diabetes, and chronic ethanol ingestion.

Apolipoproteins and Receptor Dynamics

Apo E exists in three isoforms and is essential for clearance of lipid particles; deficits in apo E2 can lead to familial type III hyperlipoproteinemia.
Receptor levels for lipoproteins adjust based on cellular needs, with down-regulation occurring in response to high plasma lipoprotein levels and up-regulation during cholesterol starvation.

Disorders of Lipoprotein Metabolism

Hyperlipidemias feature abnormally high levels of one or more plasma lipoproteins, leading to various metabolic disorders.
Tangier Disease is a rare condition characterized by HDL deficiency due to ABCA1 mutations, resulting in low plasma cholesterol and normal or increased TAG levels.

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Description

Explore the complex interactions of lipoprotein lipase and its role in lipid degradation. This quiz covers key concepts of lipid metabolism, including delipidation and changes in size and density of lipoproteins.