Biochemistry, cell biology, and genetics question thread

[Nutmeg]

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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.

 

[QofQuimica]

1. why is dna phosphate group acidic?
Is it the the oxygens pulling all the electrons away?

2. Can someone explain to me how acidic and basic side chains of amino acids vs positive and negative charges and what kind of molecules they react with.

See if this helps answer your question: http://forums.studentdoctor.net/showpost.php?p=3359304&postcount=258

I don't understand exactly what you're asking in your second question. Are you asking what the charge is on acidic and basic side chains? Acidic groups will be deprotonated, and therefore negatively charged. Basic groups will be protonated, and therefore positively charged.

 

[kevin86]

are u sure it's the phosphoric acid thats acidic? isnt there only one H+ throughout the chain. Wouldn't the electro negative oxygens make the every phosphate in the esster groups all somewhat positive.

As for the second question, I actually wanted to know more like the isoletric point and so on, and how that relates to charges.

 

[QofQuimica]

are u sure it's the phosphoric acid thats acidic? isnt there only one H+ throughout the chain. Wouldn't the electro negative oxygens make the every phosphate in the esster groups all somewhat positive.

As for the second question, I actually wanted to know more like the isoletric point and so on, and how that relates to charges.

Are you asking about the individual phosphorus atoms? 😕 Phosphoric acid is the whole *molecule*, not just one atom. The phosphate group *as a whole* is acidic. You are seeing the O's with negative charges because they have been deprotonated. In other words, the pKa of phosphoric acid is lower than 7, so at neutral pH, they will get deprotonated. Remember that the def. of an acid (Bronsted Lowry) is that the compound will donate an H. You are seeing the negatively charged phosphate conjugate bases left behind after the proton transfer has occurred.

An amino acid reaches its isoelectric point when it's a zwitterion. In other words, the amino group will be protonated and the acid group will be deprotonated so that the molecule is not charged overall. This will happen at a different pH for each amino acid, which is how isoelectric focusing (where you subject the aa's to a charge and run them through a gel) works. A few aa's have charged side chains, and they will reach their isoelectric point when they have one positive basic group, one negative acidic group, and the third group (acidic or basic) is neutral.

 

[kevin86]

Ok I understand now. So just to clarify the the phosphate chain originally all contained protons, that dissociated at physiological pH correct? But then are the phosphourus atoms somewhat positive as well or not?

This also helps me a lot about the amino acid questions. So are acidic amino acids negative at physiological pH and bind to positive molecules because the side chain carboxyl group loses deprotonates? and the opposite with basic groups?

The side chains in both single and polypeptides are the only thing that binds to other molecules right as opposed to the amide NH3 and COOH groups?

 

[QofQuimica]

Ok I understand now. So just to clarify the the phosphate chain originally all contained protons, that dissociated at physiological pH correct?

yes

But then are the phosphourus atoms somewhat positive as well or not?

Yes, the phosphorus atoms will have a partial positive charge on them due to their being bonded to the more electronegative oxygen atoms. There is an inductive withdrawal of electron density from P due to the electronegativity difference.

This also helps me a lot about the amino acid questions. So are acidic amino acids negative at physiological pH and bind to positive molecules because the side chain carboxyl group loses deprotonates? and the opposite with basic groups?

yes

The side chains in both single and polypeptides are the only thing that binds to other molecules right as opposed to the amide NH3 and COOH groups?

That is often true because the amide backbones tend to participate in secondary structure formation. In other words, the amides will hydrogen bond to one another to form alpha helices and beta sheets. There are probably some examples where the backbone also can interact with other molecules though, so I'd hesitate to say "only."

 

[kevin86]

so to be a bother, but back to the positive phosphorus question, would it be acidic? Since the it does get positive, does histidine and other basic amino acid bind to it during regular cell cycles. Also is the basicity of the bases neutralized by the overall phosphoric acidic nature?

 

[Cooolguy]

hey i need help on something. I am confused about the whole equation:
H+ + HCO3- --> H2CO3 --> H20 + CO2

what happens when there is excess/or not enough H+ or excess CO2 in terms of respiration (hyperventilate, hypoventilate) and in terms of the hemoglobin saturation curve?? i cant seem to get this, please help.

 

[Mr. Three-Wiggle]

It is my understanding that the Bohr Shift applies to the hemoglobin binding curve and its reaction to varying conditions ie. it shifts right under hot acidic environments and left in cold basic environments.

As you can see from your equation and Le Chatlier's Principle during hyperventilation you breathe off all of your CO2. This causes a shift to the right (in the equation) to make up for the lost CO2 making your blood more basic. In hypoventilation the opposite is happening. You keep the CO2 in your lungs and drive the equilibrium to the left creating more acid (this is why you breathe into a paper bag - to breathe in CO2 and make your blood more acidic to get back to physiological pH.

 

[Sol Rosenberg]

hey i need help on something. I am confused about the whole equation:
H+ + HCO3- --> H2CO3 --> H20 + CO2

what happens when there is excess/or not enough H+ or excess CO2 in terms of respiration (hyperventilate, hypoventilate) and in terms of the hemoglobin saturation curve?? i cant seem to get this, please help.

Think about the answers to your questions in terms of LeChatlier's principle. In the equation(s) that you wrote above, an excess of H+ will tend to push the reaction to the right. This is one way in which the body deals with acidosis (acidic blood) by forming more H2CO3 from H+ and HCO3-, which subsequently decomposes in the lungs, releasing CO2. Excess CO2 (like in the tissues) would tend to push the reaction to the LEFT. The CO2 will dissolve in the blood as H2CO3 (which may dissociate to H+ and HCO3-).

The Bohr shift is the tendency for Hemoglobin to have a reduced affinity for oxygen at low pH (one cause of low pH could be high CO2, but there are others.) The lower affinity for O2 would cause the hemoglobin saturation curve to shift to the RIGHT.

Does that make sense?

Jota

 

[MedicineNutt]

What is the difference between phase of mitosis and meiosis??? stupid question, but a refresher for me... i know meisosis skips something though

 

[QofQuimica]

What is the difference between phase of mitosis and meiosis??? stupid question, but a refresher for me... i know meisosis skips something though

Maybe you're thinking that meiosis II does not have a round of DNA replication preceding it like mitosis and meiosis I both do? The phases are the same: prophase, metaphase, anaphase, and telophase. One key difference is that in meiosis I, the chromosomes line up double-file in homologous pairs along the metaphase plate instead of single-file like they do in mitosis and meiosis II.

 

[MedicineNutt]

Maybe you're thinking that meiosis II does not have a round of DNA replication preceding it like mitosis and meiosis I both do? The phases are the same: prophase, metaphase, anaphase, and telophase. One key difference is that in meiosis I, the chromosomes line up double-file in homologous pairs along the metaphase plate instead of single-file like they do in mitosis and meiosis II.

ohhhhhhhhhh now i remember...thanks thanks...yes, metaphase is different in both stages--the answer i was lookin for!!!

 

[LT2]

Maybe you're thinking that meiosis II does not have a round of DNA replication preceding it like mitosis and meiosis I both do? The phases are the same: prophase, metaphase, anaphase, and telophase. One key difference is that in meiosis I, the chromosomes line up double-file in homologous pairs along the metaphase plate instead of single-file like they do in mitosis and meiosis II.

don't forget there is also crossing over in meiosis between homologous pairs when the chromosomes line up double-file...

 

[LT2]

hey i need help on something. I am confused about the whole equation:
H+ + HCO3- --> H2CO3 --> H20 + CO2

what happens when there is excess/or not enough H+ or excess CO2 in terms of respiration (hyperventilate, hypoventilate) and in terms of the hemoglobin saturation curve?? i cant seem to get this, please help.

to build on what others have said about the bohr shift... you can also think of H+ in terms of an allosteric regulator of hemoglobin. when there is a lot of H+ around, it binds hemoglobin and decreases its affinity for oxygen. if the affinity for oxygen is decreased, the curve will shift to the right. this means it will take a higher partial pressure of oxygen (more oxygen) in order for Hb to bind it. physiologically, it makes sense. if your muscles are working really hard, they need oxygen, so you don't want the Hb to be bound to oxygen in the muscles, you want it to be released and utilized by the muscles. hope that makes some sense.

 

[Lests55]

I have a question about animal viruses. I know they contain a lipid/protein envelope (similar to a plasma membrane), but does this mean that they lack a capsid that bacteriophages have?

 

[Krazykritter]

I have a question about animal viruses. I know they contain a lipid/protein envelope (similar to a plasma membrane), but does this mean that they lack a capsid that bacteriophages have?

Viruses accomplish the "capsid" that bacteriophages have by using an envelope. Some families of viruses, have capsids (Bunyavirus, Paramyxovirus) and others do not (Adeno, Picorona). I believe that the capsid of a bacteriophage and the envelope of a virus are analogous in that they both attempt to provide protection from the immune system and also contain binding proteins.

 

[QofQuimica]

I have a question about animal viruses. I know they contain a lipid/protein envelope (similar to a plasma membrane), but does this mean that they lack a capsid that bacteriophages have?

No, as far as I know, all viruses contain genetic material in the center, surrounded by a protein capsid. Some also have an envelope as well, surrounding the capsid. If any of the biologists know of an exception, please feel free to educate us all. 🙂

 

[travelbug73]

No, as far as I know, all viruses contain genetic material in the center, surrounded by a protein capsid. Some also have an envelope as well, surrounding the capsid. If any of the biologists know of an exception, please feel free to educate us all. 🙂

As always, Q is correct, unless the OP is thinking of viriods (associated with plant disease). Of course, there are no known human pathogenic viriods. But there is one that resembles a viriod and that is hepatitis delta agent. However, unlike true viriods it is packaged.

 

[hmm...]

What is leakage? it is a heading in the aamc topic headings, but I could not find this anywhere. 😕

thx

 

[QofQuimica]

What is leakage? it is a heading in the aamc topic headings, but I could not find this anywhere. 😕

thx

Please don't start new threads; just post in the appropriate existing question thread.

Genetic leakage is when genes flow from one species to another. This is a concern for things like GM foods or antibiotic resistance, where genes are able to cross species.

 

[shnjb]

WTF is "selected against" and "selected for" nonsense?

"If none of the Xi-bearing genotypes is selected against, then the frequency of Xi is expected to increase to 100%, unless other genes act to suppress expression of e and f."

 

[QofQuimica]

WTF is "selected against" and "selected for" nonsense?

"If none of the Xi-bearing genotypes is selected against, then the frequency of Xi is expected to increase to 100%, unless other genes act to suppress expression of e and f."

A trait that is "selected against" is one that is unfavorable for reproductive success, while one that is "selected for" allows for greater reproductive success. Probably the most famous example of this is with pepper moths. These moths can be either white or black. Originally, the white moths were most successful, because they could blend in with the bark of trees. In contrast, the black moths were readily eaten because the bird predators could easily see them. So white color was selected for, and black color was selected against. After the industrial revolution, the tree trunks became sooty. Now black moths could hide, while white moths stood out, and their roles reversed; black color became selected for, and white color selected against. Apparently nowadays the white color is again selected for due to anti-pollution laws.

 

[DougFlutie]

I have some questions about intersitial fluid.

I suppose my first question is: What is interstitial fluid? It was glossed over in EK as "the fluid between cells", but AAMC 9R had about 6 or 7 questions in which I wasn't sure what interstitial fluid was doing, how increasing albumin concentration affected interstitial fluid, how it plays in to the capillaries and tissue (relative pressures), and other such annoyances. What do we have to know about it? I really appreciate any help.

 

[QofQuimica]

I have some questions about intersitial fluid.

I suppose my first question is: What is interstitial fluid? It was glossed over in EK as "the fluid between cells", but AAMC 9R had about 6 or 7 questions in which I wasn't sure what interstitial fluid was doing, how increasing albumin concentration affected interstitial fluid, how it plays in to the capillaries and tissue (relative pressures), and other such annoyances. What do we have to know about it? I really appreciate any help.

Interstitial fluid is outside of cells, yes, but more importantly, it's outside the blood. It's the liquid in your tissues. Too much interstitial fluid will cause edema (swelling).

You don't need to know very much about interstitial fluid. A lot of questions asking you about how things like the albumin concentration affect the interstitial fluid are really testing you on your understanding of membrane transport (osmosis, diffusion). For example, if the blood albumin level goes down, the blood will not be hypertonic enough to reabsorb enough water from the tissues, and edema will result. If you need to know about the interstitial fluid in more detail, the passage should give you that info.

 

[DougFlutie]

Interstitial fluid is outside of cells, yes, but more importantly, it's outside the blood. It's the liquid in your tissues. Too much interstitial fluid will cause edema (swelling).

You don't need to know very much about interstitial fluid. A lot of questions asking you about how things like the albumin concentration affect the interstitial fluid are really testing you on your understanding of membrane transport (osmosis, diffusion). For example, if the blood albumin level goes down, the blood will not be hypertonic enough to reabsorb enough water from the tissues, and edema will result. If you need to know about the interstitial fluid in more detail, the passage should give you that info.

Thank you so much! 👍

 

[QofQuimica]

bump

 

[QofQuimica]

bump

 

[pezzang]

Hi, this might be a basic question, but what does plasma consist of and what's its function? My idea of plasma was a cell present in blood containing blood cells and proteins. What is the exact function of plasma and is it present in all blood (meaning in all blood vessels)? Thanks!!!!

 

[gridiron]

Hi, this might be a basic question, but what does plasma consist of and what's its function? My idea of plasma was a cell present in blood containing blood cells and proteins. What is the exact function of plasma and is it present in all blood (meaning in all blood vessels)? Thanks!!!!

Hey. Plasma is the liquid portion of blood and is where red blood cells are suspended. The constituents of plasma include: fibrinogen (a clotting factor synthesized by the liver), water, blood proteins like albumin (which maintains oncotic pressure in the blood) and globulins, and inorganic electrolytes. Plasma serves as the medium of transport of a variety of materials like glucose, hormones and lipids. Good luck!

 

[pezzang]

Hey. Plasma is the liquid portion of blood and is where red blood cells are suspended. The constituents of plasma include: fibrinogen (a clotting factor synthesized by the liver), water, blood proteins like albumin (which maintains oncotic pressure in the blood) and globulins, and inorganic electrolytes. Plasma serves as the medium of transport of a variety of materials like glucose, hormones and lipids. Good luck!

Hey BioMedEngineer. Thanks again. So plasma is the complete liquid portion of blood.. Is it true that only smooth muscles surround blood vessels? Also, is blood vessel phospholipid bilayer? Thanks!

 

[gridiron]

Hey BioMedEngineer. Thanks again. So plasma is the complete liquid portion of blood.. Is it true that only smooth muscles surround blood vessels? Also, is blood vessel phospholipid bilayer? Thanks!

Hey. No, it is not true that smooth muscle only surrounds blood vessels. Think about the characteristics of smooth muscle--it is not striated like skeletal muscle and surrounds hollow organs. Therefore, this type of muscle can be found where contraction is necessary---like the walls of the esophagus, the stomach, or the gastrointestinal track. Furthermore, this type of muscle can also be found in the bladder and the kidney. I just correlate smooth muscle to involuntary contraction--usually that fits most of the cases but not all.
Regarding your question on blood vessels---they are composed of different types of tissues like the endothelium and connective tissue--all are composed of cells which according to the fluid-mosaic model of the cell structure are composed of the a phospolipid bilayer. Remember, cells make up tissues and tissues make up organs...etc. I hope this helps and good luck!

 

[pezzang]

Hey. No, it is not true that smooth muscle only surrounds blood vessels. Think about the characteristics of smooth muscle--it is not striated like skeletal muscle and surrounds hollow organs. Therefore, this type of muscle can be found where contraction is necessary---like the walls of the esophagus, the stomach, or the gastrointestinal track. Furthermore, this type of muscle can also be found in the bladder and the kidney. I just correlate smooth muscle to involuntary contraction--usually that fits most of the cases but not all.
Regarding your question on blood vessels---they are composed of different types of tissues like the endothelium and connective tissue--all are composed of cells which according to the fluid-mosaic model of the cell structure are composed of the a phospolipid bilayer. Remember, cells make up tissues and tissues make up organs...etc. I hope this helps and good luck!

Wow!! Thanks again...haha..well, can i ask one more question? So what is the significance of "striatedness" on muscle like skeletal and cardiac but not smooth muscles?

 

[QofQuimica]

Wow!! Thanks again...haha..well, can i ask one more question? So what is the significance of "striatedness" on muscle like skeletal and cardiac but not smooth muscles?

The striations you see on skeletal and cardiac muscles are the sarcomeres. Smooth muscle doesn't have sarcomeres, so it isn't striated.

 

[pezzang]

The striations you see on skeletal and cardiac muscles are the sarcomeres. Smooth muscle doesn't have sarcomeres, so it isn't striated.

So as far as the function is concerned, does the fact that smooth muscle does not have sarcomeres while skeletal and cardiac muscles are striated create any differences in function?

 

[gridiron]

So as far as the function is concerned, does the fact that smooth muscle does not have sarcomeres while skeletal and cardiac muscles are striated create any differences in function?

Technically, no. Smooth, skeletal and cardiac muscle all contract but the arrangment of the muscle fibers are different. In smooth muscle, actin and myosin are arranged in bundles and in striated muscle they are arranged in sarcomeres. Both types use the hydrolysis of ATP to contract. However, smooth muscle uses the enzyme MLCK in muscle contraction. Hope this helps and good luck!

 

[ilovefood]

how does foreign DNA integrate itself into a genome?

does it just insert itself inside the host DNA, or does it do this by homologous recombination?

does recombination just happen on its own???

 

[QofQuimica]

how does foreign DNA integrate itself into a genome?

does it just insert itself inside the host DNA, or does it do this by homologous recombination?

does recombination just happen on its own???

This is not my area of expertise, but there are at least a few ways that it can happen. One possibility is that you can have a segment on the foreign DNA that is homologous to the host (ex. some sequence that is highly conserved), and basically a cross-over occurs. Another possibility is for a transposon to insert itself into the host DNA; the DNA does not have to have a homologous sequence in order for this to happen. Transposons can just insert randomly. There is also a nonhomologous end joining pathway in cells that normally functions to repair breaks in double stranded DNA. Since the breaks are ligated without any template, it would be possible for the enzymes involved to insert a foreign piece of DNA this way.

FYI, this question is more specific than what you need to know for the MCAT. 🙂

 

[laneyj34]

In electrophoresis, do all of the proteins, no matter their charge, move towards the anode? I had a question in one of the Kaplan books, I do not have it in front of me, but I believe that it said that proteins with a more negative overall charge would move towards the anode. Shouldn't opposite charges attract (in this case the negatively charged protein move towards the cathode)? Why do the negatively charged proteins move towards the anode (-)? Am I forgeting something from my bio class?

 

[xx216xx]

In electrophoresis, do all of the proteins, no matter their charge, move towards the anode? I had a question in one of the Kaplan books, I do not have it in front of me, but I believe that it said that proteins with a more negative overall charge would move towards the anode. Shouldn't opposite charges attract (in this case the negatively charged protein move towards the cathode)? Why do the negatively charged proteins move towards the anode (-)? Am I forgeting something from my bio class?

The anode is the positive electrode of an electrolytic cell

EDIT: Sorry, didn't realise I'm not suppose to answer questions.

 

[pezzang]

Is this a valid statement?

On pg 76 of EK Bio:

1. In order to reach the cytoplasm, a substance must cross a membran via passive or facillitated diffusion, or active transport, but it can reach the ER lumen via endocytosis without ever transporting across a membrane.

I realize what it says is true, but I think this statement implies that endocytosis cannot occur to move a substance (ie macromolecules) across phospholiquid bilayer between ECM and cytoplasm. I thought endocytosis can occur across the membrane that bound a cell (cytoplasm) as well as while crossing lumen of membrane-bound organelles. What do you think?

 

[QofQuimica]

Is this a valid statement?

On pg 76 of EK Bio:

1. In order to reach the cytoplasm, a substance must cross a membran via passive or facillitated diffusion, or active transport, but it can reach the ER lumen via endocytosis without ever transporting across a membrane.

I realize what it says is true, but I think this statement implies that endocytosis cannot occur to move a substance (ie macromolecules) across phospholiquid bilayer between ECM and cytoplasm. I thought endocytosis can occur across the membrane that bound a cell (cytoplasm) as well as while crossing lumen of membrane-bound organelles. What do you think?

No, I think you're misinterpreting their meaning. I think what they are trying to say is that in endocytosis, the injested molecules never are exposed to the cytoplasm. In other words, when you have molecules diffusing in (or actively transported in), they go from being on the outside of the cell to being in the cytosol. They have to cross a membrane to do that. But when you have endocytosed material, a vesicle is formed that invaginates inward from outside the cell, and the fluid inside that vesicle is continuous with the extracellular environment, not the cytosol. The vesicle travels across the cell and is exocytosed on the other side without ever having to cross a membrane and be exposed to cytosol. Does that make sense?

 

[pezzang]

No, I think you're misinterpreting their meaning. I think what they are trying to say is that in endocytosis, the injested molecules never are exposed to the cytoplasm. In other words, when you have molecules diffusing in (or actively transported in), they go from being on the outside of the cell to being in the cytosol. They have to cross a membrane to do that. But when you have endocytosed material, a vesicle is formed that invaginates inward from outside the cell, and the fluid inside that vesicle is continuous with the extracellular environment, not the cytosol. The vesicle travels across the cell and is exocytosed on the other side without ever having to cross a membrane and be exposed to cytosol. Does that make sense?

ABSOLUTELY FANTASTIC! 👍

 

[pezzang]

What's the effect of blood vessel dilation and increased permeability of capillaries during inflammation? Wouldn't blood vessel dilation cause less resistance to the blood flow and thus create higher hydrostatic force, allowing more loss of blood? As for the capillaries, increased permeability of capillaries decreases the loss of blood. So, in the case of inflammation, there is less blood lost. It seems that those two effects above are contradictory. Can somebody explain what's wrong? Thank you!

 

[deleted106503]

What exactly is a barr body and how does it affect the genotype of the offspring (if it dose at all)? EK confused me on this part. From what I read, I think one of the chromosomes of the mother compacts to a really small bundle called the barr body, I think. Then the other is the one that joines with one of the fathers (either X or Y) to become the ovum/zygote/child. I'm assuming the barr body is a random process, yes?

What was that other theory that didn't follow Mendel's dominant/recessive process? I think it was something along the lines of if a female recessive mates with a male dominant, the recessive trait will show because the female has it. Another could be that the male is recessive, but the traits show because it was a male. I think this was also done with flowers, but do we have to know this? I think it depended on sex more than dominant/recessive genes.

 

[pezzang]

What exactly is a barr body and how does it affect the genotype of the offspring (if it dose at all)? EK confused me on this part. From what I read, I think one of the chromosomes of the mother compacts to a really small bundle called the barr body, I think. Then the other is the one that joines with one of the fathers (either X or Y) to become the ovum/zygote/child. I'm assuming the barr body is a random process, yes?

What was that other theory that didn't follow Mendel's dominant/recessive process? I think it was something along the lines of if a female recessive mates with a male dominant, the recessive trait will show because the female has it. Another could be that the male is recessive, but the traits show because it was a male. I think this was also done with flowers, but do we have to know this? I think it depended on sex more than dominant/recessive genes.

Barr body is only produced from females and is a random process. Because female has XX in her sex chromosome, one of the two X's cannot be incorporated in making offspring (the other X/Y comes from the father; in the case the offspring receives Y, the offspring is a male; otherwise, female). You are right about one barr body, which becomes coiled up and is removed, and the other, which gets used in making a zygote.

The second question is about sex-linked genes. In sex-linked genes, only X can have recessive/dominant traits. Hence, male (XY) can only have either recessive or dominant trait and cannot be a carrier due to his Y. As for females, they can be carriers because they have XX so they can have one dominant and one recessive in a ressesive disease/trait. Because males only have one X, they do not receive any dominant/recessive trait from their fathers. However, their only expressable X gene comes from the mother, the son will get one X, which can be recessive or dominant. As for the daughter, she receives one X from father and the other X from mother so they are affected by both her father and her mother. I hope it helps!

 

[gridiron]

.

 

[gridiron]

What's the effect of blood vessel dilation and increased permeability of capillaries during inflammation? Wouldn't blood vessel dilation cause less resistance to the blood flow and thus create higher hydrostatic force, allowing more loss of blood? As for the capillaries, increased permeability of capillaries decreases the loss of blood. So, in the case of inflammation, there is less blood lost. It seems that those two effects above are contradictory. Can somebody explain what's wrong? Thank you!

Actually, blood vessel dilation creates less hydrostatic force and minimizes blood pressure. An example of a vasodilator agent is nitric oxide. Remember, blood pressure is the pressure exerted by blood on the walls of vessels--vasoconstriction would increase this pressure. In the case of inflammation, capillary permeability increases for the passage of phages and other substances to the site of injury. Since the hydrostatic pressure created by the heart to pump blood throughout the body decreases with increased cross sectional area from the aorta, pressure is relatively small in the capillaries to promote the diffusion of substances like nutrients, oxygen and carbon dioxide. When the permeability of the capillary is increased, more substances are allowed to move freely throught, increasing loss. Remember, dilate means to increase---dilate the eyes, dilate the blood vessels. FYI: There are several vasodilator drugs in the market like Tadalafil. Recognize this generic name---the brand name is Cialis a drug used to treat impotence. Another drug is sildenafil whose brand is........Viagra. Interestingly enough, these drugs enhance the effect of nitric oxide in blood vessels.

 

[pezzang]

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!!!

 

[harrypotter]

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!

 

[Dr Durden]

in vivo = in a living organism
in vitro = in glass or in an artificial environment outside of an organism

Both usually refer to experimental set-ups.