Molecular Cell Biology Exam 1-- 2024 | ALL CURRENT EXAM VERSIONS 2024 | ACCURATE REAL EXAM QUESTIONS AND ANSWERS | ACCURATE AND VERIFIED FOR GUARANTEED PASS | GRADED A

1. Fatty Acids are made from Acetyl CoA by what two cytosolic enzymes? A) Acetyl-CoA Carboxylase and Fatty Acid Synthase B) Acetyl-CoA Carboxylase and Carnitine Acyltransferase C) Acyl-CoA Synthetase and Fatty Acid Synthase D) Glycerol Kinase and Acetyl-CoA Carboxylase Correct Answer: A) Acetyl-CoA Carboxylase and Fatty Acid Synthase Rationale: Acetyl-CoA Carboxylase and Fatty Acid Synthase are the enzymes responsible for the synthesis of fatty acids from Acetyl-CoA in the cytosol. 2. What do Desaturase enzymes do? Where are they located? A) Introduce double bonds; located in the ER B) Remove double bonds; located in the Golgi C) Introduce hydroxyl groups; located in the mitochondria D) Add methyl groups; located in the cytosol Correct Answer: A) Introduce double bonds; located in the ER Rationale: Desaturases are enzymes that introduce double bonds into fatty acids and are located in the endoplasmic reticulum (ER). 3. Where are diacylglycerophospholipids synthesized? A) Golgi B) Mitochondria C) ER D) Nucleus Correct Answer: C) ER Rationale: Diacylglycerophospholipids are synthesized in the endoplasmic reticulum (ER). 4. Where are sphingosine and N-acyl sphingosine synthesized? A) Golgi B) Mitochondria C) ER D) Cytosol Correct Answer: C) ER Rationale: Both sphingosine and N-acyl sphingosine are synthesized in the endoplasmic reticulum (ER). 5. Where does the addition of a polar head group to ceramide take place? A) Golgi B) Mitochondria C) ER D) Cytosol Correct Answer: A) Golgi Rationale: The addition of a polar head group to ceramide to form sphingolipids occurs in the Golgi apparatus. 6. How do fatty acids move around? A) Bound to fatty acid binding proteins; fatty acid binding proteins that have a beta-sheet pocket B) By diffusion across the membrane C) By binding to cholesterol D) In vesicles Correct Answer: A) Bound to fatty acid binding proteins; fatty acid binding proteins that have a beta-sheet pocket Rationale: Fatty acids move around in the cytosol bound to fatty acid binding proteins, which have a beta-sheet structure for efficient binding. 7. What is the first step of phospholipid synthesis? A) Acetyl-CoA is converted to a fatty acid by acetyl-CoA carboxylase and fatty acid synthase B) Diacylglycerol is converted to phosphatidylcholine C) Phosphatidic acid is formed D) Glycerol is phosphorylated to form G3P Correct Answer: A) Acetyl-CoA is converted to a fatty acid by acetyl-CoA carboxylase and fatty acid synthase Rationale: The first step of phospholipid synthesis is the conversion of Acetyl-CoA into a fatty acid by the enzymes acetyl-CoA carboxylase and fatty acid synthase. 8. What is the second step of phospholipid synthesis? A) Acetyl-CoA + G3P --> Phosphatidic acid B) Fatty acid + CoA --> Fatty acyl CoA C) Diacylglycerol + choline --> Phosphatidylcholine D) Phosphatidic acid --> Diacylglycerol Correct Answer: B) Fatty acid + CoA --> Fatty acyl CoA Rationale: In the second step of phospholipid synthesis, fatty acids combine with CoA to form fatty acyl CoA. 9. What is the third step of phospholipid synthesis? A) Glycerol is converted to G3P B) Fatty acyl CoA esterified with glycerol phosphate to create Phosphatidic acid C) Phosphatidic acid is converted to diacylglycerol D) Fatty acid is introduced to a glycerol molecule Correct Answer: B) Fatty acyl CoA esterified with glycerol phosphate to create Phosphatidic acid Rationale: The third step involves the esterification of fatty acyl CoA with glycerol phosphate to form phosphatidic acid. 10. Phosphatidic acid is converted to what molecule by which enzyme? A) Phosphatidylcholine by choline phosphotransferase B) Diacylglycerol by phosphatase C) Sphingomyelin by sphingomyelinase D) Glycerol by glycerol kinase Correct Answer: B) Diacylglycerol by phosphatase Rationale: Phosphatidic acid is dephosphorylated to diacylglycerol by the action of phosphatase. 11. What does phosphatase do? Where is it located? A) Transfers a phosphate group; located in the ER B) Removes a phosphate group; located in the ER membrane C) Adds a phosphate group; located in the Golgi D) Breaks down lipids; located in the cytosol Correct Answer: B) Removes a phosphate group; located in the ER membrane Rationale: Phosphatases remove phosphate groups and are located in the ER membrane. 12. Phosphatidic acid is basically? A) A glycerol-based molecule with a head group B) A phospholipid without a head group C) A free fatty acid D) A protein-bound lipid Correct Answer: B) A phospholipid without a head group Rationale: Phosphatidic acid is essentially a phospholipid without the addition of a polar head group. 13. Diacylglycerol is converted to what by which enzyme? A) Phosphatidylcholine by choline phosphotransferase B) Phosphatidylserine by serine phosphotransferase C) Phosphatidic acid by phosphatase D) Phosphatidylglycerol by glycerol kinase Correct Answer: A) Phosphatidylcholine by choline phosphotransferase Rationale: Diacylglycerol is converted to phosphatidylcholine by the enzyme choline phosphotransferase. 14. What do flippases do? A) Catalyze movement of phospholipids from cytosolic leaflet to exoplasmic leaflet B) Break down lipids in the membrane C) Transport fatty acids into the mitochondria D) Synthesize phospholipids in the ER Correct Answer: A) Catalyze movement of phospholipids from cytosolic leaflet to exoplasmic leaflet Rationale: Flippases help in the movement of phospholipids between leaflets of the membrane. 15. What enzyme converts Glycerol phosphate + fatty acyl CoA to phosphatidic acid? A) Acyl transferases, by GPAT/LPAAT located in the ER membrane B) Phosphatase in the Golgi C) Phosphotransferase in the mitochondria D) Acyl-CoA synthetase in the cytosol Correct Answer: A) Acyl transferases, by GPAT/LPAAT located in the ER membrane Rationale: The enzymes acyl transferases (GPAT/LPAAT) in the ER membrane convert glycerol phosphate and fatty acyl CoA to phosphatidic acid. 16. Where is HMG-CoA synthesized? A) Mitochondria B) Cytosol C) Golgi D) Nucleus Correct Answer: B) Cytosol Rationale: HMG-CoA is synthesized in the cytosol. 17. What is the rate-limiting step of cholesterol biosynthesis? A) Acetyl-CoA carboxylase B) HMG-CoA reductase C) Mevalonate synthase D) Farnesyl pyrophosphate synthase Correct Answer: B) HMG-CoA reductase Rationale: HMG-CoA reductase catalyzes the rate-limiting step in cholesterol biosynthesis. 18. Where is HMG-CoA reductase located? What is its structure? A) Mitochondria; alpha-helix structure B) ER membrane; 8 transmembrane helices embedded in the membrane, 5 forming a sterol-sensing domain C) Cytosol; 4 alpha-helices D) Nucleus; beta-sheet structure Correct Answer: B) ER membrane; 8 transmembrane helices embedded in the membrane, 5 forming a sterol-sensing domain Rationale: HMG-CoA reductase is located in the ER membrane with a structure featuring 8 transmembrane helices, and a sterol-sensing domain. 19. What happens when cholesterol levels are high? A) Cholesterol stimulates the synthesis of HMG-CoA reductase B) Cholesterol binds to the sterol-sensing domain of HMG-Reductase, induces it to bind to Insig-1 and Insig-2, leading to degradation C) Cholesterol activates the enzyme phospholipase D) Cholesterol promotes the synthesis of more cholesterol Correct Answer: B) Cholesterol binds to the sterol-sensing domain of HMG-Reductase, induces it to bind to Insig-1 and Insig-2, leading to degradation Rationale: When cholesterol levels are high, it binds to HMG-CoA reductase, leading to its degradation via binding to Insig-1 and Insig-2. 20. What is Atherosclerosis? A) Accumulation of glucose in blood vessels B) Deposition of lipids, cholesterol, and extracellular material in the inner wall of arteries C) Increased blood flow to arteries D) A condition where cholesterol is broken down in the liver Correct Answer: B) Deposition of lipids, cholesterol, and extracellular material in the inner wall of arteries Rationale: Atherosclerosis is the buildup of lipids, cholesterol, and other material inside artery walls, which can lead to clots.