Prep4USMLE Forum » USMLE Step 1 Forum » Biochemistry Forum |   please explain the answer

Author	8 Posts
nadiabarati	03/13/06 - 06:56 PM             #1 A 39-year-old man consumes a carbohydrate-rich diet. Which of the following best characterizes the enzyme that will be increased in this patient? Click on the circle next to your answer choice A. Catalyzes the conversion of glucose to glucose-6-phosphate in peripheral tissues B. Catalyzes the rate-limiting step in glycolysis C. Characterized by a high affinity (low Km) for glucose D. Functions only when the glucose concentration in hepatocytes is relatively high E. Inhibited by glucose-6-phosphate
mazinger Forum Guru Topics: 46 Posts: 916	03/13/06 - 07:01 PM             #2 I would go for d.. why? because if you have a high carb diet, means you have high insulin levels, which in fact induces its transcription, its glucokinase.. It has a lower affinity for glucose than hexokinase (higher km), it only phosphorylates glucose when intracell levels are high... ___________________ Ultraseven X
nadiabarati	03/13/06 - 08:28 PM             #3 thanks mazinger, but I'm just wondering that also hexokinase in peripheral tissues starts glycolysis. why do you just focus on glycolysis by glucokinase in liver? Why is E wrong? glucose 6p inhibits both lucokinase and hexokinase. Please help me to get the point
mazinger Forum Guru Topics: 46 Posts: 916	03/13/06 - 08:37 PM             #4 Well, now you made me hesitate.... from my point of view this is what's happening, insulin is released second to high blood glucose levels.. Insulin induces glucokinase only.. Hexokinase is expressed constitutively in all tissues, specially in those where glucose uptake is totally independent of insulin. Yes its true, g6p inhibits both gk and hk, but hk is normal in this individual.. The only enzyme I can think of that is over expressed is gk.. What's the answer by the way? Did I get it right? ___________________ Ultraseven X
nadiabarati	03/13/06 - 08:45 PM             #5 yes you are right. the answer is D. Please let me know what source you used for biochemistry? I think my source wasn't enough.
mazinger Forum Guru Topics: 46 Posts: 916	03/13/06 - 11:25 PM             #6 Well, it was kaplan biochem and lionel raymond... this guy is amazing... Think biochem is one of my strongest subjects, Im scoring over 90 on this particular subject... Probably biochem is not heavily tested in step 1, but its so important for understanding other material... SO IMPORTANT, specially pathology.. It has lots of overlap bet, immuno, microbio, physio.. and pharm of course.. Try to get those sources and you will be just fine. ___________________ Ultraseven X
thatsme Forum Newbie Topics: 4 Posts: 22	03/14/06 - 05:48 PM             #7 D is also mine. For nadiabarati , please do a lot of test from BSS CD. i SAW ONE QUESTION LIKE THIS ONE FEW DAYS AGO. THE BIOCHEMISTRY QUESTIONS ARE GOOD FOR LEARNING MANY CONCEPTS
nadiabarati	03/15/06 - 04:51 PM             #8 How can I get this CD, dear thatsme??

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