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Rim Halaby (talk | contribs) (Created page with "{{WBRQuestion |QuestionAuthor={{Rim}} |ExamType=USMLE Step 1 |MainCategory=Biochemistry |SubCategory=General Principles |MainCategory=Biochemistry |SubCategory=General Princip...") |
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|SubCategory=General Principles | |SubCategory=General Principles | ||
|Prompt=A pregnant woman known to have classic galactokinase deficiency is worried she will not be able to breastfeed her baby because she has been on a strict galactose free diet since her birth. The physician comforts her and tells her that she will be having normal breast milk for lactation. The ability of the mammary glands to synthesize milk in the absence of dietary galactose in this patient is due to the activity of which of the following enzymes? | |Prompt=A pregnant woman known to have classic galactokinase deficiency is worried she will not be able to breastfeed her baby because she has been on a strict galactose free diet since her birth. The physician comforts her and tells her that she will be having normal breast milk for lactation. The ability of the mammary glands to synthesize milk in the absence of dietary galactose in this patient is due to the activity of which of the following enzymes? | ||
|Explanation=The patient suffers from galactokinase deficiency, a genetic disease of the galactose metabolism. Patients with galactokinase deficiency are required to have a galactose free diet to avoid the accumulation of galacticol. Even in the absence of dietary galactose, the endogenous synthesis of galactose occurs in the body. Galactose is produced in the form of UDP galactose through the activity of the epimerase enzyme on UDP glucose. The synthesis of lactose (milk) in the mammary glands results from the activity of lactose synthase on UDP galactose and glucose. | |Explanation=The patient suffers from [[galactokinase deficiency]], a genetic disease of the [[galactose]] metabolism. Patients with galactokinase deficiency are required to have a galactose free diet to avoid the accumulation of [[galacticol]]. Even in the absence of dietary galactose, the endogenous synthesis of galactose occurs in the body. Galactose is produced in the form of UDP galactose through the activity of the [[epimerase]] enzyme on UDP glucose. The synthesis of lactose (milk) in the [[mammary glands]] results from the activity of lactose synthase on UDP galactose and glucose. | ||
Learning objective: | Learning objective: | ||
Even in the absence of dietary galactose, the endogenous synthesis of galactose occurs in the body through the activity of the epimerase enzyme on UDP glucose. | Even in the absence of dietary galactose, the endogenous synthesis of galactose occurs in the body through the activity of the epimerase enzyme on UDP glucose. | ||
Reference: Shcwarz V. Disorders of galactose metabolism. Journal of clinical pathology (1969). | Reference: Shcwarz V. Disorders of galactose metabolism. Journal of clinical pathology (1969). | ||
|AnswerA=Aldose reductase | |AnswerA=Aldose reductase | ||
|AnswerAExp=[[Aldose reductase]] catalyzes the conversion of [[galactose]] to [[galacticol]] and glucose to sorbitol. It is not involved in the synthesis of galactose or lactose. | |||
|AnswerAExp=Aldose reductase catalyzes the conversion of galactose to galacticol and glucose to sorbitol. It is not involved in the synthesis of galactose or lactose. | |||
|AnswerB=Galactokinase | |AnswerB=Galactokinase | ||
|AnswerBExp=Galactokinase catalyzes the conversion of galactose to galactokinase 1 phosphate. The enzyme is already deficient in this patient and it is not directly involved in the synthesis of lactose. | |AnswerBExp=[[Galactokinase]] catalyzes the conversion of galactose to galactokinase 1 phosphate. The enzyme is already deficient in this patient and it is not directly involved in the synthesis of lactose. | ||
|AnswerC=Galactose 1 phosphate uridyl transferase | |AnswerC=Galactose 1 phosphate uridyl transferase | ||
|AnswerCExp=Galactose 1 phosphate uridyl transferase (GALT) catalyzes the reversible conversion of galactose 1 phosphate to UDP galactose. This enzyme is deficient in patients with classic galactosemia. | |AnswerCExp=Galactose 1 phosphate uridyl transferase ([[GALT]]) catalyzes the reversible conversion of galactose 1 phosphate to UDP galactose. This enzyme is deficient in patients with classic galactosemia. | ||
|AnswerD=UDP galactose epimerase | |AnswerD=UDP galactose epimerase | ||
|AnswerDExp=UDP galactose 4-epimerase (GALE), also known as UDP glucose 4 epimerase, catalyzing the reversible conversion of UDP-galactose to UDP-glucose. GALE tightly binds nicotinamide adenine dinucleotide (NAD+), a co-factor required for catalytic activity. In the absence of an exogenous source of galactose, GALE catalyzes the formation of UDP galactose necessary for the synthesis of lactose. | |AnswerDExp=UDP galactose 4-epimerase ([[GALE]]), also known as UDP glucose 4 epimerase, catalyzing the reversible conversion of UDP-galactose to UDP-glucose. GALE tightly binds nicotinamide adenine dinucleotide (NAD+), a co-factor required for catalytic activity. In the absence of an exogenous source of galactose, GALE catalyzes the formation of UDP galactose necessary for the synthesis of lactose. | ||
|AnswerE=UDP glucose pyrophosphate | |AnswerE=UDP glucose pyrophosphate | ||
|AnswerEExp=UDP glucose pyrophosphate catalyzes the conversion of UDP glucose to glucose 1 phosphate. The enzyme is not directly involved in the synthesis of lactose. | |AnswerEExp=UDP glucose pyrophosphate catalyzes the conversion of UDP glucose to glucose 1 phosphate. The enzyme is not directly involved in the synthesis of [[lactose]]. | ||
|RightAnswer=D | |RightAnswer=D | ||
|Approved=No | |Approved=No | ||
}} | }} | ||
Revision as of 01:41, 16 December 2013
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::A pregnant woman known to have classic galactokinase deficiency is worried she will not be able to breastfeed her baby because she has been on a strict galactose free diet since her birth. The physician comforts her and tells her that she will be having normal breast milk for lactation. The ability of the mammary glands to synthesize milk in the absence of dietary galactose in this patient is due to the activity of which of the following enzymes?]] |
| Answer A | AnswerA::Aldose reductase |
| Answer A Explanation | [[AnswerAExp::Aldose reductase catalyzes the conversion of galactose to galacticol and glucose to sorbitol. It is not involved in the synthesis of galactose or lactose.]] |
| Answer B | AnswerB::Galactokinase |
| Answer B Explanation | [[AnswerBExp::Galactokinase catalyzes the conversion of galactose to galactokinase 1 phosphate. The enzyme is already deficient in this patient and it is not directly involved in the synthesis of lactose.]] |
| Answer C | AnswerC::Galactose 1 phosphate uridyl transferase |
| Answer C Explanation | [[AnswerCExp::Galactose 1 phosphate uridyl transferase (GALT) catalyzes the reversible conversion of galactose 1 phosphate to UDP galactose. This enzyme is deficient in patients with classic galactosemia.]] |
| Answer D | AnswerD::UDP galactose epimerase |
| Answer D Explanation | [[AnswerDExp::UDP galactose 4-epimerase (GALE), also known as UDP glucose 4 epimerase, catalyzing the reversible conversion of UDP-galactose to UDP-glucose. GALE tightly binds nicotinamide adenine dinucleotide (NAD+), a co-factor required for catalytic activity. In the absence of an exogenous source of galactose, GALE catalyzes the formation of UDP galactose necessary for the synthesis of lactose.]] |
| Answer E | AnswerE::UDP glucose pyrophosphate |
| Answer E Explanation | [[AnswerEExp::UDP glucose pyrophosphate catalyzes the conversion of UDP glucose to glucose 1 phosphate. The enzyme is not directly involved in the synthesis of lactose.]] |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::The patient suffers from galactokinase deficiency, a genetic disease of the galactose metabolism. Patients with galactokinase deficiency are required to have a galactose free diet to avoid the accumulation of galacticol. Even in the absence of dietary galactose, the endogenous synthesis of galactose occurs in the body. Galactose is produced in the form of UDP galactose through the activity of the epimerase enzyme on UDP glucose. The synthesis of lactose (milk) in the mammary glands results from the activity of lactose synthase on UDP galactose and glucose.
Learning objective: Even in the absence of dietary galactose, the endogenous synthesis of galactose occurs in the body through the activity of the epimerase enzyme on UDP glucose. Reference: Shcwarz V. Disorders of galactose metabolism. Journal of clinical pathology (1969). |
| Approved | Approved::No |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |