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NBME 21 Answers

nbme21/Block 1/Question#45 (reveal difficulty score)
An 18-year-old man comes to the physician ...
Pyruvate kinase ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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 +11  upvote downvote
submitted by โˆ—basic_pathology(25)
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Key Fact Being Tested: Pyruvate Kinase (PK) is the only enzyme in glycolysis that occurs AFTER the formation of 1,3-BPG

Normally, Glucose -->--> G3P --> 1,3-BPG --> 3-PG -->--> Pyruvate

In this case, 1,3-BPG cannot be converted to 3-PG.

Thus, 1,3-BPG is shunted to 2,3-BPG. This step bypasses ATP production. Since rbc's rely on glycolysis for ATP, this leads to hemolysis"

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unknown001  now what you said its true, this is normally what happens in an RBC, and not as you are trying to say, a pathology. now whats the point of the question. pyruvate kinase deficency leads to accumulation of substrates before this final reaction, and 2,3 BPG happens to be one of them +



 +10  upvote downvote
submitted by โˆ—est88(19)
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Pyruvate Kinase defect leads to decreased ATP leading to rigid RBCs and extra vascular hydrolysis. Increased levels of 2,3-BPG decreases hemoglobin affinity for O2.

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baja_blast  FA 2019 pg 414 +2



 +2  upvote downvote
submitted by โˆ—cantaloupe5(87)
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For this one you just had to know the glycolysis pathway. Stem told you 2,3-BPG is elevated, which is upstream of pyruvate kinase.

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neonem  Right, and that glycolytic enzyme deficiencies lead to hemolytic anemias. +5
toxoplasmabartonella  I just thought the typical presentation of pyruvate kinase deficiency would be hemolytic anemia of the newborn. +4



 +2  upvote downvote
submitted by โˆ—h0odtime(54)
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  • Normocytic Intrinsic Hemolytic Anemia: Reticulocyte >>2.5%
  • PEP --> Pyruvate (last step of Glycolysis) second ATP producing step
  • Mature RBC require pyruvate kinase without it they depend on the anaerobic generation of ATP
  • With insufficient ATP, all active processes in the cell come to a halt. Sodium potassium ATPase pumps are the first to stop: increase intracellular K+, water leaves cell with Na+. Cell Shrinks & dies. Body is deficient in RBC + destroyed by lack of ATP = Hemolytic Anemia
  • Inheritance: AR
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b1ackcoffee  ermm . buddy, stopping NaKATPase causes RISE in intracellular Na, cell SWELLS and dies. +4



 +1  upvote downvote
submitted by โˆ—meryen13(48)
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pt had high indirect bilirubin with high reticulocyte count---> hemolytic anemia. which one in the options is showing hemolytic anemia? pyruvate kinase def.

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