Question 1

In prokaryotes, _________ is used exclusively as the precursor for phosphatidic acid while in eukaryotes, _________is one of three possible precursors.

Accepted Answer

In prokaryotes, diacylglycerol (DAG) is used exclusively as the precursor for phosphatidic acid. In eukaryotes, glycerol-3-phosphate (G3P), dihydroxyacetone phosphate (DHAP), or DAG can be used as precursors for phosphatidic acid. However, G3P is the most common precursor in eukaryotes. Therefore, option B is the best choice as it correctly identifies G3P as a precursor in eukaryotes and distinguishes it from the situation in prokaryotes.

Question 2

How is the activity of HMG-CoA reductase reduced?

Accepted Answer

HMG-CoA reductase activity is reduced through ubiquitination in response to sterol accumulation, which targets the enzyme for proteolysis. This is a key regulatory mechanism to control cholesterol synthesis in cells.

Question 3

Which of the following is used to activate phosphatidic acid for conversion to various phospholipids?

Accepted Answer

CTP is used to activate phosphatidic acid for conversion to various phospholipids, facilitating the synthesis of phosphatidylcholine and phosphatidylethanolamine through the Kennedy pathway.

Question 4

Which of the following is accomplished in one enzyme catalyzed reaction?

Accepted Answer

The conversion of androstenedione to testosterone is accomplished in one enzyme-catalyzed reaction, specifically by the enzyme 17β-hydroxysteroid dehydrogenase.

Question 5

Phospholipids are synthesized in the ___________, then transferred to the ____________ via transport vesicles.

Accepted Answer

Phospholipids are synthesized in the smooth endoplasmic reticulum (SER) and then transferred to the Golgi complex via transport vesicles. The Golgi complex is responsible for further modification and sorting of the lipids before they are sent to their final destination, which could include the cell membrane or other organelles. Option B and C are incorrect because rough endoplasmic reticulum is primarily involved in protein synthesis and lysosomes contain hydrolytic enzymes. Option D is incorrect because the transfer of lipids is from the SER to the Golgi complex, not the other way around. Option E is partially correct, as the cell membrane can be a final destination for phospholipids, but it is not the only destination.

Question 6

The enzyme PGH synthase contains two different functionalities, a __________ that uses two molecules of oxygen as substrates and __________ which performs a 2 electron reduction.

Accepted Answer

PGH synthase contains two different functionalities, a cyclooxygenase that uses two molecules of oxygen as substrates and a peroxidase which performs a 2 electron reduction.

Question 7

What is the term for the molecule shown below?

Accepted Answer

The answer of What is the term for the molecule...

Question 8

Tay-Sachs disease is caused by a deficiency of __________ which results in an accumulation of ___________.

Accepted Answer

Tay-Sachs disease is caused by a deficiency of lysosomal N-acetylhexosaminidase A, which leads to an accumulation of GM2 ganglioside in the brain and other tissues.

Question 9

Which of the following forms of vitamin A is covalently attached to a lysine residue of the protein opsin to form the complex called rhodopsin?

Accepted Answer

11-cis-retinal is covalently attached to a lysine residue of the protein opsin to form the complex called rhodopsin.

Question 10

The synthesis of 1 molecule of cholesterol requires _____ molecules of isopentenyl pyrophosphate, with each molecule of isopentenyl pyrophosphate requiring _____ molecules of acetyl-CoA.

Accepted Answer

The synthesis of cholesterol requires 6 molecules of isopentenyl pyrophosphate, and each molecule of isopentenyl pyrophosphate is derived from 3 molecules of acetyl-CoA.

Question 11

Which of the following correctly identifies the order of carbocations found in the mechanism of squalene synthase?

Accepted Answer

The mechanism of squalene synthase involves the formation of an allylic carbocation first, followed by a tertiary carbocation, and finally a tertiary cyclopropylcarbinyl carbocation.

Question 12

Which of the following phospholipids is produced in eukaryotes but not prokaryotes?

Accepted Answer

Phosphatidylinositol is a phospholipid that is specifically produced in eukaryotic cells and plays a key role in cell signaling and membrane structure. Prokaryotes do not synthesize phosphatidylinositol.

Question 13

Which of the following is the regulatory step in cholesterol synthesis?

Accepted Answer

HMG-CoA reductase is the regulatory step in cholesterol synthesis, as it is the enzyme that converts HMG-CoA into mevalonate, which is the first committed step in the pathway. This step is tightly regulated by feedback inhibition from cholesterol and other sterols.

Question 14

7-dehydrocholesterol reacts with _________ to produce cholecalciferol (vitamin D₃)

Accepted Answer

7-dehydrocholesterol undergoes a photochemical reaction with UV light to produce cholecalciferol (vitamin D3). The UV light causes the bond between carbon 9 and 10 to break and form a double bond, resulting in the conversion of 7-dehydrocholesterol into cholecalciferol.

Question 15

Which of the following explains why the bile acids are much better suited than cholesterol for use as emulsification agents for fats?

Accepted Answer

All the choices explain why bile acids are better emulsification agents compared to cholesterol. They describe the modifications that increase the polarity and hydrophilic properties of bile acids, making them more effective in emulsifying fats.

Question 16

Which of the following amino acids is critical for choline and phosphatidylcholine synthesis?

Accepted Answer

Methionine is critical for choline and phosphatidylcholine synthesis as it is a precursor for S-adenosylmethionine (SAM), which is the primary methyl donor for the biosynthesis of phosphatidylcholine.

Question 17

Squalene epoxidase is an example of a mixed function oxidase, meaning that it uses both _______ and _______ as substrates.

Accepted Answer

Squalene epoxidase is an enzyme involved in the synthesis of cholesterol and uses oxygen and NADPH as substrates. Therefore, the best choice is E.

Question 18

The biosynthesis of cardiolipin involves the reaction of phosphatidylglycerol with a molecule of ___________.

Accepted Answer

Cardiolipin biosynthesis involves the reaction of phosphatidylglycerol with another molecule of phosphatidylglycerol, leading to the formation of cardiolipin and a molecule of glycerol.

Question 19

The synthesis of phosphatidylethanolamine in prokaryotes involves _________________ while in mammals _______________ occurs.

Accepted Answer

In prokaryotes, phosphatidylethanolamine is synthesized by the decarboxylation of phosphatidylserine. In mammals, it is synthesized by the reaction of CDP-ethanolamine with diacylglycerol.

Question 20

The synthesis of the glycosphingolipids begins with the reaction of either UDP-glucose or UDP-galactose with _____________.

Accepted Answer

The synthesis of glycosphingolipids is initiated by the reaction of either UDP-glucose or UDP-galactose with ceramide. This reaction is catalyzed by the enzyme UDP-galactose ceramide galactosyltransferase or UDP-glucose ceramide glucosyltransferase, depending on the sugar involved. Sphinganine, sphingosine, and sphingomyelin are not involved in the synthesis of glycosphingolipids.

Quiz 19: Lipid Metabolism Ii: Membrane Lipids, Steroids, Isoprenoids, and Eicosanoids

In prokaryotes, _ is used exclusively as the precursor for phosphatidic acid while in eukaryotes, _is one of three possible precursors.

How is the activity of HMG-CoA reductase reduced?

Which of the following is used to activate phosphatidic acid for conversion to various phospholipids?

Which of the following is accomplished in one enzyme catalyzed reaction?

Phospholipids are synthesized in the _, then transferred to the __ via transport vesicles.

The enzyme PGH synthase contains two different functionalities, a that uses two molecules of oxygen as substrates and which performs a 2 electron reduction.

What is the term for the molecule shown below?

Tay-Sachs disease is caused by a deficiency of which results in an accumulation of _.

Which of the following forms of vitamin A is covalently attached to a lysine residue of the protein opsin to form the complex called rhodopsin?

The synthesis of 1 molecule of cholesterol requires _ molecules of isopentenyl pyrophosphate, with each molecule of isopentenyl pyrophosphate requiring _ molecules of acetyl-CoA.

Which of the following correctly identifies the order of carbocations found in the mechanism of squalene synthase?

Which of the following phospholipids is produced in eukaryotes but not prokaryotes?

Which of the following is the regulatory step in cholesterol synthesis?

7-dehydrocholesterol reacts with _________ to produce cholecalciferol (vitamin D₃)

Which of the following explains why the bile acids are much better suited than cholesterol for use as emulsification agents for fats?

Which of the following amino acids is critical for choline and phosphatidylcholine synthesis?

Squalene epoxidase is an example of a mixed function oxidase, meaning that it uses both _ and _ as substrates.

The biosynthesis of cardiolipin involves the reaction of phosphatidylglycerol with a molecule of ___________.

The synthesis of phosphatidylethanolamine in prokaryotes involves ___ while in mammals _ occurs.

The synthesis of the glycosphingolipids begins with the reaction of either UDP-glucose or UDP-galactose with _____________.

Quiz 19: Lipid Metabolism Ii: Membrane Lipids, Steroids, Isoprenoids, and Eicosanoids

In prokaryotes, _________ is used exclusively as the precursor for phosphatidic acid while in eukaryotes, _________is one of three possible precursors.

How is the activity of HMG-CoA reductase reduced?

Which of the following is used to activate phosphatidic acid for conversion to various phospholipids?

Which of the following is accomplished in one enzyme catalyzed reaction?

Phospholipids are synthesized in the ___________, then transferred to the ____________ via transport vesicles.

The enzyme PGH synthase contains two different functionalities, a __________ that uses two molecules of oxygen as substrates and __________ which performs a 2 electron reduction.

What is the term for the molecule shown below?

Tay-Sachs disease is caused by a deficiency of __________ which results in an accumulation of ___________.

Which of the following forms of vitamin A is covalently attached to a lysine residue of the protein opsin to form the complex called rhodopsin?

The synthesis of 1 molecule of cholesterol requires _____ molecules of isopentenyl pyrophosphate, with each molecule of isopentenyl pyrophosphate requiring _____ molecules of acetyl-CoA.

Which of the following correctly identifies the order of carbocations found in the mechanism of squalene synthase?

Which of the following phospholipids is produced in eukaryotes but not prokaryotes?

Which of the following is the regulatory step in cholesterol synthesis?

7-dehydrocholesterol reacts with _________ to produce cholecalciferol (vitamin D3)

Which of the following explains why the bile acids are much better suited than cholesterol for use as emulsification agents for fats?

Which of the following amino acids is critical for choline and phosphatidylcholine synthesis?

Squalene epoxidase is an example of a mixed function oxidase, meaning that it uses both _______ and _______ as substrates.

The biosynthesis of cardiolipin involves the reaction of phosphatidylglycerol with a molecule of ___________.

The synthesis of phosphatidylethanolamine in prokaryotes involves _________________ while in mammals _______________ occurs.

The synthesis of the glycosphingolipids begins with the reaction of either UDP-glucose or UDP-galactose with _____________.

In prokaryotes, _ is used exclusively as the precursor for phosphatidic acid while in eukaryotes, _is one of three possible precursors.

Phospholipids are synthesized in the _, then transferred to the __ via transport vesicles.

The enzyme PGH synthase contains two different functionalities, a that uses two molecules of oxygen as substrates and which performs a 2 electron reduction.

Tay-Sachs disease is caused by a deficiency of which results in an accumulation of _.

The synthesis of 1 molecule of cholesterol requires _ molecules of isopentenyl pyrophosphate, with each molecule of isopentenyl pyrophosphate requiring _ molecules of acetyl-CoA.

7-dehydrocholesterol reacts with _________ to produce cholecalciferol (vitamin D₃)

Squalene epoxidase is an example of a mixed function oxidase, meaning that it uses both _ and _ as substrates.

The synthesis of phosphatidylethanolamine in prokaryotes involves ___ while in mammals _ occurs.