BBL LESSON 11: LIPIDS AND
CHOLESTEROL QUESTIONS AND
VERIFIED ANSWERS|100%
CORRECT|GRADE A+
Phospholipid - ANSWER Glycerol backbone with one or two fatty acid chains via ester linkages and to a
phosphate group. This basic lipid is called phosphatidic acid. In some cases, different polar headgroups
can be added to the other end of the phosphate group, forming different phospholipids. There are five
different headgroups and thus there exist six different phospholipids that are glycerol based.
Sphingomyelin - ANSWER Lipid which has one fatty acid attached to sphingosine via an amide bond and a
phosphate group attached to the sphingosine group, hence it is a phospholipid. Important for animal cell
membranes; it is a major component of the myelin sheath of nerve cell axons and it acts as an electrical
insulator. It is also a cell signaling molecule and plays a role in cell death or apoptosis.
Sphingosine-based lipids - ANSWER Glycolipids or cerebrosides. These
lipids have a sugar headgroup but no phosphate group and hence are not phospholipids. Like
sphingomyelin, glycolipids are common in nerve cell membranes.
Cholesterol - ANSWER Mediates the state of the membrane bilayer. It inserts itself between the
phospholipids. The OH group of the cholesterol molecule is positioned near the head groups of the
phospholipids. The hydrophobic ring and aliphatic chain regions are inserted into the hydrophobic region
of the membrane bilayer where the fatty acid chains reside. Basically maintains a fairly constant
membrane fluidity or state, despite any changes in temperature. This ensures that the cell maintains its
membrane bilayer in a constant, stable state and does not melt or become too stiff when temperatures
fluctuate.
Cholesterol Structure - ANSWER Consists of a tetracyclic cyclopenta[a]phenanthrene structure with an
iso-octyl side-chain at carbon 17. The four rings (A, B, C, D) have trans ring junctions, and the side chain
and two methyl groups (C-18 and C-19) are at an angle to the rings above the plane with β
stereochemistry (as for the hydroxyl group on C-3 also). There is a double bond between carbons 5 and
6. Thus, the molecule has a rigid planar four-ring nucleus with a flexible tail.
, Cholesterol as a Precursor - ANSWER Precursor for the synthesis of bile salts, steroids, and Vitamin D;
also a component of lipoprotein complexes which we will describe in more detail later in this
presentation. The body needs to periodically reduce systemic levels. This is achieved by converting
cholesterol into water soluble forms by the addition of hydroxyl and charged groups. This conversion
takes place in the liver and the soluble forms are known as bile salts or bile acids. The major bile salt is
cholic acid and this is also a precursor for other bile salts.
Bile Salts - ANSWER Moved from the liver to the gallbladder where they are stored until needed. Once
the digestive process has started, they are released from the gallbladder into the small intestine. Here
they combine with dietary triacylglycerides and cholesterol, forming a water soluble emulsion that can
travel through the bloodstream to the liver where the fats and cholesterol will be processed. Once this is
done, they are excreted in the urine.
Steroid Synthesis - ANSWER Cholesterol also acts as a precursor for the synthesis of steroids. The
synthesis process involves P450 enzymes which add different chemical groups or modify existing groups
on the cholesterol molecule and thus make them recognition responsive to other proteins. These
conversion processes take place in several tissues.
What is the first step of steroid synthesis? - ANSWER The conversion of cholesterol into progesterone.
Once progesterone is made, it can be further processed and converted.
Where does the first step of steroid synthesis take place? - ANSWER The adrenal cortex, and the sex
organs, testes or ovaries.
What is progesterone converted into? - ANSWER In the testes and ovaries, it is converted into
testosterone and estradiol. In the adrenal cortex, it is converted into aldosterone and cortisol.
Vitamin D Synthesis - ANSWER Cholesterol precursor. 1. In skin, cholesterol converted into 7-
dehydrocholesterol using sunlight. 2. 7-dehydrocholesterol travels to liver where it is converted into
vitamin D3 precursor. 3. Endogenous or exogenous vitamin D3 precursor then converted into 25-hydroxy
vitamin D3 in liver. 4. This form travels to Kidney where it is converted into major Vitamin D form (1, 25-
dihydroxyvitamin D3.)
What is the major function of Vitamin D3? - ANSWER Maintains calcium homeostasis in the body.
CHOLESTEROL QUESTIONS AND
VERIFIED ANSWERS|100%
CORRECT|GRADE A+
Phospholipid - ANSWER Glycerol backbone with one or two fatty acid chains via ester linkages and to a
phosphate group. This basic lipid is called phosphatidic acid. In some cases, different polar headgroups
can be added to the other end of the phosphate group, forming different phospholipids. There are five
different headgroups and thus there exist six different phospholipids that are glycerol based.
Sphingomyelin - ANSWER Lipid which has one fatty acid attached to sphingosine via an amide bond and a
phosphate group attached to the sphingosine group, hence it is a phospholipid. Important for animal cell
membranes; it is a major component of the myelin sheath of nerve cell axons and it acts as an electrical
insulator. It is also a cell signaling molecule and plays a role in cell death or apoptosis.
Sphingosine-based lipids - ANSWER Glycolipids or cerebrosides. These
lipids have a sugar headgroup but no phosphate group and hence are not phospholipids. Like
sphingomyelin, glycolipids are common in nerve cell membranes.
Cholesterol - ANSWER Mediates the state of the membrane bilayer. It inserts itself between the
phospholipids. The OH group of the cholesterol molecule is positioned near the head groups of the
phospholipids. The hydrophobic ring and aliphatic chain regions are inserted into the hydrophobic region
of the membrane bilayer where the fatty acid chains reside. Basically maintains a fairly constant
membrane fluidity or state, despite any changes in temperature. This ensures that the cell maintains its
membrane bilayer in a constant, stable state and does not melt or become too stiff when temperatures
fluctuate.
Cholesterol Structure - ANSWER Consists of a tetracyclic cyclopenta[a]phenanthrene structure with an
iso-octyl side-chain at carbon 17. The four rings (A, B, C, D) have trans ring junctions, and the side chain
and two methyl groups (C-18 and C-19) are at an angle to the rings above the plane with β
stereochemistry (as for the hydroxyl group on C-3 also). There is a double bond between carbons 5 and
6. Thus, the molecule has a rigid planar four-ring nucleus with a flexible tail.
, Cholesterol as a Precursor - ANSWER Precursor for the synthesis of bile salts, steroids, and Vitamin D;
also a component of lipoprotein complexes which we will describe in more detail later in this
presentation. The body needs to periodically reduce systemic levels. This is achieved by converting
cholesterol into water soluble forms by the addition of hydroxyl and charged groups. This conversion
takes place in the liver and the soluble forms are known as bile salts or bile acids. The major bile salt is
cholic acid and this is also a precursor for other bile salts.
Bile Salts - ANSWER Moved from the liver to the gallbladder where they are stored until needed. Once
the digestive process has started, they are released from the gallbladder into the small intestine. Here
they combine with dietary triacylglycerides and cholesterol, forming a water soluble emulsion that can
travel through the bloodstream to the liver where the fats and cholesterol will be processed. Once this is
done, they are excreted in the urine.
Steroid Synthesis - ANSWER Cholesterol also acts as a precursor for the synthesis of steroids. The
synthesis process involves P450 enzymes which add different chemical groups or modify existing groups
on the cholesterol molecule and thus make them recognition responsive to other proteins. These
conversion processes take place in several tissues.
What is the first step of steroid synthesis? - ANSWER The conversion of cholesterol into progesterone.
Once progesterone is made, it can be further processed and converted.
Where does the first step of steroid synthesis take place? - ANSWER The adrenal cortex, and the sex
organs, testes or ovaries.
What is progesterone converted into? - ANSWER In the testes and ovaries, it is converted into
testosterone and estradiol. In the adrenal cortex, it is converted into aldosterone and cortisol.
Vitamin D Synthesis - ANSWER Cholesterol precursor. 1. In skin, cholesterol converted into 7-
dehydrocholesterol using sunlight. 2. 7-dehydrocholesterol travels to liver where it is converted into
vitamin D3 precursor. 3. Endogenous or exogenous vitamin D3 precursor then converted into 25-hydroxy
vitamin D3 in liver. 4. This form travels to Kidney where it is converted into major Vitamin D form (1, 25-
dihydroxyvitamin D3.)
What is the major function of Vitamin D3? - ANSWER Maintains calcium homeostasis in the body.
