Two parts of AMCAS practice I am ******ED ON please help!!! Chem and BIO

[christian15213]

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Ok first... this was a Question on the 7 AMCAS TEST... Not a question but a definition you need to know any one guess what this is??? I was LMAO when I found this on wiki.

Ok, back to the serious stuff.

Something that keeps coming up is Cell fate determination. I was wondering if anyone can come up with a good consice explanation of what it is and what we need to know for example. What exactly does this quote from wiki mean and how should I think to apply it...

. In contrast, determination refers to when cells are irreversibly committed to a particular fate. The state of commitment of a cell is also known as its developmental potential. When the developmental potential is less than or equal to the developmental fate, the cell is exhibiting mosaic behavior. When the developmental potential is greater than the developmental fate, the cell is exhibiting regulative behavior.

Next, Chemistry through a couple things my way I had some trouble with...

The question asked for the pure molarity of a molecule. I think it was Cd or something but the density was .791. now, with that said. and the molecule have a MW of 58... How do I come up with answer. The solution was telling me to take the density and multiply it by 1000 ml/L of solution and then multiply 1mol / 58g ... I wasn't following this with the reasoning of taking the density and multiplying it times the 1L... I believe it comes from something regarding the fact it is asking for the "pure substance."

 

[sehnsucht]

the way i understand the wiki definition is this:

if a cell's potential is greater than its fate to become a specific type of cell, it displays regulatory behavior because the resulting cell population will not be all one type; you are regulating its development into one cell type by giving it chance to become other cell types. this is analogous to saying that somone has the potential to become something great - in saying that about somebody, you are implying that they may go on to do something influential in life but, at the same time, since it is a potential to do something it is just as likely that they may not.

if a cell's potential is less than or equal to its fate, then a cell displays mosaic behavior because the resulting cell population is more likely to be directed to develop into a specific cell type. think about a stone or tile mosaic piece of art - the entire painting is made out of small pieces of different colored tile or stone assembled to make up a picture. they may all be different sizes and colors but they are all made of the same material: stone or tile.

as far as the chem stuff is concerned, density is a measure of mass/ volume so by taking the density of X, which in your question is 0.791, you can play around with the equation to figure out how many moles is in a given volume of solution using: density (volume) = mass. once you know the mass, you can plug that into an equation to figure out how much of Cd you have in a compound with a total MW and figure out its exact molar amount.

 

[christian15213]

the way i understand the wiki definition is this:

if a cell's potential is greater than its fate to become a specific type of cell, it displays regulatory behavior because the resulting cell population will not be all one type; you are regulating its development into one cell type by giving it chance to become other cell types. this is analogous to saying that somone has the potential to become something great - in saying that about somebody, you are implying that they may go on to do something influential in life but, at the same time, since it is a potential to do something it is just as likely that they may not.

if a cell's potential is less than or equal to its fate, then a cell displays mosaic behavior because the resulting cell population is more likely to be directed to develop into a specific cell type. think about a stone or tile mosaic piece of art - the entire painting is made out of small pieces of different colored tile or stone assembled to make up a picture. they may all be different sizes and colors but they are all made of the same material: stone or tile.

Ok, from what your saying and because time is limited. Potential means. could be anything at anygiven time? It has the potential for an arm or the potential for an ear. See, this is where I am confused but I am trying to grasp it. Now, the fate is something that we would describe as? what truly happens or what it will become?

For some reason the second part seems easier. If the cell's potential is less than or equal to its fate than Fate wins... so what ever the "fate" of that cell is then that is what it will become. I.e. an Arm, a Leg or whatever. See why I am having such a time trying to grasp this out?

Ok, See one thing from humans as well is that we have blastopores, now, from what I understand is that up until the 8 cell stage our cells are totipotent. Meaning, that they could become anything... To me the 8 cell stage and less they are regulatory style and there potential is greater than their fate.

Now, past the 8 cell stage... Lets say the blastopore, the cells have less potential than their fate meaning they are going to an arm or leg and nothing else... they are now determinate.... ???? <<<< Am I getting it here???

Ok, I guess lastly, because this is something that comes up a lot on the MCAT... How are we sure that we are not in the 8 cell stage and perhaps into the blastopore stage??/ because to me we exhibit both properites at one time or another. Primarily the past 8 cell mosaic stage but nevertheless we exhibit both... PLEASE CORRECT ME WHERE I AM WRONG...

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For the chemistry I figured it out... Easy as pie... If they give you the density of any substance or molecule... just * it by a 1000 and divide by the Molecular mass for that PURE substance... i.e. Hg would be 13 density *1000 = 13000 / MW of Hg... Water = 1 *1000 / 18 = 55.5 acetone = .791 *1000 / 58 = 13.54...

Got it Make life simple... Still need your help for the top part of Bio though.

 

[sehnsucht]

Ok, from what your saying and because time is limited. Potential means. could be anything at anygiven time? It has the potential for an arm or the potential for an ear. See, this is where I am confused but I am trying to grasp it. Now, the fate is something that we would describe as? what truly happens or what it will become?

yep. potential would mean that the cell could become anything. if you've worked with stem cells, full potential would be what totipotent cells represent...they give rise to all the cells in an organism.

For some reason the second part seems easier. If the cell's potential is less than or equal to its fate than Fate wins... so what ever the "fate" of that cell is then that is what it will become. I.e. an Arm, a Leg or whatever. See why I am having such a time trying to grasp this out?

not sure but it is a tricky concept that can easily throw one off.

Ok, See one thing from humans as well is that we have blastopores, now, from what I understand is that up until the 8 cell stage our cells are totipotent. Meaning, that they could become anything... To me the 8 cell stage and less they are regulatory style and there potential is greater than their fate.

Now, past the 8 cell stage... Lets say the blastopore, the cells have less potential than their fate meaning they are going to an arm or leg and nothing else... they are now determinate.... ???? <<<< Am I getting it here???

Ok, I guess lastly, because this is something that comes up a lot on the MCAT... How are we sure that we are not in the 8 cell stage and perhaps into the blastopore stage??/ because to me we exhibit both properites at one time or another. Primarily the past 8 cell mosaic stage but nevertheless we exhibit both... PLEASE CORRECT ME WHERE I AM WRONG...

the heirarchy for stem cells is as follows: totipotent>pluripotent>multipotent>terminally differentiated. You are correct in saying that past the 8 cell stage, cells are largely pluripotent. Pluripotent cells still have some potential since they give rise to most cells in the body but can still be coaxed in culture to differentiate into a desired cell type. However, they do not have the total potential that totipotent cells possess. As such, it would be more accurate to say that pluripotent cells are determinate to an extent since they have less potential than their totipotent counterpart.

Determining a cell's tendency to differentiate when comparing 2 cell stages is tough. I work with stem cells and coaxing cells to differentiate predictably is difficult even though the cells are pluripotent. There are many things that factor into differentiation and I think the themes are too broad to be addressed in a time limited test setting. If a comparison of differentiation is presented on the MCAT, it would have to be contextualized in a passage that will show one cell line to have less potential than the other. Sorry I can't offer a better answer.

 

[christian15213]

yep. potential would mean that the cell could become anything. if you've worked with stem cells, full potential would be what totipotent cells represent...they give rise to all the cells in an organism.

not sure but it is a tricky concept that can easily throw one off.



the heirarchy for stem cells is as follows: totipotent>pluripotent>multipotent>terminally differentiated. You are correct in saying that past the 8 cell stage, cells are largely pluripotent. Pluripotent cells still have some potential since they give rise to most cells in the body but can still be coaxed in culture to differentiate into a desired cell type. However, they do not have the total potential that totipotent cells possess. As such, it would be more accurate to say that pluripotent cells are determinate to an extent since they have less potential than their totipotent counterpart.

Determining a cell's tendency to differentiate when comparing 2 cell stages is tough. I work with stem cells and coaxing cells to differentiate predictably is difficult even though the cells are pluripotent. There are many things that factor into differentiation and I think the themes are too broad to be addressed in a time limited test setting. If a comparison of differentiation is presented on the MCAT, it would have to be contextualized in a passage that will show one cell line to have less potential than the other. Sorry I can't offer a better answer.

OK, no you are sure helping because this is something that keeps coming up and I want to be prepared.

As well, The mcat passage practice 7... Had this concept all over it. As well, they stressed cell signaling and thus must be exactly what you are talking about "coaxing cells" to become what you want them to be.

Got anything for Immune system.

 

[christian15213]

If anyone has a quick story for the immune system it would be a great help... I am developing one for the blood...

 

[christian15213]

Oh and this is an easy help for a negative feedback question


Think of negative feedback like this... IT IS SO EASY> > > AFTER YOU THINK of it this way.

All you have to do for negative feed back is ask yourself... "What would the body do to fix this situation." Turn it on or turn it off. If it is turn it on that is positive feedback... If it is turn it off that is negative feed back... REMEMBER... "WHAT WOULD THE BODY DO TO FIX THIS SITUATION." 😛

 

[RSAgator]

Oh and this is an easy help for a negative feedback question


Think of negative feedback like this... IT IS SO EASY> > > AFTER YOU THINK of it this way.

All you have to do for negative feed back is ask yourself... "What would the body do to fix this situation." Turn it on or turn it off. If it is turn it on that is positive feedback... If it is turn it off that is negative feed back... REMEMBER... "WHAT WOULD THE BODY DO TO FIX THIS SITUATION." 😛

that's not a very good way of thinking about it...there are mechanisms of negative feedback that involve the body turning things on as well as turning things off. Negative feedback doesn't necessarily mean that something's going to turn off, it means that a certain action causes an opposing response which could be turning something on (opening up your capillaries to regulate temperature) or turning something off (closing your capillaries to regulate temperature).

edit: oh and positive feedback acts completely differently. It involves more of a cascading effect until completion such as in blood clotting or in pregnancy. Once a clot starts positive feedback causes more and more platelets to clot.

 

[christian15213]

that's not a very good way of thinking about it...there are mechanisms of negative feedback that involve the body turning things on as well as turning things off. Negative feedback doesn't necessarily mean that something's going to turn off, it means that a certain action causes an opposing response which could be turning something on (opening up your capillaries to regulate temperature) or turning something off (closing your capillaries to regulate temperature).

edit: oh and positive feedback acts completely differently. It involves more of a cascading effect until completion such as in blood clotting or in pregnancy. Once a clot starts positive feedback causes more and more platelets to clot.

I completely agree with everything about the positive feedback... But in general for the MCAT... what would the body do to fix this situation... WILL always answer the question... 👍