Biochemistry, cell biology, and genetics question thread

[Nutmeg]

All users may post questions about MCAT, DAT, OAT, or PCAT cell/molecular biology, genetics, and biochemistry here. Anatomy, physiology, development, embryology, and evolution 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/s...anual/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

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If you really know your cell/molecular 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 Cell/Molecular Biology Team:

-Nutmeg (thread moderator): My background is in neurobiology. Please note that I am nocturnal, and generally only post between the hours of 10pm and 8am PST.

I'm going to make this thread a bit different than the others, because the material covered in the BS section is a bit different. With o-chem, gen-chem, and physics, there are a number of core concepts to understand. While there is also a lot of that in the BS, there is also a great deal of specific knowledge involved in this section (relative to the others). Test questions often introduce an experimental set-up, asking for either expected results or the interpretation of results. As such, passages might relate to advanced concepts that you are not expected to know coming into the test, and that they will explain in the passages. Any familiarity that you have with these concepts will make the test easier.

While in general this forum is designed for people studying for the MCAT, I welcome any questions relating to molecular biology, even though they might be beyond the scope of the MCAT. I know some people also like to use these threads to get help on homework questions, and I welcome that, too.

-LT2: LT2 is finishing her MS in microbiology.

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[gridiron]

I have a silly defintion question. Where is the interstitial space if you're looking at a picture of a cell with basolateral, apical, and lumen labeled? My problem says that Chlorine secretion into the interstitial space and I have no idea where that is. Also, is there an opposite for interstitial i.e, extracellular space vs intracellular.

Also, what is the difference between in vitro and in vivo?

Thank you!

Interstitial fluid is one of two components of extracellular fluid. The other component is plasma. I think plasma is the same thing as interstitial fluid minus the proteins and other large substances. It is primarily the fluid for cells and tissues--in delivering wastes and materials.

 

[harrypotter]

Thank you for your response biomedengineer, but I was looking for where the interstitial space in relation to a picture of a cell.

Thanks again!

 

[pezzang]

I have a silly defintion question. Where is the interstitial space if you're looking at a picture of a cell with basolateral, apical, and lumen labeled? My problem says that Chlorine secretion into the interstitial space and I have no idea where that is. Also, is there an opposite for interstitial i.e, extracellular space vs intracellular.

Also, what is the difference between in vitro and in vivo?

Thank you!

-> Interstitial fluid is more likely to be facing basolateral surface since apical surface faces the lumen as in the case of kidney (nephron). If you read any physiology books describing the anatomy of kidney, you will see that interstitial fluid is on the basolateral side. Interstitila fluid, hence, could be extracellular fluid, and basolateral+apical sides are the surfaces separating lumen of a cell and extracellular matrix (sort of like E and B(?) of phospholipid bilayer).


QofQuimica, can you plz answer my post #148?

 

[QofQuimica]

QofQuimica, can you plz answer my post #148?

Sorry, I don't know the lymphatic system well enough to answer it. I'll PM MollyMalone and see if she can help you.

 

[MollyMalone]

Can somebody explain how lymphatic system works? I mean it seems it functions to clear up interstitial fluid and blood from infection by holding lymphocytes (WBCs). But since all blood cells stem from bone marrow, they migrate to lyphatic system after they are produced in bone marrow and become matured in thymus/bone marrow? I realize lymphatic system is an open system, which is connected to the circulatory system but I am not so keen on this part. It's connected by thoratic duct? I know the path of fat from liver to the thoratic duct and left jugular vein and finally to the heart, but what about other substances? I know this is a vague question but I would appreciate a response. Thank you!!!

The basic functions of the lymphatic system are to return interstitial fluid and substances to the circulatory system, to transport fat from the small intestine to the circulatory system, and to play a role in the immune system by hosting macrophages and lymphocytes and filtering the lymph for pathogens.

T cells mature in the thymus, B cells mature in the bone marrow. The T cell progenitors migrate to the thymus via the circulatory system, as far as I'm aware.

Lymph starts as blood plasma that's been leaked from the circulatory system and into tissues. This fluid is collected by diffusion into the lymphatic capillaries. Just like in the circulatory system, the lymph system has progressively larger vessels, with valves like veins have. The lymph system drains into the circulatory system at two points: the right lymphatic duct drains the upper right part of the body, while the thoracic duct drains the rest. These empty into the right and left subclavian veins respectively.

Lipids and fat-soluble vitamins are collected from the small intestine via the lacteals of the intestinal villi. These substances are then delivered to the circulatory system via the thoracic duct. The lymph picks up other substances from the interstitial spaces.

I hope that helps -- you're right, you were a little vague.

 

[pezzang]

The basic functions of the lymphatic system are to return interstitial fluid and substances to the circulatory system, to transport fat from the small intestine to the circulatory system, and to play a role in the immune system by hosting macrophages and lymphocytes and filtering the lymph for pathogens.

T cells mature in the thymus, B cells mature in the bone marrow. The T cell progenitors migrate to the thymus via the circulatory system, as far as I'm aware.

Lymph starts as blood plasma that's been leaked from the circulatory system and into tissues. This fluid is collected by diffusion into the lymphatic capillaries. Just like in the circulatory system, the lymph system has progressively larger vessels, with valves like veins have. The lymph system drains into the circulatory system at two points: the right lymphatic duct drains the upper right part of the body, while the thoracic duct drains the rest. These empty into the right and left subclavian veins respectively.

Lipids and fat-soluble vitamins are collected from the small intestine via the lacteals of the intestinal villi. These substances are then delivered to the circulatory system via the thoracic duct. The lymph picks up other substances from the interstitial spaces.

I hope that helps -- you're right, you were a little vague.

Thanks, MollyMalone (and QofQuimica for letting her know). It's a lot clear in my mind now. However, I am just a bit confused about the presence of leukocytes in circulatory system and lymphatic system. Do both systems always have all leukocytes (lymphocytes, monocytes, megakaryotes, and other granular leukocytes such as neutrophils, basophils and eosinophils)? I realize all blood cells arise/differentiate from the bone marrow but where do granular leukocytes mature?
Also, if circulatory system contains leukocytes, what's the point of having a lymphatic system? I mean leukocyts in circulatory system will eliminate infecitons and other infective substances. Is it because circulatory sytem can't eliminate infections in interstitial fluid so lymphatic is present mainly for that purpose? Your explanation of the various purposes of lymphatic system is very concise and to the point, but I am just curious why we need lymphatic system if blood carries leukocytes (Does blood only carry T/B-cells+macrophages, or does it carry complete set of leukocytes?). Do lymphatic and circulatory system carry different leukocytes? Sorry for the long post but I really appreciate your help!

 

[harrypotter]

-> Interstitial fluid is more likely to be facing basolateral surface since apical surface faces the lumen as in the case of kidney (nephron). If you read any physiology books describing the anatomy of kidney, you will see that interstitial fluid is on the basolateral side. Interstitila fluid, hence, could be extracellular fluid, and basolateral+apical sides are the surfaces separating lumen of a cell and extracellular matrix (sort of like E and B(?) of phospholipid bilayer).

Thank you soooo much!!

 

[MollyMalone]

Thanks, MollyMalone (and QofQuimica for letting her know). It's a lot clear in my mind now. However, I am just a bit confused about the presence of leukocytes in circulatory system and lymphatic system. Do both systems always have all leukocytes (lymphocytes, monocytes, megakaryotes, and other granular leukocytes such as neutrophils, basophils and eosinophils)? I realize all blood cells arise/differentiate from the bone marrow but where do granular leukocytes mature?
Also, if circulatory system contains leukocytes, what's the point of having a lymphatic system? I mean leukocyts in circulatory system will eliminate infecitons and other infective substances. Is it because circulatory sytem can't eliminate infections in interstitial fluid so lymphatic is present mainly for that purpose? Your explanation of the various purposes of lymphatic system is very concise and to the point, but I am just curious why we need lymphatic system if blood carries leukocytes (Does blood only carry T/B-cells+macrophages, or does it carry complete set of leukocytes?). Do lymphatic and circulatory system carry different leukocytes? Sorry for the long post but I really appreciate your help!

Well, keep in mind that the lymphatic system exists for other reasons, too. Even if it played no role in immunity, it would still be important.

But it is crucial for immunity, too.

All the different kinds of leukocytes are found in both the lymphatic and circulatory systems. However, although they are commonly called "white blood cells," all types spend most of their time outside the circulatory system, in the interstitial spaces and in the lymphatic system.

 

[pezzang]

The pH of the small intestine, accroding to EK bio, is ~6.5. On the other hand, pH of the small intestione, according to Kaplan's Bio lecutre, is 8.0. I know that the increase in pH from stomach to small intestine is due to the the influx of bicarbonate ions. So I have three questions:

1) Which pH of the small intestine is correct?

2) How does the bicarbonate ions flow into the small intestine and

3) what's the pathway for the bicarbonate ions? (i guess it starts by the product of aerobic respiration where CO2 is made and then flows into bloodstream(that's when CO2 -> HCO3) and into the capillaries of lung?!? But where/when/how bcarbonate ions flow into the small intestione?)

Thank you!

 

[QofQuimica]

The pH of the small intestine, accroding to EK bio, is ~6.5. On the other hand, pH of the small intestione, according to Kaplan's Bio lecutre, is 8.0. I know that the increase in pH from stomach to small intestine is due to the the influx of bicarbonate ions. So I have three questions:

1) Which pH of the small intestine is correct?

2) How does the bicarbonate ions flow into the small intestine and

3) what's the pathway for the bicarbonate ions? (i guess it starts by the product of aerobic respiration where CO2 is made and then flows into bloodstream(that's when CO2 -> HCO3) and into the capillaries of lung?!? But where/when/how bcarbonate ions flow into the small intestione?)

Thank you!

1) They both are; it depends on where in the SI you are talking about. In the duodenum, it's about 6.5. As you travel further through the SI, the pH rises to about 7.5.

2) They are produced by epithelial cells in the pancreatic ducts and released into the SI.

3) This is beyond the scope of what you need to know from the MCAT. But in a nutshell, the enzyme carbonic anhydrase catalyzes the combining of hydroxide ions with carbon dioxide to form bicarb. An antiporter (pump that exchanges ions in opposite directions) exports bicarb out of the cells in return for importing chloride.

 

[deleted106503]

Would questions on the MCAT about TATA, RNA Pol I,II, III be too much for the MCAT to ask? I have EK, which I don't think stresses this area that much and I've heard the MCAT has been going down this road more for questions. Let me know if I need to know it and I'll head on over to wikipedia.

 

[QofQuimica]

Would questions on the MCAT about TATA, RNA Pol I,II, III be too much for the MCAT to ask? I have EK, which I don't think stresses this area that much and I've heard the MCAT has been going down this road more for questions. Let me know if I need to know it and I'll head on over to wikipedia.

Wikipedia is not a verified source, so be careful about believing everything you read there. Although apparently the science entries are fairly accurate, but the political ones aren't.

I don't think it would hurt to be familiar with those topics, but I wouldn't stress out about memorizing all of the details of transcription, either. You're better off spending that time doing extra practice tests instead of memorizing science minutiae.

 

[deleted106503]

Wikipedia is not a verified source, so be careful about believing everything you read there. Although apparently the science entries are fairly accurate, but the political ones aren't.

I don't think it would hurt to be familiar with those topics, but I wouldn't stress out about memorizing all of the details of transcription, either. You're better off spending that time doing extra practice tests instead of memorizing science minutiae.

Thanks! Yes, wiki isn't the most reliable (at least for some automobiles I've read on). I guess I'll have to wip out the ole' bio book from the garage. I'm vaguely familiar with the subjects. Three weeks from the exam seems like way too much time so I guess this will just help burn it.

 

[pezzang]

If lymph nodes are the swellings along lymph vessels contaiing leukocytes, why does swelling of lymph nodes indicate that the person is sick? Shouldn't the swelling go down since there will be more leukocytes used and hence the vessels shrink? Or is it because more leukocytes are produced in response to the infection/virus? Thanks.

 

[Krazykritter]

Lymph nodes are classified as secondary lymphoid tissue. However, lymph nodes contain primarily lymphocytes (not leukocytes).

In the immune response at the lymph node level, afferent lymph flows through, providing antigens to the antigen presenting cells in the paracortex of the node. If antigen is recognized, an immune response is generated. This is the point at which swelling occurs...Replication of antibody producing B cells occurs cortical area of the lymph node causing characteristic swelling.

That answer may be slightly beyond the scope of the MCAT, but it is the answer to your question of the enlargement of lymph nodes.

 

[deleted106503]

Hi again, I went through the list of MCAT topics and found skimpy information in my review books or old textbooks for these. If someone could write up a quick summary on each of these topics, that'll be extremely helpful. Thanks!

Specifc coupling of free nucleic acids
Cancer as a failure of normal cellular controls
Oncogenes
Post-transcriptional control (GEC)
Genes: recombination, single and double crossovers
Prokaryotic Cell: Plasmids and extragenomic DNA
Hardy Weinberg Principle

Travelbug, QofQ, etc, I looked through the thread and some of these questions weren't answered. I'm not sure on some of them.

What is meant by specific coupling of free nucleic acids? Does this mean that G and C will hydrogen bond together if they're in their free form? A and T as well?

What is meant by Post-transcriptional control (GEC)? Is this intron splicing?

Genes: recombination, single and double crossovers. Could this be explained as well? I'm not sure if they mean for F+ and F-, tetrads, or maybe more examples.

Finallly, "Prokaryotic Cell: Plasmids and extragenomic DNA." Plasmids were discussed, but not extragenomic. Are these considered the same? Would the DNA in mitochondria be referred to as extragenomic or plasmid? I'm not sure if it's circular or not. I think in the symbiont (sp?) theory I read it said mitochondrian have circular DNA.

Any help would be appreciated.

 

[QofQuimica]

Travelbug, QofQ, etc, I looked through the thread and some of these questions weren't answered. I'm not sure on some of them.

What is meant by specific coupling of free nucleic acids? Does this mean that G and C will hydrogen bond together if they're in their free form? A and T as well?

What is meant by Post-transcriptional control (GEC)? Is this intron splicing?

Genes: recombination, single and double crossovers. Could this be explained as well? I'm not sure if they mean for F+ and F-, tetrads, or maybe more examples.

Finallly, "Prokaryotic Cell: Plasmids and extragenomic DNA." Plasmids were discussed, but not extragenomic. Are these considered the same? Would the DNA in mitochondria be referred to as extragenomic or plasmid? I'm not sure if it's circular or not. I think in the symbiont (sp?) theory I read it said mitochondrian have circular DNA.

Any help would be appreciated.

We're still working on writing up more explanations....most of the volunteers are med students, so they're pretty busy. But hopefully we'll have some more soon. I'm wanting to finish up the organic spectroscopy and purification methods at some point....

1) I'm not sure....maybe they meant polymerization of nucleic acids? I think that would make more sense in this context.

2) Right, that's an example of it. Basically the mRNA of eukaryotes is processed before it gets translated.

3) This definitely needs a whole post, and I can't do it right now.

4) Yes, plasmids are extragenomic, and so are mitochondrial DNAs. Yes, mitochondria have circular DNA.

 

[tik-tik-clock]

What is cell line viability and what are basal cellular activities?

Thanks! .

 

[Krazykritter]

Kind of vague question, but:

Cell line viability is the ability for a culture of cells to survive to pass on their genes to their daughter cells.

Basal cellular activities are the minimal processes a cell must carryout to survive. I'm not a cell biologist, but these generally include processes such as glycolysis (for energy) to produce the energy they need to replicate their genes & go through reproduction. However, if you are talking about the human body...the largest portion of basal cellular activities is protein turnover as well as other active metabolic processes.

 

[t2oo5]

Really simple question.
Blood that is pumped through the heart; is that purely red blood cells, or RBCs + Insterstital Fluid? For some reason, I had the notion that blood pumped through the heart is restricted to red blood cells & hemoglobin. But when I think of it, the blood that circulates through the heart does include interstitial fluid, correct?

 

[Krazykritter]

Blood pumped through the entire body is whole blood meaning it contains erythrocytes, platelets, leukocytes, plasma, etc. The only places I can recall off the top of my head where blood gets filtered or loses some of its constituents is; 1) In the capillaries when plasma oncotic & osmotic pressure favor the movement of fluid in & out of vessels. 2) In the glomeruli of the kidney.

I cannot, for any reason, think of a situation where blood would ever contain only RBC's & hemoglobin under normal physiologic conditions. Someone please correct me if I am wrong here.

 

[QofQuimica]

Blood pumped through the entire body is whole blood meaning it contains erythrocytes, platelets, leukocytes, plasma, etc. The only places I can recall off the top of my head where blood gets filtered or loses some of its constituents is; 1) In the capillaries when plasma oncotic & osmotic pressure favor the movement of fluid in & out of vessels. 2) In the glomeruli of the kidney.

I cannot, for any reason, think of a situation where blood would ever contain only RBC's & hemoglobin under normal physiologic conditions. Someone please correct me if I am wrong here.

No, I think you're right. The only other thing I'd add is that interstitial fluid is by definition NOT part of the blood. Maybe the person meant to say plasma?

 

[t2oo5]

No, I think you're right. The only other thing I'd add is that interstitial fluid is by definition NOT part of the blood. Maybe the person meant to say plasma?

What had me confused was this Wikipedia article on the lymphatic system:
"Lymph originates as blood plasma that leaks from the capillaries of the circulatory system, becoming interstitial fluid, filling the space between individual cells of tissue. Plasma is forced out of the capillaries by hydrostatic pressure, and as it mixes with the interstitial fluid, the volume of fluid accumulates slowly. Most of the fluid is returned to the capillaries by osmosis. The proportion of interstitial fluid that is returned to the circulatory system by osmosis is about 90% of the former plasma, with about 10% accumulating as overfill. The excess interstitial fluid is collected by the lymphatic system by diffusion into lymph capillaries, and is processed by lymph nodes prior to being returned to the circulatory system. Once within the lymphatic system the fluid is called lymph, and has almost the same composition as the original interstitial fluid."

It makes it seem as if all of the interstitial fluid is returned to the capillaries via mostly by osmotic pressure, then returned through the lymphatic system.

 

[Krazykritter]

t2oo5,

Let me try to clarify...

Plasma leaks through the fenestrated capillaries into the interstitium then becoming interstitial fluid. 90% of this fluid is returned to the capillaries to reunite w/ the plasma from which it came. 10% of it is then drained through the lymphatic system. The lymphatic system is a drainage system which drains in the subclavian vv.

If the lymphatic system did not drain the remainder of the fluid in the interstitium, you would develop massive amounts of edema.

 

[87138]

So does fermentation produce ATP or not? EK says 2ATP, but another source (I forget which . . . maybe Kaplan?) says no ATP. What's the right answer?

 

[Nutmeg]

So does fermentation produce ATP or not? EK says 2ATP, but another source (I forget which . . . maybe Kaplan?) says no ATP. What's the right answer?

The first step in fermentation is glycolysis, which produces the ATP. The next step--the step that is actually called fermentation and which produces the lactate or EtOH--regenerates the NAD+, but doesn't produce more ATP. So a cell subsisting on fermentation will get it's ATP from the gycolysis step of the fermentation pathway. Hence, it depends on whether you mean "fermentation" broadly or strictly.

http://sun.menloschool.org/~dspence/biology/chapter8/images/fermentation.jpg

 

[87138]

The first step in fermentation is glycolysis, which produces the ATP. The next step--the step that is actually called fermentation and which produces the lactate or EtOH--regenerates the NAD+, but doesn't produce more ATP. So a cell subsisting on fermentation will get it's ATP from the gycolysis step of the fermentation pathway. Hence, it depends on whether you mean "fermentation" broadly or strictly.

http://sun.menloschool.org/~dspence/biology/chapter8/images/fermentation.jpg

Thanks. I meant it "strictly" as in directly following glycolysis.

 

[pezzang]

I am having trouble with terminologies of Mitosis.

1) During prophase, centrioles move to opposite ends of the cell. Centrioles are made up of microtubules. So does it mean that it pulls spindle appratus? Is the function of the centrioles to produce cilia and flagella, which moves choromosomes?
Is the spindle appratus also microtubule? IF not, what is it exactly? Just protein?

2) Also, what kind of prtein is centromere that is located inthe middle of the chromosomes? Also, how is centromere attached to the spindle appratus? Am I right to think that the spindle apparatus and centromeres are both made up of microtubules? If not, what is it really?
Finally, what's the difference between kinetochore and centromere in terms of their functions and locations?

3) Is the spindle appratus the same as mitotic spindle, which,EK bio says,is a microtubule?

I have looked a few molecular biology books but they only have diagrams and pictures without detailed labelling of which one is called what. Please help me.

I really appreciate help.

 

[QofQuimica]

I am having trouble with terminologies of Mitosis.

1) During prophase, centrioles move to opposite ends of the cell. Centrioles are made up of microtubules. So does it mean that it pulls spindle appratus? Is the function of the centrioles to produce cilia and flagella, which moves choromosomes?
Is the spindle appratus also microtubule? IF not, what is it exactly? Just protein?

2) Also, what kind of prtein is centromere that is located inthe middle of the chromosomes? Also, how is centromere attached to the spindle appratus? Am I right to think that the spindle apparatus and centromeres are both made up of microtubules? If not, what is it really?
Finally, what's the difference between kinetochore and centromere in terms of their functions and locations?

3) Is the spindle appratus the same as mitotic spindle, which,EK bio says,is a microtubule?

I have looked a few molecular biology books but they only have diagrams and pictures without detailed labelling of which one is called what. Please help me.

I really appreciate help.

1) The centrioles are the anchors for the mitotic spindle. They have nothing to do with flagella and cilia besides being composed of microtubules. Flagella and cilia are involved with motion of the entire cell, not the chromosomes. What happens during cell division is that the spindle apparatus anchors on the centrioles at the cell poles, and the kinetochores of the chromosomes in the center of the cell. Then the shortening of the spindles (via disassembly of the microtubule subunits) causes the chromosomes to separate and move to opposite poles.

2) The centromere is not a protein; it's the center section of the chromosome (DNA). The kinetochore, which is where the spindle fibers attach, is located at the centromere. I'm sorry, but I don't know specifically how the spindle fibers attach to the kinetochore. That's definitely way more detail than what you need to know for the MCAT; they haven't even made us learn that in medical school!

3) Yes. Spindle fibers are composed of microtubules.

 

[hmcalley]

Prepping for Jan MCAT... and having trouble with Hardy-Weinberg.

If 100 green peas (CC) and 100 yellow peas (CC) are allowed to mate randomly, will the genotype frequencies in the next generation (F1) be the same? If not, why not?

Ans: No. The next generation will include CC, Cc, and cc genotypes. The population was not at Hardy-Weinberg equilibrium to start out.

I was thinking that CC x cc would only give Cc. Allele frequencies of the parent generation and F1 generation would not change. C=1/2 and c=1/2. Genotype frequencies did change because in the parent generation, there is ½ CC and ½ cc. In the F1 generation, there’s 100% Cc. I think my reasoning is wrong… help? Is the parent and F1 generations both in Hardy-Weinberg equilibrium?

I don't think I understand Hardy-Weinberg.

Thanks.

 

[QofQuimica]

Prepping for Jan MCAT... and having trouble with Hardy-Weinberg.

If 100 green peas (CC) and 100 yellow peas (CC) are allowed to mate randomly, will the genotype frequencies in the next generation (F1) be the same? If not, why not?

Ans: No. The next generation will include CC, Cc, and cc genotypes. The population was not at Hardy-Weinberg equilibrium to start out.

I was thinking that CC x cc would only give Cc. Allele frequencies of the parent generation and F1 generation would not change. C=1/2 and c=1/2. Genotype frequencies did change because in the parent generation, there is ½ CC and ½ cc. In the F1 generation, there’s 100% Cc. I think my reasoning is wrong… help? Is the parent and F1 generations both in Hardy-Weinberg equilibrium?

I don't think I understand Hardy-Weinberg.

Thanks.

I think you are interpreting the question wrong. What I mean is, it seems like they are trying to ask you if the genotypes of all of the F1 generation are the same as the genotypes of the parents. In this case, they definitely are not. You have three possible scenarios: you could have CC x CC, CC x cc, or cc x cc. Since the plants mate randomly, you can wind up with all three types of offspring in the F1 generation (CC, Cc, and cc). That is, you can have green x green and yellow x yellow crosses too, not just green x yellow, which is the one that you were thinking about. Since Mendel isn't here forcing the greens to only mate with yellows and vice versa, you'll get some greens mating with greens and yellows mating with yellows too. Does that help?

This is really not a Hardy-Weinberg question at all. Those questions are the ones where they have to give you either the frequency of one of the phenotypes (ex. you have a 3% occurrence of cc recessive homozygotes in the population; how many Cc heterozygotes are there?) or the frequency of an allele (ex. 3/10 peas are green versus 7/10 are yellow. How many are heterozygotes?) and then ask you to calculate some other parameter. I think they are just trying to point out to you that Hardy-Weinberg conditions aren't met, so you CAN'T use the H-W equations in this case even if you wanted to do that. There are several conditions that must be met for you to be able to use the equations, including having a large population, no mutations, no individuals entering or leaving the population, random mating, and a fifth one that I can't think of at the moment.

 

[hmcalley]

Thanks QofQuimica. I don't think I would have ever figured it out! Thanks!

 

[QofQuimica]

bump

 

[tik-tik-clock]

What makes O2 an hydrophobic molecule

 

[Captain Fantastic]

What makes O2 an hydrophobic molecule

It's not charged and is non-polar.

 

[QofQuimica]

What makes O2 an hydrophobic molecule

http://forums.studentdoctor.net/showpost.php?p=2756252&postcount=4

Read the section about nonpolar covalent bonds.

 

[QofQuimica]

bumpity

 

[NontradICUdoc]

Genes: recombination, single and double crossovers. Could this be explained as well? I'm not sure if they mean for F+ and F-, tetrads, or maybe more examples.

Any help would be appreciated.

During metaphase of meiosis , you have the alleles lined up in the metaphase plate. During this time, there is a chance for the alleles to exchange genes. This is known as recombination, because genes between the alleles can be switched. For example, let us say that your father has the genes for blue eyes and blonde hair while your mother has the genes for brown eyes and brown hair. During metaphase (I believe it to be metaphase 1) the alleles line up and the genes for eye color cross over. A single recombination event, because only 1 gene was exchanged. Now the alleles code for blue eyes and brown hair on the first allele and brown eyes and blonde hair on the second allele.

Now let's add a third gene to the allele, curly hair or straight hair. So now, your father has the genes for blue eyes, blonde hair, and straight hair while your mother has the genes for brown eyes, brown hair, and curly hair.

During metaphase 1, genes are recombined. If there was a single cross over event, then you would have blue eyes, brown hair, curly hair on the first allele. And brown eyes, blonde hair, straight hair on the second allele. If there was a second cross over event, then you would have a double cross over and the alleles would be blue eyes, brown hair, straight hair for one and brown eyes, blond hair, curly hair for the second.

F+ and F- are for the sex pillus in bacteria. An F+ bacteria and extend the sex pillus to give a copy of their plasmid to another bacteria generally an F- and giving the recipient and F+ gene making it an F+ bacteria. This has nothing to do with recombination.

I hope this helps.

 

[QofQuimica]

During metaphase of meiosis , you have the alleles lined up in the metaphase plate. During this time, there is a chance for the alleles to exchange genes. This is known as recombination, because genes between the alleles can be switched. For example, let us say that your father has the genes for blue eyes and blonde hair while your mother has the genes for brown eyes and brown hair. During metaphase (I believe it to be metaphase 1) the alleles line up and the genes for eye color cross over. A single recombination event, because only 1 gene was exchanged. Now the alleles code for blue eyes and brown hair on the first allele and brown eyes and blonde hair on the second allele.

Now let's add a third gene to the allele, curly hair or straight hair. So now, your father has the genes for blue eyes, blonde hair, and straight hair while your mother has the genes for brown eyes, brown hair, and curly hair.

During metaphase 1, genes are recombined. If there was a single cross over event, then you would have blue eyes, brown hair, curly hair on the first allele. And brown eyes, blonde hair, straight hair on the second allele. If there was a second cross over event, then you would have a double cross over and the alleles would be blue eyes, brown hair, straight hair for one and brown eyes, blond hair, curly hair for the second.

F+ and F- are for the sex pillus in bacteria. An F+ bacteria and extend the sex pillus to give a copy of their plasmid to another bacteria generally an F- and giving the recipient and F+ gene making it an F+ bacteria. This has nothing to do with recombination.

I hope this helps.

Crossovers actually start occurring in prophase I when the homologs pair up. Other than that, great post.

P.S. I got your PM and I will respond later.

 

[Whwsf]

Hi i have a question on osmolarity. in the Kap Biology Discrets 2 test, the question What happens when there is insufficient ADH secretion

a) Increased Urine Osmolarity
b) Increased urine volume


i know that the answer is B becasue when no ADH is secreted, water volume goes up but why is decreased urine osmolarity an effect of insufficient ADH.

am i totally off in my reasoning or does osmolarity not mean H2O Concentration?

 

[rcd]

Hi i have a question on osmolarity. in the Kap Biology Discrets 2 test, the question What happens when there is insufficient ADH secretion

a) Increased Urine Osmolarity
b) Increased urine volume


i know that the answer is B becasue when no ADH is secreted, water volume goes up but why is decreased urine osmolarity an effect of insufficient ADH.

am i totally off in my reasoning or does osmolarity not mean H2O Concentration?

osmolarity means concentration of solutes in H2O, not H2O concentration.

 

[lovechild404]

1) In designing antibiotics to treat infections caused by faculative anaerobes in humans, the target which would be most attractive are inhibitors of bacterial:
a. mRNA splicing
b. electron transport
c. poly-A addition for mRNAs
d. transcription
e. none of the above

2) When measuring reaction velocity as a function of substrate concentration, a researcher usually keeps the concentration of enzyme at a constant level. WHat would happen if the enzyme concentration were NOT kept constant?
a. Vmax would stay constant, but V would change
b. Vmax would stay constant, but Km would change
c. Vmax would change, but Km would remain constant
d. Both Vmax and Km would change
e. none of the above would necessarily occur

3) Which of the following sensory receptors are Not mecanoreceptors?
a. aortic baroreceptor
b. hearing receptors in the Organ of Corti
c. rods and cones
d. pacinian corpuscles
e. golgi tendon organs

4) A competitive inhibitor causes:
a. Vmax to decrease and Km to stay unchanged
b. Vmax to stay unchanged and Km to decrease
c. Vmax to stay unchanged and Km to increase
d. Vmax to increase and Km to remain unchanged
e. neither Vmax or Km will be affected.

5) Is prokaryotic mRNA monocistronic?
a. true
b. false

6) Including the ATP used for amino acid activation/tRNA loading, approximately how many ATP equivalents are required to synthesize a 200 amino acid protein?
a. 200
b. 400
c. 600
d. 800
e. 1000

 

[juventusman31]

[deleted] (forgot to read the introductory sticky note)

 

[lisichka]

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[lisichka]

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[lisichka]

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[midn]

Deleted

 

[Renae24]

Maybe this has been asked before... if so, sorry I couldn't find it. Anyways, under genetics and mendelian concepts it says "leakage". Anyone know what this is? I have looked through genetics book and can't find anything.

 

[spicedmanna]

Maybe this has been asked before... if so, sorry I couldn't find it. Anyways, under genetics and mendelian concepts it says "leakage". Anyone know what this is? I have looked through genetics book and can't find anything.

Already answered. Check:

http://forums.studentdoctor.net/showpost.php?p=3539789

 

[Renae24]

thank you!!