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Questions and Answers
Chylomicrons are the largest lipoprotein particles.
Chylomicrons are the largest lipoprotein particles.
True
VLDLs have a higher density than HDLs.
VLDLs have a higher density than HDLs.
False
LDLs are formed from the breakdown of VLDLs.
LDLs are formed from the breakdown of VLDLs.
True
Chylomicrons are primarily responsible for transporting cholesterol.
Chylomicrons are primarily responsible for transporting cholesterol.
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The density of VLDLs is between 0.95 and 1.006.
The density of VLDLs is between 0.95 and 1.006.
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HDLs have a smaller diameter than VLDLs.
HDLs have a smaller diameter than VLDLs.
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During starvation, ketone bodies become the major source of fuel for the brain.
During starvation, ketone bodies become the major source of fuel for the brain.
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Acetoacetate, being a β-keto acid, undergoes decarboxylation to acetone and CO2.
Acetoacetate, being a β-keto acid, undergoes decarboxylation to acetone and CO2.
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Cholesterol is a highly hydrophilic compound.
Cholesterol is a highly hydrophilic compound.
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The steroid nucleus of cholesterol consists of 3 fused rings.
The steroid nucleus of cholesterol consists of 3 fused rings.
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Cholesterol has an 8-carbon, branched hydrocarbon chain attached to C-17 of the D ring.
Cholesterol has an 8-carbon, branched hydrocarbon chain attached to C-17 of the D ring.
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Ring A of cholesterol has a hydroxyl group at C-4.
Ring A of cholesterol has a hydroxyl group at C-4.
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Cholesterol is the precursor of bile acids, steroid hormones, and vitamin D in specialized tissues.
Cholesterol is the precursor of bile acids, steroid hormones, and vitamin D in specialized tissues.
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The liver plays a significant role in maintaining cholesterol homeostasis in the body.
The liver plays a significant role in maintaining cholesterol homeostasis in the body.
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Trioleoylglycerol is composed of 3 oleic acid residues.
Trioleoylglycerol is composed of 3 oleic acid residues.
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Mixed TGs contain only one type of fatty acid residues.
Mixed TGs contain only one type of fatty acid residues.
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Glycerophospholipids are the major lipid components of biological membranes.
Glycerophospholipids are the major lipid components of biological membranes.
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Phosphatidic acid is the most complex type of phosphoglyceride.
Phosphatidic acid is the most complex type of phosphoglyceride.
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Shingophospholipids have glycerol as their backbone.
Shingophospholipids have glycerol as their backbone.
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Phosphatidylserine is formed from phosphatidic acid and ethanolamine.
Phosphatidylserine is formed from phosphatidic acid and ethanolamine.
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Sphingomyelin is not a significant shingophospholipid in humans.
Sphingomyelin is not a significant shingophospholipid in humans.
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Lipoproteins are soluble in water.
Lipoproteins are soluble in water.
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The nonpolar core of lipoproteins is composed mainly of phospholipids.
The nonpolar core of lipoproteins is composed mainly of phospholipids.
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There are three main types of lipoproteins based on their density.
There are three main types of lipoproteins based on their density.
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Apolipoprotein refers to the protein component of lipoproteins.
Apolipoprotein refers to the protein component of lipoproteins.
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The polar groups of lipoproteins face inward towards the nonpolar core.
The polar groups of lipoproteins face inward towards the nonpolar core.
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Lipids are soluble in water when they are in their free form.
Lipids are soluble in water when they are in their free form.
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Lipoprotein particles vary in density, size, and lipid composition.
Lipoprotein particles vary in density, size, and lipid composition.
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Cholesterol is essential for human life but not required in diets.
Cholesterol is essential for human life but not required in diets.
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The biosynthetic process of cholesterol involves a simple pathway requiring only one precursor.
The biosynthetic process of cholesterol involves a simple pathway requiring only one precursor.
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Mevalonate is formed from the condensation of three molecules of acetyl-CoA.
Mevalonate is formed from the condensation of three molecules of acetyl-CoA.
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NADPH acts as the reducing equivalent in cholesterol biosynthesis.
NADPH acts as the reducing equivalent in cholesterol biosynthesis.
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The first stage of cholesterol biosynthesis involves the reduction of HMG-CoA.
The first stage of cholesterol biosynthesis involves the reduction of HMG-CoA.
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3 phosphate groups from ATP are not required for forming mevalonate.
3 phosphate groups from ATP are not required for forming mevalonate.
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∆3-isopentenyl pyrophosphate is the second activated isoprene produced during cholesterol biosynthesis.
∆3-isopentenyl pyrophosphate is the second activated isoprene produced during cholesterol biosynthesis.
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The cholesterol biosynthesis pathway begins with the synthesis of acetoacetyl-CoA.
The cholesterol biosynthesis pathway begins with the synthesis of acetoacetyl-CoA.
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Study Notes
Triacylglycerols
- Trioleoylglycerol or triolein has 3 oleic acid residues
- Mixed triacylglycerols (TGs) contain 2 or 3 different types of fatty acid residues and are named according to their placement on the glycerol moiety
Phospholipids
- There are 2 classes of phospholipids: those with glycerol as a backbone (glycerophospholipids or phosphoglycerides) and those that contain sphingosine as a backbone (sphingophospholipids)
- Glycerophospholipids are the major lipid components of biological membranes
- Phosphatidic acid is the simplest phosphoglyceride and is the precursor of other members of this group
- Other phosphoglycerides are formed from phosphatidic acid (PA) and an alcohol, such as:
- PA + serine = phosphatidylserine
- PA + ethanolamine = phosphatidylethanolamine (cephalin)
- PA + choline = phosphatidylcholine (lecithin)
- PA + inositol = phosphatidylinositol
- PA + glycerol = phosphatidylglycerol
Sphingophospholipids: Sphingomyelin
- The backbone of sphingophospholipids is the amino alcohol sphingosine, rather than glycerol
- A long-chain fatty acid is attached to the amino group of sphingosine through an amide linkage, producing a ceramide
- The alcohol group of sphingosine is esterified to phosphorylcholine, producing sphingomyelin, the only significant sphingophospholipid in humans
- Sphingomyelin is an important constituent of the myelin of nerve fibers
Lipoproteins
- Lipids that are absorbed from the diet and synthesized by the liver and adipose tissue must be transported between cells and organs for effective utilization and storage
- Lipids are insoluble in water, so they are transported in the aqueous plasma (blood) by associating with amphipathic lipids (phospholipids and cholesterol) and proteins to form water-miscible lipoproteins
- Lipoproteins are spherical macromolecular complexes of lipids and proteins, consisting of a nonpolar core and a single surface layer of amphipathic lipids
- The nonpolar core consists mainly of triacylglycerol and cholesteryl ester, surrounded by a single surface layer of amphipathic phospholipid and cholesterol molecules
- The protein moiety of a lipoprotein is known as an apolipoprotein or apoprotein
Classification of Lipoproteins
- Lipoproteins differ in density, size, lipid and protein composition, and site of origin
- There are 4 lipoprotein particles:
- Chylomicrons
- Very-low-density lipoproteins (VLDL)
- Low-density lipoproteins (LDL)
- High-density lipoproteins (HDL)
- Chylomicrons are the largest lipoprotein particles, with the lowest density and highest percentage of lipid
- VLDLs and LDLs are successively denser, with higher ratios of protein to lipid
- HDL particles have the highest density
Cholesterol
- Cholesterol is a very hydrophobic compound consisting of 4 fused rings (A, B, C, and D) and an 8-carbon, branched hydrocarbon chain attached to C-17 of the D ring
- Ring A has a hydroxyl group at C-3, and ring B has a double bond between C-5 and C-6
- Cholesterol is a structural component of all cell membranes, where it modulates fluidity
- In specialized tissues, cholesterol is the precursor of bile acids, steroid hormones, and vitamin D
- The liver plays a central role in the regulation of the body's cholesterol homeostasis
Cholesterol Metabolism
- Cholesterol is essential to life, yet its deposition in arteries has been associated with cardiovascular disease and stroke
- In healthy individuals, a balance is maintained between cholesterol biosynthesis, utilization, and transport, ensuring that deposition in arteries is kept to a minimal level
- Cholesterol is not essential in human diets, because all cells can synthesize it from simple precursors
- Cholesterol biosynthesis involves the synthesis of mevalonate from acetate, followed by the conversion of mevalonate to 2 activated isoprenes
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Description
This quiz covers the different types of lipids, including triolein, mixed triglycerides, phospholipids, and their classifications. Learn about the glycerol and sphingosine backbones in lipids.
