Biosynthesis of Membrane Lipids and Steroids

300 flashcards covering the biosynthesis of membrane lipids and steroids, focusing on key concepts, definitions, and processes related to lipid metabolism.

What are the main targets of drug therapy in lipid biosynthesis?

Enzymes involved in the biosynthetic pathways of lipids.

What do statins inhibit in cholesterol biosynthesis?

The committed step of cholesterol biosynthesis.

What relationship should you identify between triacylglycerol synthesis and phospholipid synthesis?

Both processes are interconnected, sharing common intermediates.

What is the first stage of cholesterol biosynthesis?

The conversion of HMG-CoA to mevalonate, catalyzed by HMG-CoA reductase.

Where does triacylglycerol synthesis primarily occur?

In the liver.

What is phosphatidate?

A common intermediate in the synthesis of phospholipids and triacylglycerols.

Which enzyme hydrolyzes phosphatidate to produce diacylglycerol?

Phosphatidic acid phosphatase.

What type of lipids do sphingolipids contain?

A sphingosine backbone.

What is ceramide?

A lipid consisting of a fatty acid chain attached to the amino group of a sphingosine.

What are gangliosides?

The most complex sphingolipids that contain oligosaccharide chains.

What inherited disorder affects ganglioside metabolism?

Tay-Sachs Disease.

What enzyme is deficient in Tay-Sachs disease?

β-N-acetylhexosaminidase.

What are the three stages of cholesterol synthesis?

Stage 1: synthesis begins in the cytoplasm; Stages 2 and 3 occur in the endoplasmic reticulum.

What is the committed step in cholesterol biosynthesis?

The reduction of HMG-CoA to mevalonate.

What are the substrates and products of the reaction catalyzed by HMG-CoA reductase?

3-Hydroxy-3-methylglutaryl CoA is converted into mevalonate.

How do statins affect cholesterol levels?

By blocking HMG-CoA reductase, leading to lower cholesterol levels.

What happens during the conversion of lanosterol to cholesterol?

It requires 19 steps and 9 different enzymes.

What is the role of SREBP in cholesterol regulation?

It regulates the transcription of genes encoding proteins involved in lipid synthesis.

What is the effect of high cholesterol levels on HMG-CoA reductase?

It decreases the activity of HMG-CoA reductase.

How are lipids transported in the body?

Via lipoproteins.

What structure do apolipoproteins provide to lipoproteins?

Solubility of lipids and stability.

What happens to excess cholesterol from the liver?

It is either used or excreted.

What is the composition of chylomicrons?

About 90% triacylglycerol content.

What are the two important types of apolipoproteins in VLDL?

Apo B-100 and Apo E.

What type of receptor is crucial for LDL uptake in cells?

LDL receptor.

What is reverse cholesterol transport?

The process by which HDL removes cholesterol from cells and returns it to the liver for excretion.

What genetic condition is associated with high levels of LDL and atherosclerosis?

Familial hypercholesterolemia.

What are bile salts synthesized from?

Cholesterol.

What is the function of bile salts in the intestine?

To solubilize dietary lipids.

Which major classes of steroid hormones derive from cholesterol?

Progesterone, glucocorticoids, mineralocorticoids, androgens, and estrogens.

What is the precursor for glucocorticoids such as cortisol?

Cholesterol.

What role does aldosterone play in the body?

It regulates sodium and potassium balance.

What is the significance of estrogen in female physiology?

It is required for the development of female secondary sex characteristics.

What structural feature distinguishes cholesterol from other lipids?

Its polycyclic structure.

What is the function of HDL in lipid metabolism?

To transport cholesterol from peripheral tissues back to the liver.

What is the typical composition of low-density lipoprotein (LDL)?

A core of cholesterol molecules esterified to fatty acids.

Why is HDL referred to as protective against atherosclerosis?

It facilitates the removal of excess cholesterol from tissues.

How does genetic disease affect lipid metabolism?

It may disrupt normal digestive or synthetic pathways, leading to accumulation of harmful substances.

What is the primary site of cholesterol synthesis in the body?

The liver.

How many carbon atoms does cholesterol have?

27 carbon atoms.

What is the fate of cholesterol that is not used by cells?

It is excreted via bile or converted to bile salts.

How does the body regulate the activity of HMG-CoA reductase?

By feedback inhibition from cholesterol levels.

What enzyme converts mevalonate into other intermediates in cholesterol biosynthesis?

Various enzymes through multiple reaction steps.

What happens to HDL levels during atherosclerosis?

They typically decrease, leading to reduced cholesterol removal.

How are bile salts effective detergents?

Because they possess both polar and nonpolar regions.

What is the implication of increased lipoprotein density?

Higher density lipoproteins typically contain more protein and less triglyceride.

What component is essential for the emulsification of dietary fats?

Bile salts.

How do liver cells uptake excess lipoproteins?

Through receptor-mediated endocytosis.

How does the structure of lipid rafts relate to lipoproteins?

They stabilize the membrane microdomains necessary for certain signaling pathways.

What impact does dietary intake of cholesterol have on serum cholesterol levels?

It can directly influence the level of LDL cholesterol in the plasma.

What molecules form the hydrophobic core of lipoproteins?

Triglycerides and cholesterol esters.

What are the consequences of high LDL levels in the blood?

Increased risk of cardiovascular diseases and atherosclerosis.

What role do lipases play in lipid metabolism?

They hydrolyze triglycerides in lipoproteins for energy release.

Define the term 'apolipoprotein'.

Proteins that bind lipids to form lipoproteins.

What action occurs when the liver synthesizes very-low-density lipoprotein (VLDL)?

It exports triglycerides to peripheral tissues.

Describe the composition of high-density lipoprotein (HDL).

Composed of phospholipids, cholesteryl esters, and proteins.

What genetic disorders can lead to dysfunction in lipid metabolism?

Conditions like Tay-Sachs and familial hypercholesterolemia.

What is the general effect of statins on lipid levels?

They lower the levels of LDL cholesterol in the bloodstream.

What is the clinical importance of knowing cholesterol synthesis pathways?

It helps in the development of therapies for cardiovascular diseases.

What happens during the enzymatic conversion of cholesterol to bile acids?

It involves hydroxylation and side chain modifications.

Identify the relationship between HDL and cardiovascular health.

Higher HDL levels are correlated with lower cardiovascular risk.

What role does the endoplasmic reticulum play in cholesterol metabolism?

It is the site where several steps of cholesterol synthesis occur.

What process facilitates the uptake of LDL by peripheral tissues?

Receptor-mediated endocytosis.

How does oxidized LDL contribute to atherosclerosis?

It gets taken up by macrophages, forming foam cells that lead to plaque formation.

What type of lipoproteins are primarily responsible for transporting triglycerides?

Chylomicrons and VLDL.

What is the significance of ceramide in sphingolipid synthesis?

It serves as the initial product for synthesizing more complex sphingolipids.

What are the major consequences of high levels of triglycerides in the bloodstream?

Increased risk of pancreatitis and cardiovascular diseases.

How do environmental factors influence cholesterol levels in the body?

Diet, physical activity, and weight management can alter cholesterol metabolism.

What is the physiological role of glucocorticoids like cortisol?

They manage stress responses and influence glucose metabolism.

Explain the term 'reverse transport' in the context of cholesterol metabolism.

It refers to the transfer of cholesterol from peripheral tissues back to the liver.

How do genetic variants impact lipid metabolism?

They can affect enzyme function, receptor activity, and lipid processing.

What enzyme is critical for the mobilization of stored lipids?

Hormone-sensitive lipase.

How does insulin affect lipid metabolism after meals?

Insulin promotes lipid storage and inhibits lipolysis.

What risk is associated with high levels of total cholesterol?

Increased risk of cardiovascular disease.

What kind of lipoprotein is more associated with negative cardiovascular outcomes?

Low-density lipoprotein (LDL).

How does the dynamic nature of lipoproteins facilitate lipid metabolism?

Their composition and structure allow for effective lipid transport and exchange.

What is the clinical significance of monitoring lipid profiles?

It helps assess cardiovascular risk and guide dietary and pharmacological interventions.

How are cholesterol esterified in lipoproteins?

Through the action of lecithin-cholesterol acyltransferase (LCAT).

What is the impact of dietary fats on long-term cholesterol synthesis in the liver?

Dietary fats can modulate hepatic cholesterol synthesis based on the types consumed.

What is the role of phospholipids in lipoproteins?

They form the outer layer and provide structural integrity.

How do lifestyle changes affect lipid levels in the body?

Improvements in diet and exercise can lower LDL and raise HDL.

What type of cellular response occurs when cholesterol levels in cells are high?

Decreased synthesis of new cholesterol and increased uptake of LDL.

Explain the water solubility challenges associated with cholesterol.

Cholesterol is hydrophobic and requires lipoproteins for transport in the bloodstream.

What is the primary method the body uses to regulate cholesterol levels?

Feedback inhibition of cholesterol synthesis and uptake.

Describe the conversion pathway of cholesterol to steroid hormones.

Cholesterol is converted through several enzymatic steps to produce various steroids.

What factors can influence lipoprotein metabolism during intense physical activity?

Increased lipolysis and enhanced transport of fatty acids for energy.

What role does estrogen play in metabolic processes?

It influences fat distribution and insulin sensitivity.

What is the catastrophic effect of missing or non-functional LDL receptors in familial hypercholesterolemia?

It leads to severe hypercholesterolemia due to impaired cholesterol uptake.

What functions do bile salts serve beyond fat digestion?

They also assist in the absorption of fat-soluble vitamins.

What is a key characteristic of sphingomyelin?

It contains phosphorylcholine as a substituent.

Discuss the relationship of serum triglycerides to cardiovascular risk.

High serum triglycerides are linked to increased cardiovascular risk.

Define hyperlipidemia.

An abnormally high concentration of lipids in the blood.

What significance does VLDL have in the lipid profile?

VLDL is a carrier for triglycerides that influence blood lipids when elevated.

How do chylomicrons function differently from LDL?

Chylomicrons transport dietary lipids, while LDL transports endogenous cholesterol.

What happens in the liver when excess triglycerides are exported in VLDL?

The liver synthesizes and secretes more VLDL while regulating cholesterol levels.

What is the dependence of lipoprotein function on apolipoproteins?

Apolipoproteins are essential for lipid solubility, receptor interactions, and enzyme modulation.

What environmental factors are influential in lipid levels management?

Diet, exercise patterns, and overall lifestyle choices.

How does the body handle excess cholesterol?

It is either stored in tissues or excreted via bile salts.

What clinical implications arise from disturbances in lipid metabolism?

They can lead to cardiovascular diseases, diabetes, and metabolic syndrome.

What biomarkers indicate lipid-related conditions?

Cholesterol levels, triglycerides, and the ratio of LDL to HDL.