Official DAT Destroyer Q&A Thread

[densaugeo]

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!

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[DAT Destroyer]

If a reaction is Endothermic.....an increase in temperature will generally move the reaction to the RIGHT,,,,,thus the K value will increase. If the reaction was exothermic, an increase in temperature will shift the K value to the LEFT and the K value would decrease. . In this problem, we see a decrease in temperature AND a decrease in K. This is what we would find for an endothermic reaction. Endothermic reactions are only enhanced with an increase in temperature, not a decrease.

I hope this helps.

 

[GDragon_1988]

If a reaction is Endothermic.....an increase in temperature will generally move the reaction to the RIGHT,,,,,thus the K value will increase. If the reaction was exothermic, an increase in temperature will shift the K value to the LEFT and the K value would decrease. . In this problem, we see a decrease in temperature AND a decrease in K. This is what we would find for an endothermic reaction. Endothermic reactions are only enhanced with an increase in temperature, not a decrease.

I hope this helps.

thank you!

 

[mrdeez]

Confusing wording on BIO #447 2016, someone please help me out.

It says that an autosomal recessive CONDITION is seen in 1 in every 50 people, but is symptom free. If a male and female possibly CARRY the gene, what is the probability that they have a diseased child?

When I started thinking about this, I interpreted the phrase "an autosomal recessive condition is seen" as meaning an affected individual is observed. Therefore, that individual's genotype must be aa (autosomal recessive). From my understanding, a "CARRIER" of a disease usually refers to someone who is unaffected by the disease but carries the recessive allele, in other words, they are heterozygous for the trait. So shouldn't the phrase "a male and female possibly carry the gene" be interpreted as they are both heterozygous?

The solution states that each parent has a 1/50 chance to carry the gene. This confuses me because the problem said the CONDITION is seen in 1/50 people, not heterzygote carriers are seen in 1/50 people. The solution goes on to say that there is a 25% chance of them having an affected child (autosomal recessive) which implies they were heterozygotes all along. If this is the case, then the parents DO NOT HAVE THE CONDITION, and the 1/50 chance stated at the beginning of the problem is not referring to them.

Am I losing my mind here?

 

[DAT Destroyer]

Confusing wording on BIO #447 2016, someone please help me out.

It says that an autosomal recessive CONDITION is seen in 1 in every 50 people, but is symptom free. If a male and female possibly CARRY the gene, what is the probability that they have a diseased child?

When I started thinking about this, I interpreted the phrase "an autosomal recessive condition is seen" as meaning an affected individual is observed. Therefore, that individual's genotype must be aa (autosomal recessive). From my understanding, a "CARRIER" of a disease usually refers to someone who is unaffected by the disease but carries the recessive allele, in other words, they are heterozygous for the trait. So shouldn't the phrase "a male and female possibly carry the gene" be interpreted as they are both heterozygous?

The solution states that each parent has a 1/50 chance to carry the gene. This confuses me because the problem said the CONDITION is seen in 1/50 people, not heterzygote carriers are seen in 1/50 people. The solution goes on to say that there is a 25% chance of them having an affected child (autosomal recessive) which implies they were heterozygotes all along. If this is the case, then the parents DO NOT HAVE THE CONDITION, and the 1/50 chance stated at the beginning of the problem is not referring to them.

Am I losing my mind here?

You are talking about question 471, not 477.
Your logic is correct. However, the question said "Condition" not the disease. Meaning, people have the allele, and are carriers, but do not have the disease. Condition, does not always mean fully manifested disease. That is why it said, Symptom free.
Your Mendelian Genetics analysis was correct.
However, the question asked something different. The asked if each parent has 1/50 chance to carry the gene. Since it sait Symptom free.
Hope this helps.

 

[mrdeez]

You are talking about question 471, not 477.
Your logic is correct. However, the question said "Condition" not the disease. Meaning, people have the allele, and are carriers, but do not have the disease. Condition, does not always mean fully manifested disease. That is why it said, Symptom free.
Your Mendelian Genetics analysis was correct.
However, the question asked something different. The asked if each parent has 1/50 chance to carry the gene. Since it sait Symptom free.
Hope this helps.

It is question #447 in the 2016 destroyer.

Just out of curiosity, will the DAT also have questions that are based on semantic differences between words as similar as "condition" and "disease"? I haven't checked my text yet but it seems like these could easily be confused.

"A disease is a particular abnormal condition, a disorder of a structure or function, that affects part or all of an organism. The study of disease is called pathology which includes the study of cause. Disease is often construed as a medical condition associated with specific symptoms and signs."

Disease - Wikipedia

It seems like they are almost synonymous in this definition. I will look at Campbell's Bio and some others to see if there is a better distinction in print. Regardless of the two definitions, can't both a "condition" and a "disease" be asymptomatic? For example, using your definition, heterozygotes are asymptomatic, but a genetic disease like hypothyroidism can also be asymptomatic?

 

[GDragon_1988]

Hey Dr. Romano, I have a question about Gen Chem #318 (2016 DAT Destroyer)

if any compound has radical characteristics, can I assume that it'll form a dimer?

 

[GDragon_1988]

Hey Dr. Romano, Bio #532 (dat destroyer 2016). It says normal female, but can i assume it was heterozygous as well? if on my exam, it says normal gender, do i automatically have to assume the individual isn't a carrier?

 

[DAT Destroyer]

Hey Dr. Romano, Bio #532 (dat destroyer 2016). It says normal female, but can i assume it was heterozygous as well? if on my exam, it says normal gender, do i automatically have to assume the individual isn't a carrier?

No. That depends on the results of the cross. If normal female and normal male yield mutant offspring, then you can assume heterozygosity.
If, Normal parents have as a result a normal offspring, you cannot assume heterozygosity.

Hope this helps.

 

[GDragon_1988]

No. That depends on the results of the cross. If normal female and normal male yield mutant offspring, then you can assume heterozygosity.
If, Normal parents have as a result a normal offspring, you cannot assume heterozygosity.

Hope this helps.

thank You!

 

[IWCBTYJ]

Dr. Romano,

This may be a very silly and dumb question, but for question 1 in General Chemistry for Destroyer 2016, we are said to consider Hydroxylamine as a base because you gave us the Kb of 1.1 x10^-8. However, when I was initially solving this problem, I wanted to compare its acidity vs basicity so i compared its Kb vs Ka and found that Ka was higher and that pKA of this was around 6 which made it slightly acidic and thus chose the reaction that represented NH2OH as an acid instead of base. Is my train of thought wrong?

As always, your help is very appreciated!

 

[predent21aahopefully]

Hello,

Question 66 of 2016 Dat Destroyer General Chemistry, I thought that if we were given the question of producing the rate law of the reaction that we would just simply use the rate law of the slow step including its coefficients etc. I am lost about what are the first steps that I should take to answer this question I am confused by the answer feedback in the book it seems to be so many steps when I just learned from videos that the slow step will be the rate law of the reaction. Please can anybody clear up the confusion that I have

 

[predent21aahopefully]

Also can anybody explain polarity I always see myself missing these questions in terms of organic and general chemistry are we supposed o draw these molecules in a three dimensional manner or two basically and do we need to draw that molecule in its specific molecular geometry for both ten chem and organic. Hopefully I make sense here basically need help with tackling questions which ask you which molecule is/are polar.

 

[DAT Destroyer]

Dr. Romano,

This may be a very silly and dumb question, but for question 1 in General Chemistry for Destroyer 2016, we are said to consider Hydroxylamine as a base because you gave us the Kb of 1.1 x10^-8. However, when I was initially solving this problem, I wanted to compare its acidity vs basicity so i compared its Kb vs Ka and found that Ka was higher and that pKA of this was around 6 which made it slightly acidic and thus chose the reaction that represented NH2OH as an acid instead of base. Is my train of thought wrong?

As always, your help is very appreciated!

You are overthinking this question. Your logic deals with the direction that the equilibrium will lie, and that is not what is being asked. Since amines are BASES, and will react as such, a small amount of OH- ions must be produced. Many times in organic chemistry we focus on a reaction that is not necessarily going in the forward reaction to a great extent. the Aldol condensation is a fine example.

Hope this helps.

Dr. Romano

 

[GDragon_1988]

Hey Dr. Romano, could you elaborate more on Orgo #303 in (2016 DAT Destroyer)

I understand fatty acid could be a potential answer choice but, why wouldn't steroid by an option? Steroids have many carbons and some of them have oxygen's in the compound. Also, is anhydride not an option because they aren't normally long chained carbons?

Thanks

 

[DAT Destroyer]

Hello,

Question 66 of 2016 Dat Destroyer General Chemistry, I thought that if we were given the question of producing the rate law of the reaction that we would just simply use the rate law of the slow step including its coefficients etc. I am lost about what are the first steps that I should take to answer this question I am confused by the answer feedback in the book it seems to be so many steps when I just learned from videos that the slow step will be the rate law of the reaction. Please can anybody clear up the confusion that I have

Sometimes the slow step gives you the correct answer, and you are done quickly. If the rate law contains an INTERMEDIATE, you must substitute as shown in the solution to get rid of the intermediate. An intermediate will NOT appear in the final rate law expression.

Hope this helps.

 

[wizkidz]

Dr. Romano- I was wondering how x was found to be 1/2 in Gen Chem 2016 number 85. where did the 2x=1 come from in the solution? thank you !

 

[Trave_]

Latest version of Destroyer, GC #43 -

Mike's Videos mentioned that for boiling and melting point questions, check the molecular weight before checking intermolecular forces. This still lead me to pick the correct answer since it had the lowest molecular weight, but your solution guide notes that the reasoning is due to intermolecular forces. Should my first go-to for these type of questions be intermolecular forces or molecular weight?

 

[DAT Destroyer]

Latest version of Destroyer, GC #43 -

Mike's Videos mentioned that for boiling and melting point questions, check the molecular weight before checking intermolecular forces. This still lead me to pick the correct answer since it had the lowest molecular weight, but your solution guide notes that the reasoning is due to intermolecular forces. Should my first go-to for these type of questions be intermolecular forces or molecular weight?

I highly recommend that you reference sources written by PhD chemists. Checking molecular weights before intermolecular forces is usually a HORRIBLE way to approach a problem and results are often erroneous. For example, H2S weighs 34 amu....while water only weighs 18 amu..yet water has the higher boiling and melting point. .....INTERMOLECULAR forces normally DOMINATE. If you are looking at Noble gases, hydrocarbons, or halogens,,,,,,Molecular weight would work.....BUT only because intermolecular forces dominate. The book by Raymond Chang nicely discusses all this.

I hope this helps.

Dr. Romano

 

[dentist ex machina]

@orgoman22

I have a quick question about organic chemistry.

I know that as essentially carbanions, Grignard reagents are such strong bases that you need to avoid any acidic protons in order to use them as nucleophiles. With that being said, why don't they deprotonate the alpha hydrogen of aldehydes and ketones in an acid base reaction instead of adding to the carbonyl? With a pKa of around 20, I don't see why we wouldn't just generate an enolate as we do when using other strong bases (especially in instances where we use a very bulky, hindered species like the phenyl Grignard reagent).

 

[DAT Destroyer]

@orgoman22

I have a quick question about organic chemistry.

I know that as essentially carbanions, Grignard reagents are such strong bases that you need to avoid any acidic protons in order to use them as nucleophiles. With that being said, why don't they deprotonate the alpha hydrogen of aldehydes and ketones in an acid base reaction instead of adding to the carbonyl? With a pKa of around 20, I don't see why we wouldn't just generate an enolate as we do when using other strong bases (especially in instances where we use a very bulky, hindered species like the phenyl Grignard reagent).

You have asked a very sophisticated question that we sometimes examine in Advanced Organic Chemistry. The Grignard is different from many bases such as HO- or ethoxide, or LDA....... which we often use to remove an alpha hydrogen. A reaction can either be under Charge or Orbital control. If charge control, we attack the carbonyl group,,,,,,if Orbital control, we attack an H or attack a beta carbonyl as seen in a Michael -type reaction process. We divide nucleophiles into what we call hard or charged-control, or Soft which is orbital-controlled. This is done experimentally. The Grignard or alkyl Lithium reagent falls into the category of Hard.....This means, it more easily reacts with the carbonyl group, than to attack the hydrogen. The gap between Homo ( nucleophile ) and Lumo ( the hydrogen ) are quite far, and not thermodynamically advantageous. Thus, the bottom line is this......Grignards attack carbonyl groups, bases such as HO-, Ethoxide, methoxide, etc can interact in a Homo-Lumo advantageous reaction to give an enolate anion. I hope this helps, on a very difficult question at the Undergrad level.

Dr. Romano

 

[IWCBTYJ]

You are overthinking this question. Your logic deals with the direction that the equilibrium will lie, and that is not what is being asked. Since amines are BASES, and will react as such, a small amount of OH- ions must be produced. Many times in organic chemistry we focus on a reaction that is not necessarily going in the forward reaction to a great extent. the Aldol condensation is a fine example.

Hope this helps.

Dr. Romano

Dr. Romano,

Thank you so much, this actually clears so many things up!

If you don't mind, I have another question perhaps you could clarify for me!

For Orgo question 255 on 2016 destroyer, you state that despite having a bulky base, you are still able to remove the most acidic hydrogen. I guess my confusion comes from 1) does the aromatic ring on the beta carbon not impose even more steric hinderance? 2) How do you decide when the steric is enough to stop the base from taking the most acidic proton vs taking the easier, less acidic proton? I feel like there isn't a very clear cut line, as thats the nature's way, in terms of Steric hinderance vs taking most acidic proton, but if you could clarify this, it would be very much appreciated. Thank you so so much! Looking to learn from you yet again.

 

[dentist ex machina]

You have asked a very sophisticated question that we sometimes examine in Advanced Organic Chemistry. The Grignard is different from many bases such as HO- or ethoxide, or LDA....... which we often use to remove an alpha hydrogen. A reaction can either be under Charge or Orbital control. If charge control, we attack the carbonyl group,,,,,,if Orbital control, we attack an H or attack a beta carbonyl as seen in a Michael -type reaction process. We divide nucleophiles into what we call hard or charged-control, or Soft which is orbital-controlled. This is done experimentally. The Grignard or alkyl Lithium reagent falls into the category of Hard.....This means, it more easily reacts with the carbonyl group, than to attack the hydrogen. The gap between Homo ( nucleophile ) and Lumo ( the hydrogen ) are quite far, and not thermodynamically advantageous. Thus, the bottom line is this......Grignards attack carbonyl groups, bases such as HO-, Ethoxide, methoxide, etc can interact in a Homo-Lumo advantageous reaction to give an enolate anion. I hope this helps, on a very difficult question at the Undergrad level.

Dr. Romano
.

Thanks for your help!

 

[GDragon_1988]

Hey Dr. Romano, for Gen Chem #206 (DAT Destroyer 2016), i thought only temperature could change the rate constant?

 

[DAT Destroyer]

Hey Dr. Romano, for Gen Chem #206 (DAT Destroyer 2016), i thought only temperature could change the rate constant?

No......Do not confuse rate constant with equilibrium constant. A rate constant can be changed by factors such as temperature, solvents, structure, pressure, and catalysts. An equilibrium constant is NOT changed by factors such as pressure, catalysts, etc...but is changed by temperature. This is a commonly asked " trick " question. I hope this helps.

 

[DAT Destroyer]

Hey Dr. Romano, for Gen Chem #206 (DAT Destroyer 2016), i thought only temperature could change the rate constant?

When are you taking the DAT?

 

[GDragon_1988]

When are you taking the DAT?

I take my DAT on July 14th

 

[Lalibila]

Hi I have some questions about dat destroyer
For example, is general chemistry a set of tests. What I mean, does every 30 questions represent random questions from all of the chapters in gen chem or are the questions organized by topics? like every 20 questions correspond to a certain topic.
Same question goes for the qr section in the dat destroyer.
Also, how many questions are there per section? Bio, genchem, ochem, and qr.
Finally, how many questions are recommended to solve each day?

I had the same question regarding the question distribution in the sections if someone can clarify.


Sent from my iPhone using SDN mobile

 

[GDragon_1988]

Hey Dr. Romano, for Orgo #204 (2016 DAT Destroyer), on the actual dat, would they give us the pka values of an amino acid or are we suppose to know it?

 

[Prima Donna]

Had a question about number 271 in orgo section. I thought that anything with more than 7 carbons meant that it would not be planar thus not aromatic. Or would this have something to do with it being a bicyclic ? I understood why everything else is true but not answer A. Thanks.

 

[DAT Destroyer]

Had a question about number 271 in orgo section. I thought that anything with more than 7 carbons meant that it would not be planar thus not aromatic. Or would this have something to do with it being a bicyclic ? I understood why everything else is true but not answer A. Thanks.

Whoa Whoa Whoa.....where did you get this notion ? Many large aromatic rings are not only common but used all the time in organic chemistry. Indole, quinoline, naphthalene, anthracene, and the monster porphyrin ring making up hemoglobin are all large and aromatic !!!! If a large ring could become aromatic, it would likely not twist since this would break up the parallel array of p orbitals. If we get larger rings such as seen in cyclooctatetraene , this molecule would be anti-aromatic if planar, but by twisting, the orbitals " uncouple " and the molecules escapes its horrendous anti-aromatic fate. This molecule is Non Aromatic !!

I hope this helps.

Dr. Romano

 

[predent21aahopefully]

Whoa Whoa Whoa.....where did you get this notion ? Many large aromatic rings are not only common but used all the time in organic chemistry. Indole, quinoline, naphthalene, anthracene, and the monster porphyrin ring making up hemoglobin are all large and aromatic !!!! If a large ring could become aromatic, it would likely not twist since this would break up the parallel array of p orbitals. If we get larger rings such as seen in cyclooctatetraene , this molecule would be anti-aromatic if planar, but by twisting, the orbitals " uncouple " and the molecules escapes its horrendous anti-aromatic fate. This the molecule is Non Aromatic !!

I hope this helps.

Dr. Romano

 

[Prima Donna]

Whoa Whoa Whoa.....where did you get this notion ? Many large aromatic rings are not only common but used all the time in organic chemistry. Indole, quinoline, naphthalene, anthracene, and the monster porphyrin ring making up hemoglobin are all large and aromatic !!!! If a large ring could become aromatic, it would likely not twist since this would break up the parallel array of p orbitals. If we get larger rings such as seen in cyclooctatetraene , this molecule would be anti-aromatic if planar, but by twisting, the orbitals " uncouple " and the molecules escapes its horrendous anti-aromatic fate. This molecule is Non Aromatic !!

I hope this helps.

Dr. Romano

Oh okay that makes sense. I just remember writing down from Chad's videos that if the compound was more than 7 Carbons then it was not going to be planar and thus not aromatic (he gave the example of a conjugated 8 member carbon ring and said it was not planar and thus non aromatic). Gonna have to go rewatch that video maybe. Thanks for the help !

 

[spdental]

For the GC solutionon question 151 it says that hydrogen bonding will cause the solid-liquid line to be skewed to the left, and in the answer key it says this again; however the h-bond for water has the line skewed to the right, not the left. Is there a mistake in this question?

 

[DAT Destroyer]

For the GC solutionon question 151 it says that hydrogen bonding will cause the solid-liquid line to be skewed to the left, and in the answer key it says this again; however the h-bond for water has the line skewed to the right, not the left. Is there a mistake in this question?

You are focusing on the wrong line. The line at the left of the graphs represent the solid-liquid line,,,,,,For water, it is indeed skewed to the LEFT !!! For further clarity, the Raymond Chang or Brown-LeMay text shows it nicely as well.

Hope this helps.

Dr. Jim Romano

 

[jya5ab]

@orgoman22

Hello! For Destroyer 2016 OC #144:

Based on the IUPAC rule that you must start counting at the end that gives you the lowest numbers for substituents, wouldn't you start counting from the left, so that methyl is #2, ethyl is #3, and -OH is #6? This would be answer E (3-ethyl-2-methyl-6-octanol). However, the back of the book says the answer is D (6-ethyl-7-methyl-3-octanol). Why you would start counting from the end closest to the -OH group, even though this would give you higher numbers for all substituents?


Edit: another general question I have is, when a question asks "which nucleophile is the strongest"?, with no reference to the solvent it's in, should we assume that the question is asking in reference to a Protic solvent (bigger nucleophiles = stronger)? I ask since the answer would be different in reference to an Aprotic solvent (smaller nucleophiles = stronger).

Thank you!

 

[IWCBTYJ]

Dr. Romano,

I was hoping you could answer perhaps another one of my questions!

For Orgo question 255 on 2016 destroyer, you state that despite having a bulky base, you are still able to remove the most acidic hydrogen. I guess my confusion comes from 1) does the aromatic ring on the beta carbon not impose even more steric hinderance? 2) How do you decide when the steric is enough to stop the base from taking the most acidic proton vs taking the easier, less acidic proton? I feel like there isn't a very clear cut line, as thats the nature's way, in terms of Steric hinderance vs taking most acidic proton, but if you could clarify this, it would be very much appreciated. Thank you so so much! Looking to learn from you yet again.

 

[DAT Destroyer]

Dr. Romano,

I was hoping you could answer perhaps another one of my questions!

For Orgo question 255 on 2016 destroyer, you state that despite having a bulky base, you are still able to remove the most acidic hydrogen. I guess my confusion comes from 1) does the aromatic ring on the beta carbon not impose even more steric hinderance? 2) How do you decide when the steric is enough to stop the base from taking the most acidic proton vs taking the easier, less acidic proton? I feel like there isn't a very clear cut line, as thats the nature's way, in terms of Steric hinderance vs taking most acidic proton, but if you could clarify this, it would be very much appreciated. Thank you so so much! Looking to learn from you yet again.

When it comes to acidity, steric hinderance does not normally cause that many problems. Believe it or not, the phenyl group is not that big, consequently there is plenty of room. Let us say there are two alpha protons, as in 2-pentanone. Now we have a situation in which we have a CHOICE !!!! If given a choice, then kinetics dominates the reaction and the outer hydrogen is removed fastest. Even though the inner proton would give the more stable enolate and hence the thermodynamic product. We see this nicely exemplified in the Haloform reaction. The base removes the outer hydrogen over an inner hydrogen. When there is no competition, a base usually doesn't not have the same problems with steric interference as do nucleophiles. For example, a tertiary halide NEVER will do an SN2, but EASILY will do an E2. In Advanced Organic Chemistry, we can debate this even further, but I think you get the point !!!

I hope this helps.

Dr. Romano

 

[IWCBTYJ]

When it comes to acidity, steric hinderance does not normally cause that many problems. Believe it or not, the phenyl group is not that big, consequently there is plenty of room. Let us say there are two alpha protons, as in 2-pentanone. Now we have a situation in which we have a CHOICE !!!! If given a choice, then kinetics dominates the reaction and the outer hydrogen is removed fastest. Even though the inner proton would give the more stable enolate and hence the thermodynamic product. We see this nicely exemplified in the Haloform reaction. The base removes the outer hydrogen over an inner hydrogen. When there is no competition, a base usually doesn't not have the same problems with steric interference as do nucleophiles. For example, a tertiary halide NEVER will do an SN2, but EASILY will do an E2. In Advanced Organic Chemistry, we can debate this even further, but I think you get the point !!!

I hope this helps.

Dr. Romano

Ahh.. That makes so much more sense! Thank you so much!!!! very much appreciated

 

[DAT Destroyer]

Ahh.. That makes so much more sense! Thank you so much!!!! very much appreciated

Great, don't forget to like my post..

Dr. Romano

 

[MickeyMug]

@orgoman22 for 2017 bio question #481:

I though that the answer would be 6.25% because if we start with a double stranded DNA, wouldn't both of them replicate at the same time and give us 4 strands after the first round of replication, then 8, 16, and 32?

Thanks in advance!

 

[mrdeez]

Gen Chem #218 in 2016 version:
Which can function as lewis acids?
a) AlCl3
b) BF3
c) H2O
d) NH2-
e) A and B

The answer is A and B but it should be A B and C. Water receives an electron pair all the time. It becomes hydroxide in a basic solution and acts as an electrophile/lewis acid. In the example I just mentioned, it is both a lewis acid and a bronsted acid. The terms are not mutually exclusive. This question does not make sense. Help!

 

[GDragon_1988]

Hey Dr. Romano, both fibroblasts and chondrocytes produce collagen, but is one more favored?

 

[DAT Destroyer]

@orgoman22 for 2017 bio question #481:

I though that the answer would be 6.25% because if we start with a double stranded DNA, wouldn't both of them replicate at the same time and give us 4 strands after the first round of replication, then 8, 16, and 32?

Thanks in advance!

The question assumes that you are starting with 1 DNA strand, not 2.

 

[DAT Destroyer]

Hey Dr. Romano, both fibroblasts and chondrocytes produce collagen, but is one more favored?

Chondrocytes are mainly for making cartilage, but fibroblasts are mainly for wound healing and extracellular matrix synthesis.

Hope this helps.

 

[GDragon_1988]

Chondrocytes are mainly for making cartilage, but fibroblasts are mainly for wound healing and extracellular matrix synthesis.

Hope this helps.

Thank you!

 

[hsjordan24]

Dr. Romano or anyone that understands this,

Can you please explain #218 in 2017 Bio Destroyer? It says "Which DNA sequence is a palindrome and could be a potential restriction enzyme site?"
A. GAATCG
B. CCTAGG
C. AAAAA
D. GGGGG
E. GGCCGG

I'm confused on this concept although its probably very simple once I see it explained well. B is the correct answer.

 

[MickeyMug]

Dr. Romano or anyone that understands this,

Can you please explain #218 in 2017 Bio Destroyer? It says "Which DNA sequence is a palindrome and could be a potential restriction enzyme site?"
A. GAATCG
B. CCTAGG
C. AAAAA
D. GGGGG
E. GGCCGG

I'm confused on this concept although its probably very simple once I see it explained well. B is the correct answer.

"A palindrome is read the same from left to right as it is from right to left."
If you take the compliment of every answer choice you'll get
A. CTTAGC
B. GGATCC
C. TTTTT
D. CCCCC
E. CCGGCC
As you can see, only choice B and its compliment is read the same from left to right as it is from right to left.

Hope this helps!

 

[hsjordan24]

"A palindrome is read the same from left to right as it is from right to left."
If you take the compliment of every answer choice you'll get
A. CTTAGC
B. GGATCC
C. TTTTT
D. CCCCC
E. CCGGCC
As you can see, only choice B and its compliment is read the same from left to right as it is from right to left.

Hope this helps!

Yes! That makes a lot of sense, I did not realize to take the compliment of the answer choices themselves, duh. Thanks.

 

[UNCafDDS]

I have been working through the 2016 Destroyer book, and I am stumped on Organic Chemistry question #70.
For the conversion, I don’t understand how HCl could not be an appropriate reagent. The explanation says that rearrangement would occur; however, I thought rearrangement would not be possible since the LG is on a primary carbon, and the reaction would occur via SN2 (thus no rearrangement, just inversion of stereochemistry if applicable)? Thanks!

 

[DAT Destroyer]

I have been working through the 2016 Destroyer book, and I am stumped on Organic Chemistry question #70.
For the conversion, I don’t understand how HCl could not be an appropriate reagent. The explanation says that rearrangement would occur; however, I thought rearrangement would not be possible since the LG is on a primary carbon, and the reaction would occur via SN2 (thus no rearrangement, just inversion of stereochemistry if applicable)? Thanks!

A primary halide usually will not undergo a shift UNLESS there is branching as depicted in this problem. We see a CONCERTED shift to avoid forming the high energy carbocation. Tricky indeed.
I hope this helps. If you need more clarity, it is discussed in the David Klein and Thomas Sorell PhD textbook.

Dr. Romano