Organismal Biology/Physiology Thread

[QofQuimica]

All users may post questions about MCAT, DAT, OAT, or PCAT organismal biology (anatomy, physiology, development, embryology, and evolution) here. Cellular bio, molecular bio, and biochemistry questions should be posted in the other biology thread. We will answer the questions as soon as we reasonably can. If you would like to know what biology topics appear on the MCAT, you should check the MCAT Student Manual (http://www.aamc.org/students/mcat/st...nual/start.htm)

Acceptable topics:
-general, MCAT-level biology.
-particular MCAT-level biology problems, whether your own or from study material
-what you need to know about biology for the MCAT
-how best to approach to MCAT biology passages
-how best to study MCAT biology
-how best to tackle the MCAT biological sciences section

Unacceptable topics:
-actual MCAT questions or passages, or close paraphrasings thereof
-anything you know to be beyond the scope of the MCAT

*********

If you really know your organismal biology, I can use your help. If you are willing to help answer questions on this thread, please let me know. Here are the current members of the Organismal Biology Team:

Maddscientist (thread moderator): Maddscientist is a Ph.D. student in developmental biology.

TheDarkSide: TheDarkSide has several years of experience working as a nurse. She scored 12 on the BS portion of the MCAT, and 37 overall.

Occasional moderator: Shrike. Shrike is a full-time instructor for The Princeton Review. His primary expertise is in other subjects; he knows just enough biology to have scored 12 on the BS section without ever having studied organic chemistry.

[Kussemek]

I am looking at my notes from TPR, attempt 1 and am using Audio Osmosis for attempt 2 in addition to TPR class. TPR really only emphasized 3 types of mutations (i guess you could call them 2)...those being point mutations and insertion and deletion. AudioOsmosis mentions netural, transposition, back mutation, wildtype... What are the basics we need to know about mutations? Thank you.

[LT2]

Hi-

With regards to mutations, i would assume that the three (and i would call them three, they're all pretty distinct) TPR "classes" of mutations are going to be the most common fodder for questions asked. Point mutations are single base changes and can be neutral (do not change the amino acid being coded for), missense (the amino acid being coded for is changed to another amino acid due to the point mutation) or nonsense (the amino acid being coded for is changed to a "stop" due to the point mutation). Insertions and deletions are just like the name suggests.

I am not an authority on what will or will not be on the MCAT, but you should also have an idea of the other mutations you mentioned. wild-type is not a mutation, but the natural presentation of something. a back mutation usually involves an original mutation that is reverted back by a second mutation (so the sequence goes "back" to what it was). transposition usually involves mobile dna.

Hope this helps...

[MollyMalone]

Originally Posted by Kussemek

I am looking at my notes from TPR, attempt 1 and am using Audio Osmosis for attempt 2 in addition to TPR class. TPR really only emphasized 3 types of mutations (i guess you could call them 2)...those being point mutations and insertion and deletion. AudioOsmosis mentions netural, transposition, back mutation, wildtype... What are the basics we need to know about mutations? Thank you.

Hi!

Good information given above.

According to the AAMC MCAT student manual, the following is fair game for mutation material: "random, translation error, transcription error, base substitution, inversion, addition, deletion, translocation, mispairing."

Here are my quick thoughts (skipping insertion and deletion and point mutations since you said you had those):

Wild-type mutations: a base substitution that does not result in a change of amino acid, usually no effect on phenotype (apparently some really subtle things can occur but I wouldn’t worry about it for MCAT level questions). This one is confusing because here the "wild-type" refers only to the phenotype, not to both the phenotype and the genotype as I usually hear the term used.

Neutral mutations: have no effect on function.

Back mutations: When something was once A but is now B changes “back” to A again.

Inversion mutations: when a sequence of nucleotides is reversed (DNA level), or when a sequence of genes is reversed (chromosome level).

Transposition mutations: “jumping genes” (transposons) which can cause translocation, insertion, and deletion mutations.

Translocation mutations: genes from one of a pair of homologous chromosomes separate and attach to the other chromosome in the pair. Can occur during crossing over.

Obviously, errors can occur in translation (wrong AA) and transcription (wrong base) both.

Good illustrations available at:

http://www.biology-online.org/2/8_mutations.htm

http://www.people.virginia.edu/~rjh9u/chrominv.html

Nice, concise reference about transposition (but way more than necessary information):

http://wiki.cotch.net/index.php/Transposition

I hope that was helpful!

[Kussemek]

yes, thanks for the response!

[blankguy]

What should I focus on for the nervous system and how it is organized(central, peripheral, motor, autonomy, etc...) in the area of action potential? How much detail should I know about the eyes, and ears?

[MollyMalone]

Originally Posted by blankguy

What should I focus on for the nervous system and how it is organized(central, peripheral, motor, autonomy, etc...) in the area of action potential? How much detail should I know about the eyes, and ears?

Hmmm. I'm not quite sure what you're asking in the first question. You definitely need to know all the organizational levels of the nervous system (anatomical and functional). You should know the structure of neurons. I would try to be familiar with action potentials in as much detail as you can, but the really important features are that it's a threshhold (all or nothing) effect and that it's based on the sodium-potassium pump. I would also be very familiar with the major classes of neurotransmitters.

For the eyes and ears you don't need very detailed anatomy (I don't think they'd ever ask a question about naming the bones of the ear) but you should understand the basic mechanics of vision and hearing... which you get in physics!

Hope that helps and please let me know if you want some of that clarified... it's been a long day!

[blankguy]

How much detail should I focus on the action potential? EK seems to gloss over it. In the bio course that I took, I had to learn how muscle contracts, what how it depolarizes on an already created action potential, resting potential, how it gets trasmitted thorugh a synapse (neurotransmitter).

[MollyMalone]

I'm not familiar with the EK materials but my personal position would be to know all the things you mention from your bio class. I would absolutely memorize the shape of the time/voltage curve and the direction of movement of the ions, including calcium. I would definitely be familiar with saltatory propagation and the relevant anatomy. My personal theory based on my limited experience is that the test writers are in love with neurotransmitters so I would focus on that topic quite a bit.

I would encourage you to check out the MCAT Student Manual (the link is in the first post of this thread) which goes into a lot of detail about what material AAMC thinks you need to know for the test.

Hope that helps! Good luck!

[Shrike]

Originally Posted by TheDarkSide

I would encourage you to check out the MCAT Student Manual (the link is in the first post of this thread) which goes into a lot of detail about what material AAMC thinks you need to know for the test.

Caveat: the linked document shows what students are expected to know, not the relative importance of different items. Do your homework (including in this thread) to find out what's really necessary.

As to action potentials, what's really necessary here is exactly what DarkSide said.

[blankguy]

Okay, I'm finding myself trying to get the overall idea of how certian systems like digestive, excretory and respiratory system work but I am unnerved by the fact that all the terminology in the EK book is what I gloss over. Should I memorize the terms in conjunction with getting the gist of the systems?

[jmugele]

Originally Posted by blankguy

Okay, I'm finding myself trying to get the overall idea of how certian systems like digestive, excretory and respiratory system work but I am unnerved by the fact that all the terminology in the EK book is what I gloss over. Should I memorize the terms in conjunction with getting the gist of the systems?

I think it's important to know the terminology as wel as the overall functions of the system. I never used Examkrackers, so I'm not sure how they organize their material, but here's what helped me: when I was studying for the long-haul (sitting at the dinner table for 3-4 hours), I would make sure I got the gist of a system. For the details, I studied the hell out of flashcards -- I used Kaplan's which were pretty good, but I also made some of my own as I was studying. I would write down any significant facts or terms that I ran across when I was reading the material. I would do flashcards while I was eating, driving, on the toilet -- anywhere. After a while, the details sunk in.

[TheGuy2000]

One more question guys, this one about circulation and the MCAT. In tracing the blood around the heart and to the lungs I found Kaplan's explanation to be well...krappy. The left side I think pumps the deoxygenated blood, I know there's a systole and a diastole which are the lub/dub. Blood from the lower body is from the inferior vena cava, upper superior. But I'm just having trouble piecing it all. Can someone give me a good rundown for the MCAT?

[Nitya2284]

Can anyone post how the digestive, excretory and reproductive systems work and what we need to know for the MCAT?

[Nitya2284]

Originally Posted by Nitya2284

Can anyone post how the digestive, excretory and reproductive systems work and what we need to know for the MCAT?

wrong section..my bad..this should be in the biology section..sorry

[Nitya2284]

Can anyone post how the digestive, excretory and reproductive systems work and what we need to know for the MCAT?

[Shrike]

Originally Posted by TheGuy2000

...I know there's a systole and a diastole which are the lub/dub.

The rest of this qestion's been addressed, but I thought someone better mention: The "lub" and "dub" are valve closures, not systole and disatole. Specifically, the "lub" is the closure of the two atrioventicular (AV) valves, the bicuspid and tricuspid, at the begining of systole; the "dub" is the closure of the semilunal valves, the ones between the ventricles and the arteries, at the end of systole.

Apologies if this answer has already been given, too; I missed it.

[Nutmeg]

Not to be a thread Nazi, but perhaps issues of blood vessels would be more appropriate for the organismal biology thread...

[scooter31]

I was wondering if Shrike's method for attacking PS passages applies to Bio-- is it a good to skim the passage at most and focus on the reactions, figures, graphs, equations, etc then dig into the questions? I could see where certain subjects (CAC, maybe certain physio passages) this would be great, but what about genetics passages? Any thoughts?

Aside to Shrike: I used your method for PS, and went from 9's and 10's to 12's on my practice exams. Thanks for making my toughest section my strongest!

[Shrike]

There is no perfect answer to the question about how to attack a bio passage, but what I advise is very similar to my physics approach. Possible differences:

• It may be acceptable to skim the entire passage, or skim until you get to obviously detailed information, because biology passages resemble verbal reasoning more than do physics passages.
  
  
• Because tables of experimental values are likely to be of values you understand (in contrast to physics, where that's far from guaranteed), it may make sense to look briefly at tabular data and at graphs for general trends.

These things said, they're not what I advise (nor what I personally do) -- I advise the same approach as I do for physics passages (see link above). No reading the passage; just examine the figures, graphs, and tables. At most, skim the text. Total time prior to questions should be under 45 seconds. Then, on to the questions, on which you can now spend the needed time.

[MollyMalone]

I always at least skim, but time has never been an issue for me and I honestly think you'd probably be fine doing it Shrike's way.

[scooter31]

Thanks for the input, Mods-

As can be gathered form my previous post, I am a big fan of the technique, and would hope to see similar trends in Bio improvent using it. Just wanted to make sure that I wasnt missing anything by applying the method in Bio passages

[medstu2006]

I always get confused about this issue. Can someone please sum it up and help me see the light?

[MollyMalone]

Originally Posted by medstu2006

I always get confused about this issue. Can someone please sum it up and help me see the light?

Important things to know about acid/base balance in the human body FOR THE MCAT:
(i.e., this is not meant to be a complete discourse on the subject)

The buffer system you need to know: HCO3-/CO2 (think HCO3- = base and CO2 = acid)

Chemical equation: H+ + HCO3- = H2CO3 = CO2 + H2O (imagine the equilibria arrows)

The lungs independently control CO2 (fast response – minutes to hours) while the kidneys independently control HCO3- (slow response – hours to days).

Physiologic pH: 7.4

When the pH goes out of whack, the body has a few different ways to deal with it: buffering, compensation, and correction. Buffering is automatic and instantaneous – it’s a function of the chemistry shown above. When the challenge to the buffering system is too great and the pH becomes materially affected, chemoreceptors pick up this signal encourage the appropriate system to take action. The response depends on whether it is a metabolic problem (HCO3- too high or low) or a respiratory problem (CO2 too high or low). The kidneys adjust to compensate for respiratory problems (can do this by a variety of mechanisms but basically you just need to know that it affects HCO3- levels) while the lungs adjust the CO2 level by hyper- or hypoventilation to compensate for metabolic disorders. These compensatory mechanisms function best as a temporary stopgap (minutes to days) until the body can manage to correct the underlying reason for the acid/base imbalance. Of course, sometimes the problem is not correctable and people wind up living in a chronically compensated state.

Here’s a handy list of the four main problems and what happens with them:

Respiratory acidosis – caused by lung problems. Levels of CO2 are too high, causing pH to drop. The kidneys respond by increasing levels of HCO3-.

Respiratory alkalosis – caused by lung problems. Levels of CO2 are too low, causing pH to rise. The kidneys respond by decreasing levels of HCO3-.

Metabolic acidosis – not caused by lungs. Levels of HCO3- are too low, causing pH to drop. The lungs respond by decreasing levels of CO2 (hyperventilation).

Metabolic alkalosis – not caused by lungs. Levels of HCO3- are too high, causing pH to rise. The lungs respond by increasing levels of CO2 (hypoventilation).

Just for fun, some causes of each (not an exhaustive list):

Respiratory acidosis: pulmonary embolism, cardiac arrest, pneumonia, COPD, airway obstruction – you get the drift. Things that impair the lungs’ ability to move air or do gas exchange.

Respiratory alkalosis: pain, fever, things that cause respiratory rate and depth to increase.

Metabolic acidosis: diarrhea (loss of base via GI tract), ketoacidosis (from diabetes), lactic acid build-up, several drugs.

Metabolic alkalosis: vomiting (loss of acid via GI tract), occasionally gain of base (saw this once in a lady who drank multiple bottles of Maalox)

I hope that was helpful. As always, if I made an error or if someone has something to add, please feel free to comment.

[myfavred]

Could someone please explain to me the female gametes from the time of her birth till ovulation. I was under the impression that at the time of birth the gametes are at Anaphase I but I recently read that it is at Meiosis I. So which one is it? Thanks

[travelbug73]

Originally Posted by myfavred

Could someone please explain to me the female gametes from the time of her birth till ovulation. I was under the impression that at the time of birth the gametes are at Anaphase I but I recently read that it is at Meiosis I. So which one is it? Thanks

The primary oocytes formed at birth (no more will be made, ever) start meiosis I and are arrested in Prophase I until puberty, during which time many of the primary oocytes regress. Once puberty starts, ONE primary oocyte, every month, will complete meiosis I, resulting in the formation of a secondary oocyte and a polar body. The secondary oocyte starts meiosis II and again stops, this time at Metaphase II.
During ovulation, the secondary oocyte, released into the fallopian tube, will complete meiosis II and form the mature egg (ovum) and another polar body, if and only if there is a sperm available. If there is no sperm available the secondary oocyte will be discharged during menstruation without underoging meiosis II.
The first polar body also divides resulting in 2 more polar bodies. Therefore, at the end of meiosis II, there should be at least 2 and maybe 3 polar bodies (if there is fertilization).
In short, the primary oocyte is at Prophase I until puberty.

Hope this helps.

[myfavred]

Originally Posted by travelbug73

The primary oocytes formed at birth (no more will be made, ever) start meiosis I and are arrested in Prophase I until puberty, during which time many of the primary oocytes regress. Once puberty starts, ONE primary oocyte, every month, will complete meiosis I, resulting in the formation of a secondary oocyte and a polar body. The secondary oocyte starts meiosis II and again stops, this time at Metaphase II.
During ovulation, the secondary oocyte, released into the fallopian tube, will complete meiosis II and form the mature egg (ovum) and another polar body, if and only if there is a sperm available. If there is no sperm available the secondary oocyte will be discharged during menstruation without underoging meiosis II.
The first polar body also divides resulting in 2 more polar bodies. Therefore, at the end of meiosis II, there should be at least 2 and maybe 3 polar bodies (if there is fertilization).
In short, the primary oocyte is at Prophase I until puberty.

Hope this helps.

Thank you so much it really helped.

[Abe]

im having trouble with the menstruation cycle. Im confused as to what everything comes from, ovary produces estrogen and progestrone, they thicken the endometrium together. But whats a follicle? and where does an ovum come from? The follicle or the ovary? Im just not getting the big picture, i think i got the hormones part down, LH and FSH surge because of estrogen and gnrh, progestrone+estrogen inhibits gnrh LH FSH.
oh and where does the corpus luteum fit into this picture?

[Nutmeg]

Originally Posted by Abe

im having trouble with the menstruation cycle. Im confused as to what everything comes from, ovary produces estrogen and progestrone, they thicken the endometrium together. But whats a follicle? and where does an ovum come from? The follicle or the ovary? Im just not getting the big picture, i think i got the hormones part down, LH and FSH surge because of estrogen and gnrh, progestrone+estrogen inhibits gnrh LH FSH.
oh and where does the corpus luteum fit into this picture?

The ova in the ovary are associated with the follicles; basically, the follicle is a subdivision of the ovary, with each follicle containing one ovum. The ova (plural of ovum) are all part of the ovary from early in life (at least, that is what I've originally been taught, but this has recently been found to not be the case in mice), with a finite number of ova that slowly mature one-by-one in the sexually mature female.

As the FSH stimulates the maturation of the follicles, eventually one will generally dominate, and it will release hormones that tell the pituitary gland that a cell is mature, and that inhibit the growth of other follicles, to make only a single mature egg cell at a time. When the follicle ruptures, the remaining scar tissue is referred to as the corpus luteum, and this will continue to release hormones (progesterone) to trigger the thickening of the endometrial lining in expectation of zygote implanting.

[Lindyhopper]

Originally Posted by travelbug73

. . During ovulation, the secondary oocyte, released into the fallopian tube, will complete meiosis II and form the mature egg (ovum) and another polar body, if and only if there is a sperm available. If there is no sperm available the secondary oocyte will be discharged during menstruation without underoging meiosis II.
The first polar body also divides resulting in 2 more polar bodies. Therefore, at the end of meiosis II, there should be at least 2 and maybe 3 polar bodies (if there is fertilization).
In short, the primary oocyte is at Prophase I until puberty.
. . .

I'm pretty sure Travelbug is accurate.

[Nutmeg]

Originally Posted by Lindyhopper

I'm pretty sure Travelbug is accurate.

My bad. My bio teachers always referred to the primary oocyte as an ovum, regardless of stage of maturation.

[medstu2006]

Could anyone please describe fetal circulation in detail?

[stoleyerscrubz]

I finished studying all of EK and I have the basics down for the most part but there are a number of things mentioned in the AAMC MCAT Topic List that were not covered in EK materials and I did not go over them during my 2 semesters of bio this past year. Could you comment on what we need to know about some of these. Thanks.

Genetics:leakage, penetrance,expressivity
meiosis and genetic variability-sex linked characteristics:cytoplasmic inheritance
meiosis and genetic variability-mutation:advantageous vs deleterious mutations

[goleafsgo]

could someone go over #ATP at different points of glycolysis & krebs that we need to know? thanks

[Lindyhopper]

The ATP count of glycolysis, Krebs cycle etc. is well covered in the biochem & cell Study Q & A thread.

[medworm]

I encounter things like Growth Factors, Intrinsic Factors and others in my readings, because they're not well explained. What are they? Proteins? Enzymes? How should I think of them?

Confused

[Chris Benoit]

Hey guys,

Where do B cells mature? I know that T cells mature in the thymus, but I can't find where B cells mature.

Thanks!

[hippocampus]

there was this dumb question in BR...


in the sliding filament model, which part has the least actin filament overlap?

so i thought "least," the ultimate least, would be "none." so of course the most non-overlap would be when it is at its longest length...

however, the answer is when it is at its second shortest length (before the optimal length), because they meant that "least" is "a little bit" overlap, not "none."

so if there is ever a question that asks "least"... should we never assume it means "none"?

[hippocampus]

in the passage, it said that "stibestrol is a crystalline NON-steroid hormone with estrogenic effects often superior to those of the strogen, estradiol"


and then have have questions about how it affects cells, etc.

since they said it was a non-steroid hormone, i thought that they meant it would act in a second messenger way. however, to my surprise, it locates to the nucleus like a regular steroid.. whattt?? why did they say it was non-steriod then? how are we suppose to know that it wont do the second messenger pathway??

this is from 4921, bio passage number 3

[CanuckAnatomist]

Originally Posted by travelbug73

...
The first polar body also divides resulting in 2 more polar bodies. Therefore, at the end of meiosis II, there should be at least 2 and maybe 3 polar bodies (if there is fertilization).
In short, the primary oocyte is at Prophase I until puberty.

I agree with everything else you said, however I believe the two polar bodies (one produced following meiosis I, and the 2nd following meiosis II) degenerate and do not divide. If you want to be picky, the 1st polar body degenerates, wherease the 2nd polar body (produced from the secondary oocyte, not the 1st polar body) is discarded.
According to Ross, Reith and Romrell's Histology (2nd ed.- the forerunner to Ross, Kaye and Pawlina) "in the human, the first polar body does not divide; therefore the fertilized egg can be recognized by the appearance of the second polar body. The polar bodies, which are not capable of further development, undergo degeneration".
Unfortunately, in the diagram on the subsequent page (pp. 656-657) it seems to suggest that the 1st polar body would divide.
My 3rd edition Moore ("The Developing Human") seems to bear this out.
I've usually taken to following text over figures in such cases, but to each his own. I haven't heard of any more recent research, and a medline search didn't reveal anything particularly exciting about 1st polar body division.

And I wouldn't give polar bodies a second thought in studying for the MCAT, except to know that the meiotic divisions are asymmetric in the female, but symmetric in the male. You won't be making calls on ovarian biopsies (unless they've come a long way in providing good images since I last saw an MCAT).

Cheers!

Kevin

[juiceman311]

Can someone please! go through the cell cycle and mark if it's N, 2N, or 4N at the respective stage? I am having a great deal of confusion and conflict, as my Kaplan book says one thing and my Bio-major friend says another which is in direct contradiction...and I believe him, but now my sister tells me that the Kaplan book is right! WTF!

Here, I'll start it for you so you can fill it in for me. Thanks in advance...

G1
S
G2
Prophase
Metaphase
Anaphase
Telophase

Same for meiosis too please (I know what's happening at each of the stages, just unclear of the genetic #s)

edit- Okay...now I think I'm just really trying to hurt myself...it's 1 cell @ 2N going into meiosis I and 2 cells @ N going into meiosis II producing 4 cells @ N?? I don't see how the genetic information is being conserved at all here....2 x N doesn't equal 4 x N?

[totalcommand]

Originally Posted by juiceman311

Can someone please! go through the cell cycle and mark if it's N, 2N, or 4N at the respective stage? I am having a great deal of confusion and conflict, as my Kaplan book says one thing and my Bio-major friend says another which is in direct contradiction...and I believe him, but now my sister tells me that the Kaplan book is right! WTF!

Here, I'll start it for you so you can fill it in for me. Thanks in advance...


Same for meiosis too please (I know what's happening at each of the stages, just unclear of the genetic #s)

edit- Okay...now I think I'm just really trying to hurt myself...it's 1 cell @ 2N going into meiosis I and 2 cells @ N going into meiosis II producing 4 cells @ N?? I don't see how the genetic information is being conserved at all here....2 x N doesn't equal 4 x N?

Ploidy is the number of basic chromosomes in a cell (in humans one chromosome from father, one from mother = 2N.).

Mitosis (Ploidy never changes):

G1 2N
S 2N
G2 2N
Prophase 2N
Metaphase 2N
Anaphase 2N (sort of)
Telophase 2N (sort of)

Meiosis (Ploidy gets halved):

G1 2N
S 2N
G2 2N
Prophase I 2N
Metaphase I 2N
Anaphase I N (sort of)
Telophase I N (sort of)

Prophase II N
Metaphase II N
Anaphase II N (sort of)
Telophase II N (sort of)

I think the answer to the second part of your question is that Mitosis and Meiosis have different separation during Anaphase.

In Mitosis, you separate the chromosomes by moving sister chromatids in opposite directions.

In Meiosis, you separate homologous chrmosomes in opposite directions. The second division will separate the chromatids of one homologue.

X = chromosome 1, x = chromosome 1 homologue.
X' = chromosome 1's sister chromatid, x' = chromosome 1 homologue's sister chromatid.

Mitosis:

(Metaphase) XX'xx' ----->>>> (Anaphase) Xx | X'x'
(All genetic information is preserved during division, thus ploidy remains 2N)

Meiosis:

(Metaphase I) XX'xx' ------->>>> (Anaphase I) XX' | xx'
(Homologues have been divided, losing half the information in Anaphase I. Thus, the ploidy becomes N)

I hope this isn't too confusing.

[CanuckAnatomist]

I would argue that after S-phase, you have twice as many chromatids, which are only duplicated chromosomes (still the same chromosome number, only with two chromatids per chromosome).

So when the sister chromatids separate in anaphase, the resulting chromosome number (N) should be 4N, because you then have 92 chromosomes still bound together in one cell, until the cleavage furrow is complete.
My take would be:
G1 (2N)
S (2N, with twice the actual DNA complement)
G2 (2N)
M: Prophase (2N), Metaphase (2N), Anaphase (4N), Telophase (4N)

following cytokinesis, you have two cells, both 2N. Therefore the chromosome number in telophase has to be 4N.

Similarly in meiosis: (for accounting purposes much like 2 successive rounds of mitosis without the intervening S-phase)

G1 (2N)
S (2N with twice the DNA complement)
G2 (2N)
Meiosis I:
Prophase I (2N)
Metaphase I (2N)
Anaphase I (4N)
Telophase I (4N)
Cytokinesis : 2 x 2N. I'll write it as (2N) (2N) to indicate two cells.
Prophase II: (2N) (2N)
Metaphase II: (2N) (2N)
Anaphase II: (N+N) (N+N) maternal and paternal chromatids segregate independently to opposite poles of the cell
Telophase II: (N+N) (N+N)
Cytokinesis: (N) (N) (N) (N)

But it is little substitute for a book. Nevertheless, there must be a 4N complement following separation of duplicated chromosomes at anaphase for mitosis. Some authors describe a duplicated chromosome complement (following S-phase) as 4N. You should understand the difference. I'm not sure what is written in the Kaplan review, haven't read it myself.

Cheers

Kevin

[speranza]

Originally Posted by hippocampus

in the passage, it said that "stibestrol is a crystalline NON-steroid hormone with estrogenic effects often superior to those of the strogen, estradiol"


and then have have questions about how it affects cells, etc.

since they said it was a non-steroid hormone, i thought that they meant it would act in a second messenger way. however, to my surprise, it locates to the nucleus like a regular steroid.. whattt?? why did they say it was non-steriod then? how are we suppose to know that it wont do the second messenger pathway??

this is from 4921, bio passage number 3

This is a tricky question. Stibestrol is probably an amino acid derivative. This type of hormone can act both like peptide and steroid hormones. Since the passage states that its effects are superior to estradiol (a steroid hormone) you can infer that it must act in the same manner as steriod hormones by entering the nucleus. So I guess the key to answering this question is knowing that there are three classes of hormones - peptide, steroid and amino acid - and that amino acid hormones can activate target cells in the same manner as the other two.

[QofQuimica]

A big bump for organismal bio.

[QofQuimica]

bumping

[Caboose]

Howdy.
The sympathetic NS uses norepinephrine to increase BP/HR + blood glucose, dialates pupils, opens up the lungs and shunts blood away from the GI. O.k., but why, oh why, would I want blood to go away from my brain and heart if I'm being chased by QofQuimica?

Caboose.

[QofQuimica]

Originally Posted by Caboose

Howdy.
The sympathetic NS uses norepinephrine to increase BP/HR + blood glucose, dialates pupils, opens up the lungs and shunts blood away from the GI. O.k., but why, oh why, would I want blood to go away from my brain and heart if I'm being chased by QofQuimica?

Caboose.

I don't think the blood goes away from your brain and heart. It goes away from your GUT, which makes sense, because if you just sit around and digest, then I'm gonna getcha.

[Caboose]

Originally Posted by QofQuimica

I don't think the blood goes away from your brain and heart. It goes away from your GUT, which makes sense, because if you just sit around and digest, then I'm gonna getcha.

Caboose found an error. It's a good thing we realized it too because I would have been toast.
Caboose.

[frany584]

I had a question about the Bohr effect. In the case of decreasing pH or increasing [CO2], hemoglobin has a decreased affinity for O2; however, how is this related to cooperativity? Does a decrease in affinity mean there is an decrease in cooperativity? Or is cooperativity and affinity inversely related? Thanks.