WBR270
| Author | [[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::A 3year-old male was brought to the physician’s office with a 3-day history of fever, cough and runny nose. The mother complained that the child stopped growing over one year ago. Physical examination reveals generalized hypotonia, restricted joint movements and coarse facial features.
Radiologic findings include bullet-shaped phalanges, wedging of the vertebrae and widening of the ribs. Which is true about the cellular organelle involved in this condition?]] |
| Answer A | AnswerA::It is involved in the addition of O-oligosaccharides to serine and threonine residues |
| Answer A Explanation | AnswerAExp::Correct: See Explanation |
| Answer B | AnswerB::Modification of N-oligosaccharides on glycine |
| Answer B Explanation | AnswerBExp::Incorrect: Modification of N-oligosaccharides is on asparagine |
| Answer C | AnswerC::Addition of glucose -6-phosphate to specific lysosomal proteins |
| Answer C Explanation | AnswerCExp::Incorrect: It is the addition of mannose-6-phosphate to specific lysosomal proteins |
| Answer D | AnswerD::It is a distribution center of proteins and lipids from the endoplasmic reticulum to the mitochondria |
| Answer D Explanation | AnswerDExp::Incorrect: It is a distribution center of proteins and lipids from the endoplasmic reticulum to the plasma membrane, lysosomes and secretory vesicles |
| Answer E | AnswerE::It is involved in proteoglycan assembly from prelysosomes |
| Answer E Explanation | AnswerEExp::Incorrect: It is involved in proteoglycan assembly from core proteins |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::The is a case of Inclusion cell disease (I-cell disease) which is an inherited lysosomal storage disorder due to failure of addition of mannose -6- phosphate to lysosome proteins. It usually results in coarse facial features, clouded corneas, restricted joint movement and most of the time, it is fatal in childhood. The cellular organelle involved in this disease is the Golgi apparatus. It is a distribution center of proteins and lipids from the endoplasmic reticulum (ER) to the plasma membrane, lysosomes, and secretory vesicles. It modifies N-oligosaccharides on asparagine and adds O-oligosaccharides to serine and threonine residues. Proteoglycan assembly is from core proteins and involved in the sulfation of sugars in proteoglycans and of selected tyrosine on proteins. Addition of mannose-6-phosphate to specific lysosomal proteins would eventually target the protein to the lysosome.
Reference: First AID for the USMLE Step 1 2011 Pg 77 |
| Approved | Approved::Yes |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |