Official Step 1 HY Biochem Concepts & Discussion Thread

[Mr. Mojo Risin]

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Feel free to use this thread to discuss HY Biochem concepts. Good luck to everyone!

Links to the other HY subject threads:

Cardiology: http://forums.studentdoctor.net/thr...ardiology-concepts-discussion-thread.1115425/

Endocrinology: http://forums.studentdoctor.net/thr...crinology-concepts-discussion-thread.1115426/

Gastroenterology: http://forums.studentdoctor.net/thr...nterology-concepts-discussion-thread.1115427/

Hematology/Oncology: http://forums.studentdoctor.net/thr...-oncology-concepts-discussion-thread.1115428/

Immunology: http://forums.studentdoctor.net/thr...mmunology-concepts-discussion-thread.1115423/

Microbiology: http://forums.studentdoctor.net/thr...-microbio-concepts-discussion-thread.1115422/

MSK/Skin/Connective Tissue: http://forums.studentdoctor.net/thr...ve-tissue-concepts-discussion-thread.1115430/

Neurology: http://forums.studentdoctor.net/thr...neurology-concepts-discussion-thread.1115431/

Psychiatry: http://forums.studentdoctor.net/thr...sychiatry-concepts-discussion-thread.1115432/

Renal: http://forums.studentdoctor.net/threads/official-step-1-hy-renal-concepts-discussion-thread.1115433/

Reproductive: http://forums.studentdoctor.net/thr...roductive-concepts-discussion-thread.1115434/

Respiratory: http://forums.studentdoctor.net/thr...spiratory-concepts-discussion-thread.1115435/

 

[MudPhud20XX]

Cool, so I'll post my first question

A 30 yr old secretary is unable to have lunch or dinner during a busy grant renewal time at a research lab. Which of the following enzymes helps maintain blood glucose levels from its storage from in the liver?

A. alpha 1, 4 transferase
B. Debranching enzyme
C. Glucose 6 phosphatase
D. Glucose 6 phosphate dehydrogenase
E. Glycogen phosphorylase

So the answer is C, but why not B or C which is the same enzyme?

Since both glucose 6 phosphatase and debranching (glycogen phosphorylase) are involved in converting glycogen to glucose right?

 

[dfib slim]

E is also involved in converting glycogen to glucose but both E and B aren't the last enzyme reaction before the glucose leaves the liver.

 

[dfib slim]

A mother brings her newborn into the clinic for evaluation. Shortly after starting breast feeding the child developed symptoms of vomiting, yellowing of the skin, and a swollen liver. Which condition is the child most likely suffering from?

A. Lactose intolerance

B. Classic galactosemia

C. Fructose intolerance

D. Galactokinase deficiency

 

[Mr. Mojo Risin]

A mother brings her newborn into the clinic for evaluation. Shortly after starting breast feeding the child developed symptoms of vomiting, yellowing of the skin, and a swollen liver. Which condition is the child most likely suffering from?

A. Lactose intolerance

B. Classic galactosemia

C. Fructose intolerance

D. Galactokinase deficiency

classic galactosemia. A and D would present with more mild symptoms, with D being more likely if it was a kid with delayed development of social smile and inability to track objects due to galactitol-induced cataracts, without the more serious liver pathology seen in classic galactosemia (jaundice, hepatomegaly).

 

[aspiringdoc09]

In gluconeogenesis, does pyruvate carboxylase convert pyruvate to both oxaloacetate (OAA) and phosphoenolpyruvate (PEP) or does it only convert it to OAA while PEP carboxykinase converts OAA to PEP? Kaplan makes it seem like the former and then they say PEP carboxykinase also converts OAA to PEP. Thanks.

 

[dfib slim]

In gluconeogenesis, does pyruvate carboxylase convert pyruvate to both oxaloacetate (OAA) and phosphoenolpyruvate (PEP) or does it only convert it to OAA while PEP carboxykinase converts OAA to PEP? Kaplan makes it seem like the former and then they say PEP carboxykinase also converts OAA to PEP. Thanks.

Pyruvate carboxylase is in the mitochondria and converts pyruvate to OAA. OAA needs to leave the mitochondria via the malate/asparate shuttle. Once in the cytosol, PEP carboxykinase can convert OAA to PEP.

 

[aspiringdoc09]

Pyruvate carboxylase is in the mitochondria and converts pyruvate to OAA. OAA needs to leave the mitochondria via the malate/asparate shuttle. Once in the cytosol, PEP carboxykinase can convert OAA to PEP.

Thanks for the clarification

 

[seminoma]

Misfolded proteins (as in AAT deficiency or CF) get trapped in which organelle?

 

[dfib slim]

Misfolded proteins (as in AAT deficiency or CF) get trapped in which organelle?

ER

 

[dfib slim]

Organelle involved in Refsum disease?

 

[seminoma]

Organelle involved in Refsum disease?

Peroxisome! Haven't seen Refsum since MS1 biochem, wow.

 

[dfib slim]

Peroxisome! Haven't seen Refsum since MS1 biochem, wow.

What about dysfunctional organelle in progeria?

 

[seminoma]

What about dysfunctional organelle in progeria?

Never heard of it, but I just read about it on wiki and it's kind of cool. I'll let someone else answer without cheating.

 

[dfib slim]

Never heard of it, but I just read about it on wiki and it's kind of cool. I'll let someone else answer without cheating.

Check out MC progeria on YouTube

 

[Mr. Mojo Risin]

I have written down that it involves nuclear lamins, the intermediate filaments of the nucleus, so that's my answer.

 

[dfib slim]

I have written down that it involves nuclear lamins, the intermediate filaments of the nucleus, so that's my answer.

Yup

 

[aspiringdoc09]

Based on these data, which of the following is the probability that III-2 is a carrier?

A) 100%
B) 50%
C) 33%
D) 25%
E) 0%

 

[dfib slim]

100% right?

 

[aspiringdoc09]

No

 

[guspilgrim]

View attachment 189744

Based on these data, which of the following is the probability that III-2 is a carrier?

A) 100%
B) 50%
C) 33%
D) 25%
E) 0%

Seems like it should be 100% based on the gene data (she appears to have the bad gene) - what are we missing?

If they didn't give you the gene data and just asked you to figure it out - 25%

50% chance the mother is a carrier and 50% chance the daughter gets the bad X. Probability daughter will be a carrier is 50% x 50%

 

[aspiringdoc09]

Seems like it should be 100% based on the gene data (she appears to have the bad gene) - what are we missing?

If they didn't give you the gene data and just asked you to figure it out - 25%

50% chance the mother is a carrier and 50% chance the daughter gets the bad X. Probability daughter will be a carrier is 50% x 50%

Honestly, I am still confused by this question. I thought it should have been 25% too, but they said it was E when you combined the pedigree and southern blot data. Here is their explanation:

 

[dfib slim]

Honestly, I am still confused by this question. I thought it should have been 25% too, but they said it was E when you combined the pedigree and southern blot data. Here is their explanation:

View attachment 189759

I see what they are getting at. 25% if they didn't give you the blot. The blot shows only 2 different haplotypes for the gene in question, top band and bottom band, that contain HindIII polymorphisms. But since III-3 and III-4 are unaffected and each inherited a different copy of the gene, II-5 would not be a carrier.

All the bands in the blot have the HindIII polymorphism located in a different part of the restriction enzyme recognition site and doesn't result in disease.

 

[seminoma]

That's a pretty tough question.. I probably would just guess and move on if it showed up on the real exam. Here's how I got to 0% though, if it helps.

I think we can all agree that based on the pedigree alone II-5 has a 50% chance of being a carrier and III-2 has a 25% chance of being a carrier. Since the question says it's x-linked we know that II-4 has a normal gene. Now looking at the blot, II-5 has given each of her sons a different allele. Since both of her sons are unaffected we know that II-5 is not a carrier. If II-5 is not a carrier and II-4 is unaffected, then III-2 cannot be a carrier.

 

[shibby1111]

Regarding von Gierke disease, a glucose-6-phosphatase defciency, characterized by severe hypoglycemia, many other things, and lactic acidosis. I don't understand how this causes lactic acidosis. Please help. thanks.

 

[Mr. Mojo Risin]

Regarding von Gierke disease, a glucose-6-phosphatase defciency, characterized by severe hypoglycemia, many other things, and lactic acidosis. I don't understand how this causes lactic acidosis. Please help. thanks.

Increased G6P --> pyruvate --> lactate via LDH and ALT.

 

[dfib slim]

Regarding von Gierke disease, a glucose-6-phosphatase defciency, characterized by severe hypoglycemia, many other things, and lactic acidosis. I don't understand how this causes lactic acidosis. Please help. thanks.

That enzyme is common to both glycogenolysis and gluconeogenesis pathways. Inhibition of gluconeogenesis will lead to lactic acidosis.

 

[pathologyDO]

So I basically suck at biochem bcuz our osteopathic curriculum doesn't teach it as heavily as needed for USMLE. I have this idea that if I print off some super high yield pathways and stick em on my wall, I will periodically glance over them and maybe that will help with long term retention. Anyone have any good pathway images I could use? Even ideas of which pathways would be most HY would help

 

[aspiringmd1015]

FA

 

[pathologyDO]

FA

Why thanks, it must have slipped my mind that the #1 resource for all med students would have some biochem images in it 🙄

 

[Slade009]

Why thanks, it must have slipped my mind that the #1 resource for all med students would have some biochem images in it 🙄

Personally my school lacked teaching me Biochemistry properly (along with other subjects) so I started from scratch. Personally I learned 1/2 my Biochemistry from DIT (Doctors in Training) and the other 1/2 from repetition (seeing them over and over again) and questions (Qbanks and different exam sources). Although some may argue my technique might not be efficient, but it worked for me. DIT basically goes over FA + their own additional points in fairly easy understanding and explanations that clinically relate for the most part.

I think you should do the Print and Tape on the wall idea and you should do a couple of Biochemistry questions a day to familiarize yourself better.
And as to your which pathways would be high yield, to tell you the truth the Step 1 is fair game and they could include any/all pathways so it's best you do and learn them all.

My wise words: Mentally prepare for the worst and then expect the best. Meaning if you are already anticipating anything and all things bad in their worst case scenario then everything else to come isn't a surprise and you can expect the best without worrying as much. Life lesson also 🙂

 

[Slade009]

I have a dilemma and I wonder if it's the same with you guys as well. Every time I want to post a question just before posting I think..hmm that's probably too easy for them...lol and then ERASE. Then I type in another question and think...hmm no it has that buzzword/side effect/obvious presentation/obvious result.....ERASE. lol. This goes for all the high yield threads. I feel like we're all trying to in a sense trick each other (well frankly I'm looking for new concepts to learn and to teach) so sometimes I don't end up posting questions thinking they're too easy. But what might be easy to me might be hard for someone else and vice versa.

 

[pathologyDO]

I have a dilemma and I wonder if it's the same with you guys as well. Every time I want to post a question just before posting I think..hmm that's probably too easy for them...lol and then ERASE. Then I type in another question and think...hmm no it has that buzzword/side effect/obvious presentation/obvious result.....ERASE. lol. This goes for all the high yield threads. I feel like we're all trying to in a sense trick each other (well frankly I'm looking for new concepts to learn and to teach) so sometimes I don't end up posting questions thinking they're too easy. But what might be easy to me might be hard for someone else and vice versa.

Thank you for your advice and also, don't worry about whether you think the Q is easy or not. I feel the same when posting a Q... I feel like SDN has more top notch students and if I post something easy people might think its useless... But in general I think that what you might find to be a gimme question with easy buzzwords might be a topic that someone else hasn't even covered yet and will have no idea how to answer, so post away!!

 

[theTruth_97]

not sure where to put this question since there's no separate pharm section I believe.....but i was wondering for Cytochrom P450 system First Aid says that substrates it acts on is Theophylline, Warfarin, OCPs and anti-epileptics. Are there any other high yield ones that anyone can think of?

thank you!

 

[Slade009]

not sure where to put this question since there's no separate pharm section I believe.....but i was wondering for Cytochrom P450 system First Aid says that substrates it acts on is Theophylline, Warfarin, OCPs and anti-epileptics. Are there any other high yield ones that anyone can think of?

thank you!

As far as I know those are the only High Yield ones to my knowledge.

 

[seminoma]

not sure where to put this question since there's no separate pharm section I believe.....but i was wondering for Cytochrom P450 system First Aid says that substrates it acts on is Theophylline, Warfarin, OCPs and anti-epileptics. Are there any other high yield ones that anyone can think of?

thank you!

Statins