BIOL331 Assignment – Heterozygous and homozygous

BIOL331-W17-VZ-AssignmentLearning goals1- to apply concepts and experimental approaches learned in lectures and tutorials to find answers/solutions toproblems you have not been previously exposed to,2- to expand your knowledge on receptor mediated endocytosis and movement of lipids in human cells,3- to strengthen your independent learning skills by challenging you to figure out a new cellular pathway viaanalysis of solid scientific evidence in combination with the use of appropriate resources.Terms you need to review and understand before tackling this assignment:From Genetics•• Heterozygous and homozygousDominant and recessive mutations From Biochemistry and Cell Biology• •• • Figure 1- Low density lipoprotein What is LDL (low density lipoprotein)? See Fig 1 andKarp (7th Ed) Chapter 8 Section 8.8 (Fig 8.44)Karp (8th Ed) Chapter 8 Section 8.19 (Fig 8.44)Human cells can uptake exogenous cholesterol packed inLDLCells can also make endogenous cholesterol using apathway that involves 27 different enzymes. The mostregulated step in this pathway is the one catalyzed by anenzyme called HMG-CoA reductase.When cholesterol inside the cell is low, the pathway isactivated, and when cholesterol is high, the pathway isinhibited. This regulation is called “feedback regulation”. From BIOL331 TutorialsRadioactive labeling. Iodination involves the introduction of radioactive iodine [125I] into certain amino acids(usually tyrosines) in proteinsFrom BIOL331 Lectures••• Endomembrane systemEndocytosisLysosomes Readings for this assignment•••••• The LDL receptor-JL Goldstein and MS Brown (2009) Arterioscler Thromb Vasc Biol; 29:431-438Karp (7th Ed) Chapter 8, Section 8.9 page 319 “Experimental pathways: Receptor-mediated Endocytosis”Karp (7th Ed) Chapter 8, Section 8.6 page 306 “The human perspective Disorders: resulting from defects inlysosomal function”Karp (8th Ed) Chapter 8, Section 8.18 page 297 “Experimental pathways: Receptor-mediated Endocytosis”Karp (8th Ed) Chapter 8, Section 8.12 page 286 “The human perspective Disorders: resulting from defectsin lysosomal function”VIDEO: ENDOCYTOSIS http://www.sumanasinc.com/webcontent/animations/content/endocytosis.html BIOL331-W17-VZ-AssignmentREADING MATERIAL:In order to answer the questions below read pages 431 to 435 of the review article “The LDL receptor” by JLGoldstein and MS Brown (2009) , Arterioscler Thromb Vasc Biol; 29:431-438.Do not need to read “Regulation of LDL receptors” in page 435 and page 436.Skip to page 437 and read the final paragraph entitled “The Legacy”.QUESTIONSAnswer the following 5 questions in D2L. Be concise and to the point limiting your answers to 70 words or less,except for question 3 where you can use a limit of 140 words. Grades will be deducted if the answer includessentences unrelated to the question asked.Q1- (5 points) Familial hypercholesterolemiaWhat is the main symptom of familial hypercholesterolemia (FH)?Explain why FH was thought to be linked to a mutation in a gene product that participated in the regulation ofcholesterol metabolism as opposed to an enzyme.Q2- (5 points) Cholesterol transportHow is cholesterol transported in the bloodstream of humans? What is “bad” and “good” cholesterol? Q3- (20 points) LDL uptake modelBrown and Goldstein obtained fibroblasts from patients homozygous for FH and were able to culture these cells inthe laboratory and compare their cholesterol uptake to normal fibroblasts. Incubation of normal cells withlabelled-LDL showed LDL is first bound to the cell and then internalized. But cells from FH patients were not able tobind LDL and it was never internalized.The researchers proposed the following model:(watch the animation http://www.sumanasinc.com/webcontent/animations/content/endocytosis.html ) Figure 2- LDL uptake model- Esterified cholesterol =Cholesteryl Linoleate or Cholesteryl OleateExplain steps 1 to 5 of the model. Which step is deficient in FH cells? Explain what happens to the LDL receptorafter it is internalized bound to LDL. BIOL331-W17-VZ-Assignment Q4- (15 points) J.D. caseThe studies shown in the figure below (Fig 3) were done using cells from an FH patient whose initials were J.D. Figure 3-Internalization and degradation at 37°C of 125I-LDL by fibroblasts from a normal subject (A) and fromJ.D., a patient with the internalization-defective form of FH (B). A. ( 2points) What part of the LDL lipoprotein was labelled with 125I for these studies?B. (3 points) What is the conclusion of this experiment?C. (10 points) How is this explained at the molecular level and what is the role of clathrin in this process? Q5- (10 points) Enzyme replacement therapyExplain the molecular mechanism/s involved in the delivery of enzymes (enzyme replacement therapy) for thetreatment of lysosomal storage disorders like Gaucher’s disease.Read:Karp (7th Ed) Chapter 8, Section 8.6 page 306 “The human perspective Disorders: resulting from defects inlysosomal function”Karp (8th Ed) Chapter 8, Section 8.12 page 286 “The human perspective Disorders: resulting from defects inlysosomal functionDEADLINE: Friday, February 17, 2017 at 5:00pm via D2L.

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