The Official 3/23/13 MCAT Thread

[Redpancreas]

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Figured I'd start this one out. I'll be registering for the MCAT first thing tomorrow. Who else is taking it on this date? How do you all plan on studying over the school year?

 

[dellian101]

have you guys started practice exams yet? i'm trying to get through berkeley review books and keep getting 4-5 on each end of chapter exam and freak out mode is: on!

 

[slz1900]

have you guys started practice exams yet? i'm trying to get through berkeley review books and keep getting 4-5 on each end of chapter exam and freak out mode is: on!

Is 4 to 5 your scaled score, or are you getting 4 to 5 right per passage? Getting 5 out of 7 consistently puts you over 70% which is generally regarded as a good score.

 

[NuttyEngDude]

First you hate them. Then you get used to them. Then you start to like them. I'll tell you how I really feel after the real one, which will be #27 if I use all of what I have available 🙂

I'm using gold standard right now but their verbal is crap, so I'm doing the cbt sciences with a full ek verbal in between. I'm seeing linear improvement, with my last two tests the same at 11/10/11. I'm convinced I'm leaving points on the table with calculation and goofball errors so I'm adjusting my strategy to correct. Plan is to insert an aamc this week and see how I do on a more realistic test.

I might get the gold standard tests, just because they're so cheap.. 10 for $150 or something?

have you guys started practice exams yet? i'm trying to get through berkeley review books and keep getting 4-5 on each end of chapter exam and freak out mode is: on!

I wouldnt freak out until you take a practice exam. and according to SN2ED's schedule, if you have a month to do practice exams you are on track. I made a separate schedule that has me finishing CR by the end of the month giving me 2 months for practice exams but I'm having difficulties sticking to it. for all intents and purposes i'm a retaker, and captain cisko has been prepping for like a year now 😛

 

[gettheleadout]

See yesterday's Fact here

Today's fact concerns DNA structure!

For today, I'll let this great picture do the talking:

 

[Captain Sisko]

I might get the gold standard tests, just because they're so cheap.. 10 for $150 or something?




I wouldnt freak out until you take a practice exam. and according to SN2ED's schedule, if you have a month to do practice exams you are on track. I made a separate schedule that has me finishing CR by the end of the month giving me 2 months for practice exams but I'm having difficulties sticking to it. for all intents and purposes i'm a retaker, and captain cisko has been prepping for like a year now 😛

Cheaper, old sport!

Go on eBay, you can purchase a 6 month access for $100. Just search for gs mcat.

 

[Albein]

So tired. I keep trying to catch up but it's not working, I'll have to push the schedule out a few days. That's ok because i've still got a lot of time after I've completed content review.

how's everyone else doing, when do you guys plan to finish content review?

I'm in the same boat as you my friend. I make very little progress in terms of catching up. Hopefully some of these chapters are a little shorter and I can get through 2 a day.

For those following SN2's study schedule, I'm having trouble deciding on something. I purchased the EK set during my first go around with this test and did only a few chapters and then took a PR course. I've been following the schedule in every aspect except for the Bio Part; I've only been using BR bio for content review and passages. Are there any suggestions for how I can take the end of chapter practice exams with the EK? My biology has been very hit or miss and I feel like I'm forgetting a lot of it as I move on. Thanks and happy studying (if there was such a thing).

 

[Jr MD]

First day of class..ugghh...woke up at 6 to start studying...I'm pooped...

Sent from my T-Mobile myTouch Q using SDN Mobile

 

[Captain Sisko]

See yesterday's Fact here

Today's fact concerns DNA structure!

For today, I'll let this great picture do the talking:

Questions for the GTLO "Passage":

1) Histones are proteins that bind to DNA through ionic interactions. Histone residues responsible for bonding to the DNA are most likely to be:

a) Histamine

b) Glutamate

c) Lysine

d) Glycine


2) Core histones involve histone proteins H2a, H2b, H3 and H4. Two each of these proteins complex to form an octamer at the center of each nucleosome. The octamer is an example of:

a) Prosthetic Groups

b) Tertiary Structure

c) Quaternary Structure

d) Nucleophilic Attraction


3) Histone charges that enable binding to DNA are neutralized by the addition of an acetyl group. The enzyme and cofactor responsible for this reaction are, respectively:

a) Histone acetyl kinase, B6

b) Histone acetyl kinase, Acetyl CoA

c) Histone acetyl transferase, B6

d) Histone acetyl transferase, Acetyl CoA


4) Histones are made in the:

a) Nucleus

b) Histosome

c) Cytoplasm

d) Nucleolus


5) Transcription of rRNA takes place in:

a) Ribosomes

b) Nucleoplasm

c) Nucleolus

d) Rough Endoplasmic Reticulum


6) The core histones range between 11 and 15 kDa (1 Da = 1 g/mol). With the average amino acid size being approximately 110 Da, what is the approximate length of a post-transcriptionally modified mRNA strand used to code for H3?

a) 10,000 bases

b) 4,000 bases

c) 1,000 bases

d) 400 bases

 

[Captain Sisko]

Just thought I'd have fun thinking of what they could ask. Share comments and suggestions. I'll post answers later.

 

[EphemeralRose3]

I think these are the answers!

1) Histones are proteins that bind to DNA through ionic interactions. Histone residues responsible for bonding to the DNA are most likely to be:

a) Histamine

b) Glutamate

c) Lysine

d) Glycine


2) Core histones involve histone proteins H2a, H2b, H3 and H4. Two each of these proteins complex to form an octamer at the center of each nucleosome. The octamer is an example of:

a) Prosthetic Groups

b) Tertiary Structure

c) Quaternary Structure

d) Nucleophilic Attraction


3) Histone charges that enable binding to DNA are neutralized by the addition of an acetyl group. The enzyme and cofactor responsible for this reaction are, respectively:

a) Histone acetyl kinase, B6

b) Histone acetyl kinase, Acetyl CoA

c) Histone acetyl transferase, B6

d) Histone acetyl transferase, Acetyl CoA ** Not too sure though


4) Histones are made in the:

a) Nucleus

b) Histosome

c) Cytoplasm

d) Nucleolus


5) Transcription of rRNA takes place in:

a) Ribosomes

b) Nucleoplasm

c) Nucleolus

d) Rough Endoplasmic Reticulum


6) The core histones range between 11 and 15 kDa (1 Da = 1 g/mol). With the average amino acid size being approximately 110 Da, what is the approximate length of a post-transcriptionally modified mRNA strand used to code for H3?

a) 10,000 bases

b) 4,000 bases

c) 1,000 bases


d) 400 bases

 

[Albein]

just a helpful hint/advice. From what I remember while doing AAMC practice tests last year, they love giving an experiment setup passage similar to Thomson existence of opposite charges or Millikan oil drop experiment. In my opinion, the BR Physics, Gen Chem, and orgo cover these types of experiments and suggest how they can be presented, BR Biology thus far (I just finished cell structure and function and viruses), doesn't really go over and types of experiments. For those of you who have PR bio, they have an experiment section in the end. If there is enough of a demand by those of you don't have it, I can scan it and upload it. It especially helped me understanding antibodies and the serological tests along with primary and secondary antibody binding.

 

[gettheleadout]

Questions for the GTLO "Passage":

1) Histones are proteins that bind to DNA through ionic interactions. Histone residues responsible for bonding to the DNA are most likely to be:

a) Histamine

b) Glutamate

c) Lysine

d) Glycine


2) Core histones involve histone proteins H2a, H2b, H3 and H4. Two each of these proteins complex to form an octamer at the center of each nucleosome. The octamer is an example of:

a) Prosthetic Groups

b) Tertiary Structure

c) Quaternary Structure

d) Nucleophilic Attraction


3) Histone charges that enable binding to DNA are neutralized by the addition of an acetyl group. The enzyme and cofactor responsible for this reaction are, respectively:

a) Histone acetyl kinase, B6

b) Histone acetyl kinase, Acetyl CoA

c) Histone acetyl transferase, B6

d) Histone acetyl transferase, Acetyl CoA


4) Histones are made in the:

a) Nucleus

b) Histosome

c) Cytoplasm

d) Nucleolus


5) Transcription of rRNA takes place in:

a) Ribosomes

b) Nucleoplasm

c) Nucleolus

d) Rough Endoplasmic Reticulum


6) The core histones range between 11 and 15 kDa (1 Da = 1 g/mol). With the average amino acid size being approximately 110 Da, what is the approximate length of a post-transcriptionally modified mRNA strand used to code for H3?

a) 10,000 bases

b) 4,000 bases

c) 1,000 bases

d) 400 bases

My answers in white below:

1) C
2) C
3) D
4) C
5) C
6) D

 

[Entadus]

The question asks where are HISTONES made, not the proteins like H3. So I would say the histones are made in the nucleus (since they must incorporate DNA)

Also, pretty sure all transcription occurs in the nucleus. The rRNA is then transported to the nucleolus. (Please correct me if I'm wrong)

 

[gettheleadout]

The question asks where are HISTONES made, not the proteins like H3. So I would say the histones are made in the nucleus (since they must incorporate DNA)

Also, pretty sure all transcription occurs in the nucleus. The rRNA is then transported to the nucleolus. (Please correct me if I'm wrong)

Ah very good catch!

And nah, rRNA is actually transcribed in the nucleolus (http://www.ncbi.nlm.nih.gov/books/NBK9939/)

 

[EphemeralRose3]

The question asks where are HISTONES made, not the proteins like H3. So I would say the histones are made in the nucleus (since they must incorporate DNA)

Really making me doubt myself. lmao.

 

[Albein]

Questions for the GTLO "Passage":

1) Histones are proteins that bind to DNA through ionic interactions. Histone residues responsible for bonding to the DNA are most likely to be:

a) Histamine

b) Glutamate

c) Lysine

d) Glycine


2) Core histones involve histone proteins H2a, H2b, H3 and H4. Two each of these proteins complex to form an octamer at the center of each nucleosome. The octamer is an example of:

a) Prosthetic Groups

b) Tertiary Structure

c) Quaternary Structure

d) Nucleophilic Attraction


3) Histone charges that enable binding to DNA are neutralized by the addition of an acetyl group. The enzyme and cofactor responsible for this reaction are, respectively:

a) Histone acetyl kinase, B6

b) Histone acetyl kinase, Acetyl CoA

c) Histone acetyl transferase, B6

d) Histone acetyl transferase, Acetyl CoA


4) Histones are made in the:

a) Nucleus

b) Histosome

c) Cytoplasm

d) Nucleolus


5) Transcription of rRNA takes place in:

a) Ribosomes

b) Nucleoplasm

c) Nucleolus

d) Rough Endoplasmic Reticulum


6) The core histones range between 11 and 15 kDa (1 Da = 1 g/mol). With the average amino acid size being approximately 110 Da, what is the approximate length of a post-transcriptionally modified mRNA strand used to code for H3?

a) 10,000 bases

b) 4,000 bases

c) 1,000 bases

d) 400 bases

Should I be worried I couldn't answer half of these?

 

[Captain Sisko]

Don't worry about it, I missed #4 myself, per the above. Very, very good catch! No one's hit a perfect score yet. I've a meeting, I'll bbl

 

[Entadus]

Guys I could be wrong on both counts. It looks like Histone monomers like H3 combine to make Histones, which when added to DNA make Nucleosomes.

I wonder if the monomers are transported to the nucleus before or after assembly to become quaternary histones?

 

[gettheleadout]

Should I be worried I couldn't answer half of these?

For #1 you have to have the non-polar, polar, and charged groups of amino acids memorized (you should.

#2 You should be able to answer.

#3 You should be able to deduce from the enzyme names given and the typical function of acetyl CoA. I have no idea what B6 refers to if not the vitamin.

#4 Is tricky as Entadus pointed out, but you should know that nonsecretory proteins are translated by free ribosomes in the cytosol.

#5 and #6 you should be able to answer.

 

[EphemeralRose3]

Guys I could be wrong on both counts. It looks like Histone monomers like H3 combine to make Histones, which when added to DNA make Nucleosomes.

I wonder if the monomers are transported to the nucleus before or after assembly to become quaternary histones?

That's what I exactly what I was wondering.

 

[Captain Sisko]

That's what I exactly what I was wondering.

That was awesome quick meeting.

In perusing google before posting the questions I did come across an abstract that said individual histone proteins like h2 etc undergo nuclear import so I assume they're assembled inside.

The last problem is a little tricky. Think about translation, as a hint.

 

[Entadus]

That was awesome quick meeting.

In perusing google before posting the questions I did come across an abstract that said individual histone proteins like h2 etc undergo nuclear import so I assume they're assembled inside.

The last problem is a little tricky. Think about translation, as a hint.

That makes a lot of sense, I'm glad my instincts were good 🙂

Thanks for making the questions, Sisko! What a great idea.

 

[Captain Sisko]

For #1 you have to have the non-polar, polar, and charged groups of amino acids memorized (you should.

#2 You should be able to answer.

#3 You should be able to deduce from the enzyme names given and the typical function of acetyl CoA. I have no idea what B6 refers to if not the vitamin.

#4 Is tricky as Entadus pointed out, but you should know that nonsecretory proteins are translated by free ribosomes in the cytosol.

#5 and #6 you should be able to answer.

B6 does indeed refer to the vitamin. It's a cofactor in transamination and decarboxylation reactions, among others. You can rule it out because neither a lysine nor arginine residue lends itself to transamination, and the stem specifically asks for an acetyl addition.

 

[Dark Ace]

Someone want to explain #6 for me? 😳

 

[gettheleadout]

Someone want to explain #6 for me? 😳

11 to 15 kDa gives about 13 kDa as an average. Using 110 Da per amino acid as a conversion factor, we get a little over 100 as the number of amino acids. Since we're looking at processed mRNA, we know that introns are gone, and all remaining bases are codons for the polypeptide. 3 bases per amino acid as a conversion factor gives us about 300 bases, but we rounded down with the 110 average, so a little more. 400 is closest. Bam.

 

[EphemeralRose3]

11 to 15 kDa gives about 13 kDa as an average. Using 110 Da per amino acid as a conversion factor, we get a little over 100 as the number of amino acids. Since we're looking at processed mRNA, we know that introns are gone, and all remaining bases are codons for the polypeptide. 3 bases per amino acid as a conversion factor gives us about 300 bases, but we rounded down with the 110 average, so a little more. 400 is closest. Bam.

I second that! 🙂

 

[Captain Sisko]

Histones are officially the 3/23 groups new dead horse. I wonder what tomorrows passage will be about...

Great job all 🙂

 

[Dark Ace]

11 to 15 kDa gives about 13 kDa as an average. Using 110 Da per amino acid as a conversion factor, we get a little over 100 as the number of amino acids. Since we're looking at processed mRNA, we know that introns are gone, and all remaining bases are codons for the polypeptide. 3 bases per amino acid as a conversion factor gives us about 300 bases, but we rounded down with the 110 average, so a little more. 400 is closest. Bam.

gotcha 😉

 

[whoknows87]

Anyone using any apps to review here and there? I have MCAT once a day , and the questions are pretty good, if I covered the topic I can get it right or at least narrow it down, if I didn't cover it I'll just guess and read the brief explanation , there is also another app for Physics And Gen Chem Via BrainScape? anyone using/used those?

 

[gettheleadout]

Just flashcards on Anki. Haven't bought the $25 mobile app component though.

 

[Jr MD]

Awwwww man missed todays discussion...:/ stupid classes lol

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[gettheleadout]

Awwwww man missed todays discussion...:/ stupid classes lol

Sent from my T-Mobile myTouch Q using SDN Mobile

Lol I was in class while I was responding. Prof was rambling...

 

[Albein]

For #1 you have to have the non-polar, polar, and charged groups of amino acids memorized (you should.

#2 You should be able to answer.

#3 You should be able to deduce from the enzyme names given and the typical function of acetyl CoA. I have no idea what B6 refers to if not the vitamin.

#4 Is tricky as Entadus pointed out, but you should know that nonsecretory proteins are translated by free ribosomes in the cytosol.

#5 and #6 you should be able to answer.

yeah i was able to narrow most of them down and answered a few, but i clearly need to do better.

 

[whoknows87]

Crap man I'm starting to freak out about 67 days left or so and still have a bunch of content review left using TBR, this can't be good.............

 

[Jr MD]

Quick question: In reading the acids and bases chapter I'm a bit confused. The concentration of an acid or base does not affect the strength of the acid or base just the pH correct? So if i had 3.0 M HCl and .05 M HCl the more concentrated one would have a lower pH but the strengths would
be the same?? Thanks again!

 

[gettheleadout]

Quick question: In reading the acids and bases chapter I'm a bit confused. The concentration of an acid or base does not affect the strength of the acid or base just the pH correct? So if i had 3.0 M HCl and .05 M HCl the more concentrated one would have a lower pH but the strengths would
be the same?? Thanks again!

Precisely. Acid strength is a function of molecular structure or ionic properties, and is expressed mathematically in the acid's Ka. The Ka holds constant (given constant temperature) regardless of concentration because it is a ratio.

 

[EphemeralRose3]

Quick question: In reading the acids and bases chapter I'm a bit confused. The concentration of an acid or base does not affect the strength of the acid or base just the pH correct? So if i had 3.0 M HCl and .05 M HCl the more concentrated one would have a lower pH but the strengths would
be the same?? Thanks again!

The strength of an acid or base primarily depends on how well the compound dissociates in an aqueous solution at a given temperature (Ka/Kb values), and not the pH.

 

[gettheleadout]

The strength of an acid or base primarily depends on how well the compound dissociates in an aqueous solution at a given temperature (Ka/Kb values), and not the pH.

This is a bit misleading, actually. I'll explain why in tomorrow's fact! 😉

What Jr wants to know though is that changing an acid's concentration doesn't change its strength, though it does change the pH of the solution.

 

[Albein]

Precisely. Acid strength is a function of molecular structure or ionic properties, and is expressed mathematically in the acid's Ka. The Ka holds constant (given constant temperature) regardless of concentration because it is a ratio.

Just to add on to what gettheleadout said. This one like stuck with me from that chapter, "a highly concentrated weak acid may have a lower pH than a strong acid in low concentration." So while the strong acid in low concentration would may have a higher pH in this case, it is still a stronger acid because of its structure and as a result, a much higher Ka.

 

[Jr MD]

Just to add on to what gettheleadout said. This one like stuck with me from that chapter, "a highly concentrated weak acid may have a lower pH than a strong acid in low concentration." So while the strong acid in low concentration would may have a higher pH in this case, it is still a stronger acid because of its structure and as a result, a much higher Ka.

Ahhhhh i see...so basically the Ka is the main determinant of acid strength and regardless of the pH the acid strength is fixed. Sound about right?

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[gettheleadout]

Ahhhhh i see...so basically the Ka is the main determinant of acid strength and regardless of the pH the acid strength is fixed. Sound about right?

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Ka is a measure of the acid strength, the determinant is the structure of the acid. But yes, all that matters for acid strength is the Ka. pH is a function of both Ka and concentration.

 

[Jr MD]

Ka is a measure of the acid strength, the determinant is the structure of the acid. But yes, all that matters for acid strength is the Ka. pH is a function of both Ka and concentration.

Man i love you guys lol

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[Albein]

Ahhhhh i see...so basically the Ka is the main determinant of acid strength and regardless of the pH the acid strength is fixed. Sound about right?

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He ^ basically covered it. Strong acids dissociate fully in water and therefore have a higher Ka than weaker acids. And I guess from what ^ said, the Ka is based on the structure and how willing the acid is to donate a proton or accept a pair of electrons.

 

[Albein]

Also, anyone feel free to correct me if I'm wrong. This, in my opinion, is the best way to learn.

 

[NuttyEngDude]

hmm looks like i missed a lot of posts today 😀

 

[gettheleadout]

He ^ basically covered it. Strong acids dissociate fully in water and therefore have a higher Ka than weaker acids. And I guess from what ^ said, the Ka is based on the structure and how willing the acid is to donate a proton or accept a pair of electrons.

In a sense this is what all acid-base reactivity is based on, but the Ka is determined experimentally through titration, and is directly "based on" (I can't think of a more specific way to say this) observed concentrations of ions at equilibrium.

I like to think about this sort of abstractly; these numbers we assign to things, such as pH and Ka, are just constructs we've created to describe chemical reactions. In reality, the only thing happening is making and breaking of bonds and release/absorption of energy between different molecules, ions, and particles. The only physical differences between the players in these interactions, in the absence of our mathematical description of them, are their atomic composition and arrangement.

 

[Jr MD]

Hey gtlo you told me once that you had a nice trick for logs. Care to share?? Doing pH stuff lol

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[gettheleadout]

Hey gtlo you told me once that you had a nice trick for logs. Care to share?? Doing pH stuff lol

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Well I have several strategies that take longer to explain than I have right now, but I'll give you this to start:

And read this post.

 

[NuttyEngDude]

Cheaper, old sport!

Go on eBay, you can purchase a 6 month access for $100. Just search for gs mcat.

wow thanks a lot! I am going to make a call when i get 75% through content review, i have a fair amount of tests remaining so I need to fit them into my schedule, i have a scheudle but it's pretty barebones after content review.

I'm in the same boat as you my friend. I make very little progress in terms of catching up. Hopefully some of these chapters are a little shorter and I can get through 2 a day.

it's rough, i'm so glad i didnt take more classes as i was tempted to do a few weeks ago.. hehe

For those following SN2's study schedule, I'm having trouble deciding on something. I purchased the EK set during my first go around with this test and did only a few chapters and then took a PR course. I've been following the schedule in every aspect except for the Bio Part; I've only been using BR bio for content review and passages. Are there any suggestions for how I can take the end of chapter practice exams with the EK? My biology has been very hit or miss and I feel like I'm forgetting a lot of it as I move on. Thanks and happy studying (if there was such a thing).

i'm pretty sure there's a post with EK-TBR chapters lined up, how about htis one:
http://forums.studentdoctor.net/showpost.php?p=8092170&postcount=3

First day of class..ugghh...woke up at 6 to start studying...I'm pooped...

hehe yep. i am trying to get into the early morning routine since my mcat is early morning........ so... all my classes are early too, i get up at 7ish.

Anyone using any apps to review here and there? I have MCAT once a day , and the questions are pretty good, if I covered the topic I can get it right or at least narrow it down, if I didn't cover it I'll just guess and read the brief explanation , there is also another app for Physics And Gen Chem Via BrainScape? anyone using/used those?

Just flashcards on Anki. Haven't bought the $25 mobile app component though.

if there is something good i'd be interested but i havent been convinced of anything good yet.


---------the captain sisko questions---------

Thank you Captain Sisko for posting these.

I answered:

1.a. histamine ...is + charged? i need to memorize these 😛
2. c. quaternary structure
3. b?
4. c?
5. c. Nucleolus
6. c? assuming 11-15,000 / 110, but no idea. bleh i should have thought about it more.

and the right answers are:
1. C -- lysine
2. C -- Quaternary Structure
3. D? -- histone acetyl transferase, acetyl CoA
4. A? -- Nucleus (substituent proteins that make up the histones are made in the cytoplasm?)
5. C -- Nucleolus
6. D -- 400 bases

right?

 

[NuttyEngDude]

Well I have several strategies that take longer to explain than I have right now, but I'll give you this to start:

And read this post.

hmmm... do you use the TBR method for logs?

right now i'm sort of just memorize what log 2 and log 3 are then estimating based on that but i'm not adding it up like how TBR suggests.