Official DAT Destroyer Q&A Thread

[densaugeo]

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Hi guys, since I'm currently going through the DAT Destroyer and I'm sure many of you guys are as well I felt this thread would be helpful. I usually have various questions while going through Destroyer regarding why a certain answer choice is correct or other times I am in need of a more detailed explanation.

Instead of making multiple threads each time we have questions, I thought we could just post them here and anyone can chime in with an explanation or further clarification.

Please don't post entire questions as that would be a violation of copyright. You can ask specific questions regarding a particular problem in the Destroyers.

Hopefully others find this a useful thread. Thanks!

 

[cacajuate]

Prokaryotes do generate ATP with Krebs cycle too except unlike euk. it takes place in the cytosol NOT the cell membrane (prokaryotes use the cell membrane as the electron transport chain).

Looks like you are right. I just learned something

 

[510586]

Dont quote me on this, you'll need to look it up but I believe energy is wasted moving the molecules into mito. ask @FeralisExtremum, I know he knows

Yea I knew they wasted energy moving into mito. @StudentDoc1234 is correct I think. Just odd that destroyer stated that red blood cells couldn't do it because they lacked a mitochondria when that's how prokaryotes do it. Didn't look like the best explanation. Maybe someone from destroyer can come clear it up when they see this.

 

[m145491]

For number 3 Ochem 2015, I understand the answer and why it is the answer, but just out of curiosity, if the question asked for the conjugate acid instead of the conjugate base, what would happen then? Would CH3 gain a hydrogen in that case?

 

[DAT Destroyer]

For number 3 Ochem 2015, I understand the answer and why it is the answer, but just out of curiosity, if the question asked for the conjugate acid instead of the conjugate base, what would happen then? Would CH3 gain a hydrogen in that case?

No. Look for that atom that would want to gain an H......in other words,,,the most basic atom.

It would clearly be the Nitrogen !!!!

Thus the conjugate acid would have a protonated NH3 group.

Hope this helps

Dr. Romano

 

[DAT Destroyer]

Yea I knew they wasted energy moving into mito. @StudentDoc1234 is correct I think. Just odd that destroyer stated that red blood cells couldn't do it because they lacked a mitochondria when that's how prokaryotes do it. Didn't look like the best explanation. Maybe someone from destroyer can come clear it up when they see this.

I am not sure of the confusion? Red blood cells do glycolysis. They cannot do TCA cycle. Most prokaryotes function the same. Some have TCA cycle, but that is not the question asked.

 

[510586]

I am not sure of the confusion? Red blood cells do glycolysis. They cannot do TCA cycle. Most prokaryotes function the same. Some have TCA cycle, but that is not the question asked.

I am not sure of the confusion? Red blood cells do glycolysis. They cannot do TCA cycle. Most prokaryotes function the same. Some have TCA cycle, but that is not the question asked.

Sorry it was just the explanation in the back of the book said RBC lacks mitochondria, thus there is no TCA cycle. I was just wondering why prokaryotes use TCA cycle when they lack mitochondria as well. Does lacking mitochondria have any indication of there being a TCA cycle or not?

 

[DAT Destroyer]

Sorry it was just the explanation in the back of the book said RBC lacks mitochondria, thus there is no TCA cycle. I was just wondering why prokaryotes use TCA cycle when they lack mitochondria as well. Does lacking mitochondria have any indication of there being a TCA cycle or not?

Yes. Usually TCA cycle occurs in Mitochondria. The reference was made to prokaryotes, because most of them rely on Glycolysis, just like red blood cells.

 

[510586]

Yes. Usually TCA cycle occurs in Mitochondria. The reference was made to prokaryotes, because most of them rely on Glycolysis, just like red blood cells.

So their glycolysis is able to make the same amount of ATP (or a bit more) as eukaryotes' glycolysis+kreb?

 

[510586]

On 177 of the ochem 2015 destroyer, is LiAlH4 , E2O over H2O not a reducing agent? Sorry ignore this question I misread it.

 

[DAT Destroyer]

So their glycolysis is able to make the same amount of ATP (or a bit more) as eukaryotes' glycolysis+kreb?

No. Glycolysis only makes 2 ATP.

 

[510586]

No. Glycolysis only makes 2 ATP.

Just double checked feralis notes. It seems that they just do their respiration in cell membrane. I guess they have their own kind of process that isn't Krebs that we don't need to know for DAT then

 

[whitepapertree]

.

 

[510586]

Well you should know that the prokaryotes do have a TCA cycle that occurs in the cytosol and their electron transport chain, instead of being the mitochondrial inner membrane, is their actual plasma membrane. Prokaryotes can make 38 ATP while Eukaryotes can make 36 ATP coming from one glucose molecule. It costs 1 ATP per pyruvate to move it from the cytosol to the matrix of the mitochondria

I understand. However, I saw the explanation of no TCA in RBC was because they had no mitochondria. I didn't know if it applied to prokaryotes who also have no mitochondria. It's more so the reasoning that tripped me up a bit. also when I asked or go man about if lack of mitochondria indicates if it has a TCA cycle or not, he said yes. Might ask ferali to clear it up..

 

[510586]

I think things are being interpreted differently differently. It isn't a big deal just the answer to the destroyer seemed to imply that the reason rbc couldn't do Krebs was the lack of their mitochondria. You are now saying it occurs in the cytosol which I'm not denying. I'm trying to get a definite reasoning for why red blood cells don't do Krebs when prokaryotes that lack mitochondria as well can (as you stated)

Well you should know that the prokaryotes do have a TCA cycle that occurs in the cytosol and their electron transport chain, instead of being the mitochondrial inner membrane, is their actual plasma membrane. Prokaryotes can make 38 ATP while Eukaryotes can make 36 ATP coming from one glucose molecule. It costs 1 ATP per pyruvate to move it from the cytosol to the matrix of the mitochondria

)

 

[510586]

http://forums.studentdoctor.net/thr...le-and-etc-take-place-in-prokaryotes.1050948/ this cleared it up you were correct. Guess RBC just don't do Krebs for another reason. Sorry for splitting hairs I'm just using destroyer answers to learn as much as possible so if there is any ounce of gray area I try to clear it up. Thank you for your help everyone!

 

[DAT Destroyer]

Just double checked feralis notes. It seems that they just do their respiration in cell membrane. I guess they have their own kind of process that isn't Krebs that we don't need to know for DAT then

Are you talking about Prokaryotes?

 

[510586]

Are you talking about Prokaryotes?

Yes. Now I know they do both Krebs and ETC in cell membrane

 

[510586]

Dont quote me on this, you'll need to look it up but I believe energy is wasted moving the molecules into mito. ask @FeralisExtremum, I know he knows

Yes that is true I knew that. Thanks

 

[510586]

One of the true statements in destroyer was that prolactin is a hormone that stimulates milk secretion in animals. According to Ferali's notes, oxytocin does that(excreting milk) not prolactin (milk production). Can someone confirm which is correct? Feralis says he has looked at various sources and double checked to make sure it was correct.

 

[whitepapertree]

.

 

[510586]

Oxytocin is more known for uterine contractions rather than the milk-related effect, thus if there is a milk question go with Prolactin.

Even if it is specifically about excretion? Seems risky. Even cliff says oxytocin is for secretion of milk or release of it

 

[DAT Destroyer]

Even if it is specifically about excretion? Seems risky. Even cliff says oxytocin is for secretion of milk or release of it

There is new evidence that Prolactin maybe involved in milk production and secretion. Oxytocin is known to stimulate milk secretion and uterine contraction. Most likely scenario that Prolactin and oxytocin are acting in concert to produce and secrete milk after birth.

http://www.ncbi.nlm.nih.gov/pubmed/8070355

 

[510586]

There is new evidence that Prolactin maybe involved in milk production and secretion. Oxytocin is known to stimulate milk secretion and uterine contraction. Most likely scenario that Prolactin and oxytocin are acting in concert to produce and secrete milk after birth.

http://www.ncbi.nlm.nih.gov/pubmed/8070355

Guess on the DAT we use the new info? Or stick to cliff definition?

 

[510586]

Can someone explain 334 of the bio destroyer 2015? How come q =/= .0004? Isn't the frequency for the allele 1 in 2500? I thought the allele was the lower case letter (like q). So the heterozygous would be 2(p)(q)?

 

[DAT Destroyer]

Can someone explain 334 of the bio destroyer 2015? How come q =/= .0004? Isn't the frequency for the allele 1 in 2500? I thought the allele was the lower case letter (like q). So the heterozygous would be 2(p)(q)?

1 in 2500 represents the recessive allele frequency IN THE POPULATION...this is the q2 term right ? solving for q gives us 0.02......the heterozygote in the population is 2pq......or about 4%.

Hope this helps. Make sure you are clear on the difference between q and q2....

Dr. Romano

 

[510586]

1 in 2500 represents the recessive allele frequency IN THE POPULATION...this is the q2 term right ? solving for q gives us 0.02......the heterozygote in the population is 2pq......or about 4%.

Hope this helps. Make sure you are clear on the difference between q and q2....

Dr. Romano

So recessive allele frequency is the same thing as saying the recessive phenotype? Khan academy said that lower case q is the frequency of the recessive allele. Cliff says lower case p and q represent the allele frequencies as well. Does "in the population" always assume the p^2+2pq +q^2 equation? Every source I've seen has stated that p and q are the allele frequencies that is the source of the confusion. I have gotten every other genetics problem correct using that working definition.
http://www.stat.washington.edu/thompson/Genetics/3.1_population.html they treated allele frequency in population as q here as well.

 

[Bropofol*]

Hello,

For orgo chem #49, in the 2015 Destroyer, after the epoxide forms and the nucleophile 🙂0H5C2) attacks the most substituted carbon (since under acidic conditions and most carbocation-like, wouldn't the nucleophile attack the secondary side b/c the top carbon although more substituted, already has 4 bonds (making it quaternary not tertiatary)? Or it is because under acidic condtitons, the epoxide assumes a partial bond to the carbon, in the same manner that a mercuranium or bromonium ion does?

Thanks in advance!

 

[Bropofol*]

Hello,

For orgo chem #49, in the 2015 Destroyer, after the epoxide forms and the nucleophile 🙂0H5C2) attacks the most substituted carbon (since under acidic conditions and most carbocation-like, wouldn't the nucleophile attack the secondary side b/c the top carbon although more substituted, already has 4 bonds (making it quaternary not tertiatary)? Or it is because under acidic condtitons, the epoxide assumes a partial bond to the carbon, in the same manner that a mercuranium or bromonium ion does?

Thanks in advance!

i wanted to indicate the smiley face was meant to be a lone pair and an open parentheses (as fun as orgo reactions are LOL

 

[DAT Destroyer]

i wanted to indicate the smiley face was meant to be a lone pair and an open parentheses (as fun as orgo reactions are LOL

This is a great question, and virtually every organic chemistry teacher is asked this.

I have attacked the tertiary carbon......the bonds making up the epoxide are NOT equal in strength !!! We do not see a true carbocation.....but as the bond begins to break, we begin to see a " carbocation-like " intermediate.....not seen if we broke the less substituted bond. The bond at the more substituted carbon is weaker...quite a bit weaker..... It is NOT a true SN1 reaction....but reasonably close. Next comes the nucleophilic attack. If in base,,,,we would attack the less substituted carbon, and the argument is steric. I hope this helps.

If you need need further clarity on this......there is a great text by Marc Loudon of Purdue Univesity.

Feel free to ask away if you want more details here. I have lectured all morning long to my DAT students in Organic Chemistry....and would be delighted to help the SDN community

Dr J

 

[universalforceps]

For the 2015 Organic Chemistry Odyssey, I had a quick question regarding Nucleophiles in polar aprotic solvents. From watching Chad, nucleophile strength increases as you go to the left on the periodic table (less electronegative) and for aprotic solvents, as you go up the periodic table. On question #41, why would the SH- nucleophile be the stronger nucleophile rather than the OH- nucleophile in DMF? Isn't DMF an aprotic solvent, so OH would be the stronger nucleophile? Any help would be appreciated!

 

[DAT Destroyer]

For the 2015 Organic Chemistry Odyssey, I had a quick question regarding Nucleophiles in polar aprotic solvents. From watching Chad, nucleophile strength increases as you go to the left on the periodic table (less electronegative) and for aprotic solvents, as you go up the periodic table. On question #41, why would the SH- nucleophile be the stronger nucleophile rather than the OH- nucleophile in DMF? Isn't DMF an aprotic solvent, so OH would be the stronger nucleophile? Any help would be appreciated!

You....and CHAD alike.....are not going to like this...... Never bet against a Sulfur or Phosphorus nucleophile. These atoms are large....and the electrons are more loosely held. Loose electrons translates into electrons available to do an attack on a sp3 carbon !!!! In virtually all Sn2 processes.....A sulfur nucleophile trumps an Oxygen nucleophile. Another great nucleophile is Cyanide,,,,,,,about as good as Sulfur !!!!!! Going back to this question......SH-....mercaptide would be a better nucleophile than hydroxide.

The effects of solvents are discussed in much detail in the chemical literature. My professor once told me that a solvent can actually accelerate a reaction several million fold !!!! The Organic texts by Wade , Klein, and Bruice books do a wonderful job explaining this.

I hope this helps.

Dr. Romano

 

[universalforceps]

You....and CHAD alike.....are not going to like this...... Never bet against a Sulfur or Phosphorus nucleophile. These atoms are large....and the electrons are more loosely held. Loose electrons translates into electrons available to do an attack on a sp3 carbon !!!! In virtually all Sn2 processes.....A sulfur nucleophile trumps an Oxygen nucleophile. Another great nucleophile is Cyanide,,,,,,,about as good as Sulfur !!!!!! Going back to this question......SH-....mercaptide would be a better nucleophile than hydroxide.

The effects of solvents are discussed in much detail in the chemical literature. My professor once told me that a solvent can actually accelerate a reaction several million fold !!!! The Organic texts by Wade , Klein, and Bruice books do a wonderful job explaining this.

I hope this helps.

Dr. Romano

Yeah, I'm just a little confused on Chad's Nucleophile strength trends based on solvents and what is written in the Odyssey. So if I get this right, Sulfur and Phosphorus are both better nucleophiles than Oxygen, due to being larger and being able to loosely hold onto their electrons, no matter if its in the presence of a protic solvent or aprotic solvent?

 

[DAT Destroyer]

Yeah, I'm just a little confused on Chad's Nucleophile strength trends based on solvents and what is written in the Odyssey. So if I get this right, Sulfur and Phosphorus are both better nucleophiles than Oxygen, due to being larger and being able to loosely hold onto their electrons, no matter if its in the presence of a protic solvent or aprotic solvent?

Yes....This is generally true. It turns out that in a classical SN2 reaction....with CN- for example,,,,,we usually use a polar aprotic solvent such as THF, DMSO, acetonitile, HMPT, etc......the same goes for Sulfur nucleophiles such as CH3S- , HS_, etc. The DAT exam will likely use these solvents......HOWEVER.....You arent going to like this.........These strong nucleophiles mentioned above ....also work quite well in polar protic solvents !!!! For example.....some books use CN- in ethanol.....or HS- in methanol. About 17 years ago....I asked world famous Organic Chemist Maitland Jones,,,,Professor Emeritus at Princeton for an explanation......Dr. Jones told me that nobody had a real single answer.....thus you and I.....must live with this !!!!! I have read many Advanced Organic Chemistry books by March, Carey, Smith, Singh, Kalsi, and Sykes.....and this topic is not really touched. Thus.....Bottom line is this.... A Sulfur nucleophile will almost always trump an Oxygen nucleophile,,,,,,,,and a Phosphorus nucleophile usually trumps a Nitrogen nucleophile regardless of solvent...... Books are written on this stuff,,,,,and I have seen some heated debates among old organic chemistry " geezers " on this. LOL.....I hope this helps.

Dr. Romano

 

[T402]

I have a question about 165 of General Chemistry from DAT Destroyer 2015:

when using NaVa = NbVb, why isn't Vb the final volume of 68ml (20ml Ca(OH)2 + 48ml HBr)?

I have trouble with this equation and with M1V1 = M2V2 in knowing when to use final volume and when to use volume of each species you are combining.

Also-- I thought NaVa = NbVb is used for titration problems and M1V1 = M2V2 is used for dilutions. Do I have this wrong?

Thanks!!

 

[Cool Beans]

You've got the equations and their uses right. When using NaVa = NbVb for titrations, Va represents the volume of acid and Vb the volume of base explaining why you wouldn't use the total volume for either.

Whereas when using M1V1 = M2V2 for dilutions, V2 does indeed represent the total final volume which I think is the source of the confusion above. So keep in mind that:
V1 represents the volume of the original stock
V2 represents the total final volume
V2 - V1 represents the amount of diluent (solvent usually) added

Hope this helps!

 

[T402]

You've got the equations and their uses right. When using NaVa = NbVb for titrations, Va represents the volume of acid and Vb the volume of base explaining why you wouldn't use the total volume for either.

Whereas when using M1V1 = M2V2 for dilutions, V2 does indeed represent the total final volume which I think is the source of the confusion above. So keep in mind that:
V1 represents the volume of the original stock
V2 represents the total final volume
V2 - V1 represents the amount of diluent (solvent usually) added

Hope this helps!

That makes sense. Thank you so much!

 

[510586]

On the answer for 446, did you mean to say anaphase is when sister chromatids are pulled toward opposite poles or is it metaphase?

 

[510586]

On 282, does it form 2 products and we choose the one with the answer choices? Or is the one provided the more stable/major product? Because I think it can react on the other side as well using the other C2H5-O and the other alpha Carbon.

 

[510586]

For 265 of chem part of dat destroyer, why is Mg the best? How would it compare to say Ca or Sr? Would it be better because it is smaller and slightly more EN?

 

[grivacobae]

On DAT Destroyer 2012 for Bio, questions 120 answer choice a)"in prokaryotes, the initiation step of protein synthesis places the initiator codon of the m-RNA, usually AUG and f-Met-t-RNA at the proper site on the ribosome".
Why is this true? mRNA is messenger (processed) RNA, prokaryotes don't process RNA, they go straight to the ribosomes after and while being actively transcribed right?

 

[cacajuate]

On DAT Destroyer 2012 for Bio, questions 120 answer choice a)"in prokaryotes, the initiation step of protein synthesis places the initiator codon of the m-RNA, usually AUG and f-Met-t-RNA at the proper site on the ribosome".
Why is this true? mRNA is messenger (processed) RNA, prokaryotes don't process RNA, they go straight to the ribosomes after and while being actively transcribed right?

mRNA doesn't mean that it's processed.

AUG and f-met are talking about translation. AUG is the start codon for translation. There isn't any sort of processing, it's part of the actual primary sequence.

Yes, prokaryotic transcription and translation are polycistronic.

Check out youtube for good explanations on it.

 

[grivacobae]

mRNA doesn't mean that it's processed.

AUG and f-met are talking about translation. AUG is the start codon for translation. There isn't any sort of processing, it's part of the actual primary sequence.

Yes, prokaryotic transcription and translation are polycistronic.

Check out youtube for good explanations on it.

Oh I see, I always thought messenger RNA meant that is had to go through splicing, and processing and such. Thanks for the clear up!

 

[whitepapertree]

Oh I see, I always thought messenger RNA meant that is had to go through splicing, and processing and such. Thanks for the clear up!

That's pre-mRNA.

In Eukaryotes it goes

DNA - > pre-mRNA - > mRNA

 

[510586]

The problem involves a deuterium exchange,,,,,,,,we replace an H for a D...the problem states EXCESS......thus all the H's must be replaced......via an enolate intermediate. Consult any Orgo text for details.

Dr. Romano


View attachment 192735

Sorry to bring this back up, but when it is D2O / DCl it's like D3O+ since it is in acidic conditions, correct?

 

[510586]

I'm going through the DAT Destroyer biology, and I had a question about number 290. The answer for the question was that all are true statements, however, I remember from animal physiology and looking back at my notes, that norepinephrine and acetylcholine are neurotransmitters of the sympathetic nervous system whereas acetylcholine is the only neurotransmitter of the parasympathetic nervous system.

One of the statements that was deemed true stated: Norepinephrine is the primary neurotransmitter of the sympathetic nervous system.

By primary, does it mean the first neurotransmitter? I thought that would be acetylcholine since it acts on the nicotinic receptor. If someone could help clarify this, that'd be great.

Did you or anyone else find the answer to this? I am a bit stuck on it too. The norepinephrine being primary part.

 

[deleted639067]

Dr. Romano, I'm confused.

In the OChem section for your 2015 DAT Destroyer, Questions 163 and 164 refer to using LiAlH4 with and without using water.

In Q163: You answer the question by reducing a nitrile with LiAlH4, Et2O and H3O+ to form 1-Butanamine. I know that if you use LiAlH4 with H2O it can be extremely reactive and dangerous by producing H2 gas. How would this be different than reducing a nitrile on a benzene ring with LiAlH4 and H2O? I've seen this in a textbook but couldn't seem to find the answer of why H2O could not be used (I know its being used as the acid).

In Q164: You show in the answer as an example reducing the given structure with 1) LiAlH4, Et2O 2)H2O to reduce the ketone, carboxylic acid and the ester.

I'm just confused on when you can and cannot use H2O with LiAlH4. I really appreciate your help and your material...its stellar for preparation of the DAT.

 

[Lnguyen7]

Dr. Romano, I'm confused.

In the OChem section for your 2015 DAT Destroyer, Questions 163 and 164 refer to using LiAlH4 with and without using water.

In Q163: You answer the question by reducing a nitrile with LiAlH4, Et2O and H3O+ to form 1-Butanamine. I know that if you use LiAlH4 with H2O it can be extremely reactive and dangerous by producing H2 gas. How would this be different than reducing a nitrile on a benzene ring with LiAlH4 and H2O? I've seen this in a textbook but couldn't seem to find the answer of why H2O could not be used (I know its being used as the acid).

In Q164: You show in the answer as an example reducing the given structure with 1) LiAlH4, Et2O 2)H2O to reduce the ketone, carboxylic acid and the ester.

I'm just confused on when you can and cannot use H2O with LiAlH4. I really appreciate your help and your material...its stellar for preparation of the DAT.

Well, the reaction is carried out in 2 steps. The first step is with LiAlH4 and Et2O but no H2O. After the first step, then you add H2O. It's not LiAlH4, Et2O AND H2O in 1 step.

 

[florida21]

Does an ester or an ether have acidic hydrogens? That Destroyer says that an ether doesn't have an acidic hydrogen however, wouldn't the carbon next to the oxygen lose an H and this would be stabilized by resonance the oxygen?

 

[DetermineDent]

On 2015 Version of DAT Destroyer:
GChem #12
Could we have used deltaT=-iKfm for this problem?
Cause when I used that, I got -4.2 for deltaT.

Does the explanation in the solution on using "i" always apply for boiling pt. and melting pt.?

 

[DAT Destroyer]

Dr. Romano, I'm confused.

In the OChem section for your 2015 DAT Destroyer, Questions 163 and 164 refer to using LiAlH4 with and without using water.

In Q163: You answer the question by reducing a nitrile with LiAlH4, Et2O and H3O+ to form 1-Butanamine. I know that if you use LiAlH4 with H2O it can be extremely reactive and dangerous by producing H2 gas. How would this be different than reducing a nitrile on a benzene ring with LiAlH4 and H2O? I've seen this in a textbook but couldn't seem to find the answer of why H2O could not be used (I know its being used as the acid).

In Q164: You show in the answer as an example reducing the given structure with 1) LiAlH4, Et2O 2)H2O to reduce the ketone, carboxylic acid and the ester.

I'm just confused on when you can and cannot use H2O with LiAlH4. I really appreciate your help and your material...its stellar for preparation of the DAT.

As a RULE.....NEVER use the white powder LiAlH4 with water.....it makes an explosive cocktail !!!! You must do it in steps.....thus we write it as 1. LiAlH4, Et20 ..then 2. Water or H30+. This is just a fine point.....

For the DAT just make sure you know that NaBH4 reduces aldehydes, ketones, and acyl halides,,,,,,,,while the POWERFUL and MIGHTY LiAlH4 reduces aldehydes, ketones, acyl halides, esters, nitriles and most importantly carboxy acids !

Hope this helps.

Dr. Romano