Biochem Questions Thread for Step 1

[MudPhud20XX]

Hi all, again I would like to begin posting biochem questions especially for MS2 who want to review while studying MS2 subjects. Just by doing a couple questions per day I think can make a big change. These are NOT from Uworld, First aid RX, and Kaplan.
Please feel free to add yours.

A 4-year-old boy is brought to the clinic because of a 2-week history of seizures that occur about every 3 days. Medical history is relevant for developmental delay with poor sitting and limited motor movements noticed at 12 months of age. He also has delayed language skills and swallowing difficulty that developed during the past 3 months. His vision and hearing have been deteriorating. Physical examination shows muscle weakness centrally and in all extremities. Fundoscopic examination shows a red spot on the retina. Which of the following is the most likely cause of this boy’s condition?

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[Transposony]

Could rifampin, pza, or inh cause orange tonsils?

No, since rifampin is not stored in macrophages.

 

[Transposony]

An afebrile 50-year-old man with a 30-year history of smoking two packs of cigarettes a day complains of flushing in his face, watery diarrhea, and a 14-kg (30-pound) weight loss over the past 6 months. Physical examination shows an enlarged, nodular liver and a grade 3 pansystolic murmur heard best along the left parasternal border. The murmur increases in intensity on inspiration. Which laboratory study would be most useful in confirming the diagnosis?

5-HIAA in a 24-hour urine collection

 

[Transposony]

A 6-year-old boy has pitting edema, abdominal pain, proteinuria, and hyperlipidemia. A kidney biopsy specimen indicates minimal change disease. The figure shows a normal electrophoretic pattern of albumin (Alb) and other plasma proteins. It also shows five abnormal patterns, each labeled with a capital letter. Which of the patterns is most likely to be seen in a patient with these symptoms?

Only two answers are possible in this- B or C since only these two are showing decreased albumin.

B is also showing an increase in gamma globulin which is unlikely to happen in MCD.
Answer is C since it is also showing an elevated alpha-2 which is typical of nephrotic syndrome.

Serum protein electrophoresis

How to Read the Electrophoretic Pattern of Serum Protein

 

[MudPhud20XX]

A 20-year-old develops diffuse muscle tenderness and red-colored urine shortly after finishing a 20-mile run on a hot, humid day. Laboratory tests show a markedly elevated serum creatine kinase and a positive urine dipstick for blood. Red blood cells are not present in the urine sediment examination. What is a characteristic feature of the pigment in the urine?

 

[MudPhud20XX]

A 26-year-old man who has been homeless for 6 months is unconscious on arrival at the emergency department. His blood is positive for ketones and has a pH of 7.3. He is started on intravenous glucose and given a high carbohydrate diet after regaining consciousness. This treatment would most likely increase the activity of which enzyme?

A. citrate synthase
B. lipoprotein lipase

 

[MudPhud20XX]

During a cold spell, an elderly man and woman are found in their home short of breath and complaining of headaches and flulike symptoms. They were using a wood stove to keep themselves warm. They are taken to a clinic, where examination shows that they have cherry-red flushing of the skin and mucous membranes. The most likely cause of the clinical manifestations is exposure to a substance that acts as a site-specific inhibitor of electron transport. In the accompanying figure, which complex is inhibited by this substance?

 

[Transposony]

During a cold spell, an elderly man and woman are found in their home short of breath and complaining of headaches and flulike symptoms. They were using a wood stove to keep themselves warm. They are taken to a clinic, where examination shows that they have cherry-red flushing of the skin and mucous membranes. The most likely cause of the clinical manifestations is exposure to a substance that acts as a site-specific inhibitor of electron transport. In the accompanying figure, which complex is inhibited by this substance?

Complex IV

 

[Transposony]

A 26-year-old man who has been homeless for 6 months is unconscious on arrival at the emergency department. His blood is positive for ketones and has a pH of 7.3. He is started on intravenous glucose and given a high carbohydrate diet after regaining consciousness. This treatment would most likely increase the activity of which enzyme?

A. citrate synthase
B. lipoprotein lipase

A. citrate synthase

 

[Transposony]

A 20-year-old develops diffuse muscle tenderness and red-colored urine shortly after finishing a 20-mile run on a hot, humid day. Laboratory tests show a markedly elevated serum creatine kinase and a positive urine dipstick for blood. Red blood cells are not present in the urine sediment examination. What is a characteristic feature of the pigment in the urine?

Myoglobinuria

 

[MudPhud20XX]

Complex IV

very good. complex 4 is inhibited by CO or cyanide

 

[MudPhud20XX]

A. citrate synthase

this is a tricky one. the answer is lipoprotein lipase that is upregulated by insulin

 

[MudPhud20XX]

Myoglobinuria

correct, rabdo.

 

[MudPhud20XX]

Investigators are studying the regulation of glycolytic pathway enzymes in a culture of hepatocytes. After citrate is added to the culture, a substrate of which of the following enzyme-catalyzed reactions accumulates in the hepatocytes?

 

[dfib slim]

Investigators are studying the regulation of glycolytic pathway enzymes in a culture of hepatocytes. After citrate is added to the culture, a substrate of which of the following enzyme-catalyzed reactions accumulates in the hepatocytes?

PK

 

[aspiringmd1015]

A 26-year-old man who has been homeless for 6 months is unconscious on arrival at the emergency department. His blood is positive for ketones and has a pH of 7.3. He is started on intravenous glucose and given a high carbohydrate diet after regaining consciousness. This treatment would most likely increase the activity of which enzyme?

A. citrate synthase
B. lipoprotein lipase

glucose stimulates insulin, insulin makes f26bp in the liver via pfk2, so glycolysis is continuing, mostly for biosynthesis of cholesterol and fatty acids, and insulin increases lipase to break down these arriving fatty acids once the liver packages them, for eventual storage within the fat.

 

[Transposony]

this is a tricky one. the answer is lipoprotein lipase that is upregulated by insulin

Can't believe I fell for that one.
Time to review Biochem again.

 

[aspiringmd1015]

regarding the ETC, why with the uncouplers, do you get increased 0xygen consumption and increased oxidation of nadh?

 

[aspiringmd1015]

?

 

[dfib slim]

?

Because you need to pump extra hydrogen ions into the intermembrane space to compensate for the leakage?

 

[aspiringmd1015]

ok so that contributes to increased nadh oxidation, but what about increased 0xygen consumption?

 

[dfib slim]

The oxidation of NADH through the ETC and pumping of H+ depends on the terminal electron acceptor oxygen. When you have to pump more H+, you need increased oxygen to consume all the extra electrons being passed down the chain.

 

[aspiringmd1015]

okay, but uncouplers don't allow the formation of the proton gradient in the first place right, so if the proton gradient isn't forming, oxygen is still accepting the electrons?

 

[dfib slim]

I thought the uncouplers decreased the proton gradient based upon how much chemical is present, not preventing the formation entirely.

 

[aspiringmd1015]

idk, someone help!

 

[aspiringmd1015]

the ETC never made complete sense to me, guess my lack of chemistry concepts would account for that

 

[Mr. Mojo Risin]

The oxidation of NADH through the ETC and pumping of H+ depends on the terminal electron acceptor oxygen. When you have to pump more H+, you need increased oxygen to consume all the extra electrons being passed down the chain.

I think you have the right idea here. The uncouplers I think are trapping the H+ that would be going through the channel to make ATP thereby abolishing the proton gradient, but the other complexes are still pumping H+ out into the IMM.

 

[aspiringmd1015]

from my understanding i thought the uncouplers prematurely made the protons go into the mitochondrial matrix as a site before the fo/f1 channel, thus not being able to make atp as they have to go through that channel to encounter atp syynthase to form atp.

 

[Mr. Mojo Risin]

from my understanding i thought the uncouplers prematurely made the protons go into the mitochondrial matrix as a site before the fo/f1 channel, thus not being able to make atp as they have to go through that channel to encounter atp syynthase to form atp.

?

 

[dfib slim]

?

Lol, I think he means for example the 2,4 DNP travels into the intermembrane space, picks up H ions, then drops them back of in the matrix so they don't have a chance to go through the F1/F0 aka the ATP synthase.

 

[StIGMA]

Uncouplers prevent the ETC from functioning as stated above. The cell still needs energy and you have excess NADH that the cell cannot turn to ATP via the ETC.

Reduced (energetic) NADH must still be turned over to NAD (oxidized eg: replenished to NAD) to allow glycolysis to occur for alternate ATP production. The mitochondria uses oxygen in complex IV to quench the H+, allowing complex 1 to continue to oxidize NADH to NAD to allow glycolysis to continue. Oxygen is effectively competing with the uncoupler to restore the pH gradient and in doing so regenerating NAD.

(or so im postulating, dont have my textbook with me)

 

[syma]

Uncouplers change the permeability of the membrane to allow hydrogen through without having to use the ATP synthetase making thing. (Forgot the name)