Biochemistry usmle step 1 2023 questions and answers

1. Determine the number of ATP molecules, which are formed in Krebs cycle at the conversion of isocitric acid to fumaric acid (I) and to succinyl CoA (II) respectively: A) I -7,0; II - 5,5 B) I - 5; II - 3,5 C) I - 6,5; II - 4,5 D) I - 7,5; II - 5 E) I - 7; II - 3 2. In which stages of citric acid cycle is CO2 formed? 1) Izocitrate - α-Ketoglutarate 2) Succinate - Fumarate 3) α-Ketoglutarate -Succinil-CoA 4) Fumarate – Malate 5) Malate –Oxaloacetate A) 1,3 B) 2,4 C) 1,4 D) 3,4 E) 4,5 3. Choose coenzymes involved in the process of oxydative decarboxylation of pyruvate. A) PALF, THFA, THP, NAD + , FAD B) THFA, TPP, FAD, LA, NAD + C) TPF, FAD, HS-CoA, NAD + , LA D) NADP, FAD, LA, TPF, NAD + E) TPF, NAD + , HS-CoA, PALF, FAD 4. Choose the line of substances used as source of pyruvate A) glycerol, lactic acid, alanine B) glycerin, glucose, PALF C) FAD, fatty acids, oxaloacetate D) HS-CoA, glutamine, leucine E) fatty acid, isocitric acid, acetyl-CoA 5. In which reaction is energy-rich substance produced? A) oxidative decarboxylation of α-ketoglutaric acid B) isomerization of citrate C) the hydration of fumaric acid D) pyruvate carboxylation E) the condensation of oxaloacetate with acetyl-CoA 6. Choose the right sequence of substances formed in the citric acid cycle. 1) α-Ketoglutaric acid 2) Citric acid 3) Malic acid 4) Isocitric acid