Official Step 1 High Yield Concepts Thread

[Transposony]

Let's discuss our doubts/offer clarifications about mechanisms/concepts for Step 1

ASK ANY QUESTIONS here.

To kick start the thread here is something I didn't know:

1. Penicillin-binding proteins (PBPs) are actually enzymes (transpeptidases & carboxypeptidases) which cross-link peptidoglycan. Penicillins binds to these enzymes and inactivating them thereby preventing cross-linkiing of peptidoglycan.

2. Periplasmic space (Gram -ve) contain proteins which functions in cellular processes (transport, degradation, and motility). One of the enzyme is β-lactamase which degrades penicillins before they get into the cell cytoplasm.
It is also the place where toxins harmful to bacteria e.g. antibiotics are processed, before being pumped out of cells by efflux transporters (mechanism of resistance).

There are three excellent threads which you may find useful:

List of Stereotypes

Complicated Concepts Thread

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[Mr. Mojo Risin]

Oh duh... PCC-induced Vit. C deficiency. I was totally thinking the other way on that one with what vitamin deficiency causes PCC. D'oh!

Great question.

 

[Transposony]

What vitamin(s) would be deficient in a vegan (doesn't eat milk & eggs) v/s a vegetarian (does eat milk & eggs) ?

 

[syoung]

B12

 

[Transposony]

Does human genome normally contains a reverse transcriptase ?

 

[Mr. Mojo Risin]

Does human genome normally contains a reverse transcriptase ?

Telomerase

 

[dfib slim]

Sequelae from an organism that grows on Skirrow agar?

 

[dfib slim]

How could you differentiate between Bernard-Soulier syndrome and von Willibrand disease?

 

[Transposony]

How could you differentiate between Bernard-Soulier syndrome and von Willibrand disease?

Giant platelets.

 

[Transposony]

Sequelae from an organism that grows on Skirrow agar?

Guillain-Barre syndrome

 

[Transposony]

Exception to the rule of Step 1 "never going to court for consent to treatment" ?

 

[dfib slim]

Giant platelets.

What else?

 

[Transposony]

What else?

PTT is usually affected in von Willebrand disease.
Also, ristocetin assay can differentiate.

 

[dfib slim]

PTT is usually affected in von Willebrand disease.
Also, ristocetin assay can differentiate.

Yup, that's what I was getting at. The addition of normal plasma will cause agglutination in a patient with vWD but not BSS.

 

[faisal 2000]

What happen if the mother is Rh+ and the fetus is Rh- Does the same process of attack occur and if not why?

 

[seminoma]

Guillain-Barre syndrome

And reiters.

 

[seminoma]

What happen if the mother is Rh+ and the fetus is Rh- Does the same process of attack occur and if not why?

No attack. Fetus doesn't have antigens for the mom to attack.

 

[seminoma]

During exercises such as heavy weight lifting, does blood flow increase or decrease to the muscle? Why?

 

[dfib slim]

And reiters.

Nazi

 

[seminoma]

Nazi

Wegeners too

 

[faisal 2000]

why there is no development of collateral circulation in pre ductal coaractation ?

 

[seminoma]

why there is no development of collateral circulation in pre ductal coaractation ?

The body is a lazy POS and won't do anymore work than it needs to. The fetus normally circulates deoxygenated O2 to the lower body and therefore it doesn't see a preductal coarctation as a problem. No problem = not gonna do anything to fix it (lazy POS).

In postductal coarctations, development of collateral flow causes an increase in retrograde flow through which artery(ies)?

 

[Phloston]

What vitamin(s) would be deficient in a vegan (doesn't eat milk & eggs) v/s a vegetarian (does eat milk & eggs) ?

Wouldn't pigeonhole this one. Tons of non-vegan vegetarians have low B12, including those I've seen in clinic who have needed B12 injections. I also have a relative who is pescetarian who had to have a B12 injection. Veganism is just on the extreme side of things, which is why a greater % of them will have low B12.

 

[Phloston]

Telomerase

Telomerase was the answer to a question in Kaplan QBank asking for which was an RNA-dependent DNA polymerase.

 

[Transposony]

I can't get my head around this concept.
Since translation is responsible for synthesis of proteins and most enzymes and initiation factors are required for translation are proteins, how were these made to start with?
Is it a chicken or the egg dilemma ?

 

[Transposony]

Does anyone knows how HY is CCA tail of t-RNA ?
It is mentioned is FA but not many details are given.

 

[Mr. Mojo Risin]

I can't get my head around this concept.
Since translation is responsible for synthesis of proteins and most enzymes and initiation factors are required for translation are proteins, how were these made to start with?
Is it a chicken or the egg dilemma ?

We are medical students, not philosophers!

I'll bite... G0?

 

[Mr. Mojo Risin]

Does anyone knows how HY is CCA tail of t-RNA ?
It is mentioned is FA but not many details are given.

Other than it being where the AA is charged, probably not very HY.

 

[dfib slim]

I can't get my head around this concept.
Since translation is responsible for synthesis of proteins and most enzymes and initiation factors are required for translation are proteins, how were these made to start with?
Is it a chicken or the egg dilemma ?

Ribozymes?

 

[dfib slim]

The body is a lazy POS and won't do anymore work than it needs to. The fetus normally circulates deoxygenated O2 to the lower body and therefore it doesn't see a preductal coarctation as a problem. No problem = not gonna do anything to fix it (lazy POS).

In postductal coarctations, development of collateral flow causes an increase in retrograde flow through which artery(ies)?

Intercostal arteries

 

[dfib slim]

During exercises such as heavy weight lifting, does blood flow increase or decrease to the muscle? Why?

During exercise, blood flow increases due to locally produced mediators causing vasodilation but with the prolonged contraction of heavy lifting I'd think the vessels would be compressed and flow would decrease.

 

[stepone2015]

During exercise, blood flow increases due to locally produced mediators causing vasodilation but with the prolonged contraction of heavy lifting I'd think the vessels would be compressed and flow would decrease.

With a reactive hyperemia once contraction ends.

 

[Transposony]

Genetic mutation will most commonly affect which of the following:
1. Spacer DNA
2. Introns
3. Exons
4. 28 subunit of 60S ribosome
5. Elongation factors

 

[Transposony]

During exercise, blood flow increases due to locally produced mediators causing vasodilation but with the prolonged contraction of heavy lifting I'd think the vessels would be compressed and flow would decrease.

I think it's other way around.
Local mediators can't accumulate unless the flow is decreased?

 

[dfib slim]

Genetic mutation will most commonly affect which of the following:
1. Spacer DNA
2. Introns
3. Exons
4. 28 subunit of 60S ribosome
5. Elongation factors

Statistically wouldn't it be spacer DNA because that's what makes up most of the genome?

 

[dfib slim]

I think it's other way around.
Local mediators can't accumulate unless the flow is decreased?

Exercising muscle produces vasodilator metabolites like lactate and adenosine which causes dilation of the arterioles in those areas.

 

[dfib slim]

Cranial nerve defect in Kallmann syndrome?

 

[dfib slim]

Cushing's disease vs Cushing's syndrome?

 

[Transposony]

Exercising muscle produces vasodilator metabolites like lactate and adenosine which causes dilation of the arterioles in those areas.

Muscles contraction compresses blood vessels in the muscles which causes vasodilator metabolites accumulation leading to autoregulation of local arterioles.
Unless the blood flow decreases there will not an accumulation of these metabolites and hence no dilation of the local arterioles.

 

[stepone2015]

Muscles contraction compresses blood vessels in the muscles which causes vasodilator metabolites accumulation leading to autoregulation of local arterioles.
Unless the blood flow decreases there will not an accumulation of these metabolites and hence no dilation of the local arterioles.

As he said, blood flow does decrease because the muscle is contracted blocking flow. During this period of stasis, blood vessels begin to dilate without an increase in flow. Once contraction ends, the area sees hyperemia due to the pent up vasodilation until it can all be washed away.

 

[Transposony]

Mechanism behind ribosomal ditachment from ER during hypoxia?

 

[dfib slim]

Mechanism behind ribosomal ditachment from ER during hypoxia?

Doesn't the swelling cause them to just pop off? The swelling due to the Na+/K+ ATPase shutting down and influx of water.

 

[Transposony]

Once contraction ends, the area sees hyperemia due to the pent up vasodilation until it can all be washed away.

Reactive hyperemia is due to "O2 debt" of the muscle.

 

[Transposony]

Doesn't the swelling cause them to just pop off? The swelling due to the Na+/K+ ATPase shutting down and influx of water.

Protein synthesis requires energy (4 HE-P per AA) and when the source of energy dries up these ribosomes find no incentive to sit on the toilet.

 

[dfib slim]

Protein synthesis requires energy (4 HE-P per AA) and when the source of energy dries up these ribosomes find no incentive to sit on the toilet.

Greedy little guys

 

[Transposony]

What are elongation factors and how do they work in translation?

 

[seminoma]

Intercostal arteries

Which ones?

 

[seminoma]

During exercise, blood flow increases due to locally produced mediators causing vasodilation but with the prolonged contraction of heavy lifting I'd think the vessels would be compressed and flow would decrease.

Yup. During weight lifting blood flow is decreased. During cardio type stuff it is increased.

 

[dfib slim]

Which ones?

The few below the coarctation

 

[faisal 2000]

where/how regulation of Iron Homeostasis occurs

 

[Transposony]

Which ones?

A HY point about coaractation of aorta-The blood flow in the intercostal arteries is reversed below the defect.
Also, for a coarctation that is proximal to the left subclavian, the right subclavian will have it's normal blood supply, so the pulse will be strong, but the left subclavian will not receive it's blood supply, hence the weak pulses.

Some great discussion about coaractation of aorta here