Biology/General Chem/Organic Chem questions

[oohpsjin]

Hi

 

I have quite a few questions about biology and general chemistry from studying the Kaplan Premier Program 2008/09 textbook.

 

1. Our body has four types of tissue: epithelial, connective, nervous, and muscle. But what kind of a tissue is the liver? Is it a blend of more than one tissue?

 

2. I only learned when genetic material and the cytosol divide during cell division (mitosis). But when do the cell organelles (mitochondria, Golgi etc.) divide and how?

 

3. Question regarding multiple births. Is it possible to have dizygotic (fraternal) fertilization in the beginning, followed by a zygotic split in just one of the two zygotes, so that there are triplets (two offspring that are identical, and one that is fraternal to the other two)?

 

4. I can't seem to understand the difference in functions between memory T cells and memory B cells in the human immune system. Are they simply different by their origin?

 

5. Cortisol is released in response to stress in the human body. But one of its function is to reduce the immune system's potency. How would this be beneficial to the individual? Shouldn't the effect be opposite, and the body strengthen immune system to prevent any infections due to stress?

 

6. What exactly is the difference between epinephrine and norepinephrine. And please, no copy and paste information from wikipedia. Tried it all.

 

7. How is the definition of "homozygous" any different from "true-bred"? If there are any differences, how are they different? (examples plz?)

 

8. Hardy-Weinberg Equilibrium Equation: p^2 + 2pq +q^2 = 1.

 

For p = 0.8 and q=0.2, the equation works when crossing two heterozygotes in a nonevolving population (no microevolution): The final gene frequencies add up to p = 0.8 and q = 0.2. But I tried this for crossing a homozygote dominant (p) with a heterozygote...and the frequencies CHANGED to p=0.9, and q=0.1. Shouldn't the gene frequencies remain constant for any random cross in a nonevolving population according to the HW equation?

 

General Chemistry questions

9. The ionization energy is defined as the energy required to completely remove an electron from a gaseous atom or ion. Electron affinity is defined as the energy change that occurs when an electron is added to a gaseous atom. Why 'gaseous' in both definitions? Why wouldn't liquids or solids work for these definitions?

 

10. Does an "isothermal" reaction exist, where in an isolated system, there is absolutely no heat released (not exothermic) or absorbed (endothermic)?

 

Organic Chem Questions

 

11. The addition of Br2 to an alkene leads to an intermediate carbocation (cyclic halonium ion), in this case, brominium. This brominium is further attacked by Br- in an 'anti' fashion which is a SN2 reaction. I don't understand how this can be considered an SN2 reaction

 

12. Addition of H2O to alkenes in an acidic condition. Why does it have to be acidic? Why can't the H from H2O just attack the alkene (why does the H+ attack the alkene beforehand to create the carbocation intermediate?)

 

Thank you SOOOO MUCH for anyone who can help me with any one of these questions!

[ghart]

This is the only question I can be confident about, off the top of my head:

 

5. Cortisol is released in response to stress in the human body. But one of its function is to reduce the immune system's potency. How would this be beneficial to the individual? Shouldn't the effect be opposite, and the body strengthen immune system to prevent any infections due to stress?

 

 

Ans: Remember cortisol isn't released to help with the immune system's response but rather to help increase blood glucose levels to help the individual in times of high stress. The reduction in the immune system's potency is due to the fact that the body is focusing so much attention on dealing with the stress that it cannot simultaneously maintain a potent immune system, thus increasing chances for infections. This is why too much stress isn't considered good.

[freebird]

Hi

 

I have quite a few questions about biology and general chemistry from studying the Kaplan Premier Program 2008/09 textbook.

 

1. Our body has four types of tissue: epithelial, connective, nervous, and muscle. But what kind of a tissue is the liver? Is it a blend of more than one tissue?

 

2. I only learned when genetic material and the cytosol divide during cell division (mitosis). But when do the cell organelles (mitochondria, Golgi etc.) divide and how?

 

3. Question regarding multiple births. Is it possible to have dizygotic (fraternal) fertilization in the beginning, followed by a zygotic split in just one of the two zygotes, so that there are triplets (two offspring that are identical, and one that is fraternal to the other two)?

 

4. I can't seem to understand the difference in functions between memory T cells and memory B cells in the human immune system. Are they simply different by their origin?

 

5. Cortisol is released in response to stress in the human body. But one of its function is to reduce the immune system's potency. How would this be beneficial to the individual? Shouldn't the effect be opposite, and the body strengthen immune system to prevent any infections due to stress?

 

6. What exactly is the difference between epinephrine and norepinephrine. And please, no copy and paste information from wikipedia. Tried it all.

 

7. How is the definition of "homozygous" any different from "true-bred"? If there are any differences, how are they different? (examples plz?)

 

8. Hardy-Weinberg Equilibrium Equation: p^2 + 2pq +q^2 = 1.

 

For p = 0.8 and q=0.2, the equation works when crossing two heterozygotes in a nonevolving population (no microevolution): The final gene frequencies add up to p = 0.8 and q = 0.2. But I tried this for crossing a homozygote dominant (p) with a heterozygote...and the frequencies CHANGED to p=0.9, and q=0.1. Shouldn't the gene frequencies remain constant for any random cross in a nonevolving population according to the HW equation?

 

General Chemistry questions

9. The ionization energy is defined as the energy required to completely remove an electron from a gaseous atom or ion. Electron affinity is defined as the energy change that occurs when an electron is added to a gaseous atom. Why 'gaseous' in both definitions? Why wouldn't liquids or solids work for these definitions?

 

10. Does an "isothermal" reaction exist, where in an isolated system, there is absolutely no heat released (not exothermic) or absorbed (endothermic)?

 

Organic Chem Questions

 

11. The addition of Br2 to an alkene leads to an intermediate carbocation (cyclic halonium ion), in this case, brominium. This brominium is further attacked by Br- in an 'anti' fashion which is a SN2 reaction. I don't understand how this can be considered an SN2 reaction

 

12. Addition of H2O to alkenes in an acidic condition. Why does it have to be acidic? Why can't the H from H2O just attack the alkene (why does the H+ attack the alkene beforehand to create the carbocation intermediate?)

 

Thank you SOOOO MUCH for anyone who can help me with any one of these questions!

 

1. The liver is an organ, and as with almost all organs, it contains a mixture of more than one tissue type.

 

2. Cell organelles divide during cytokinesis, in which the cytoplasm divides and separates. This occurs near the late stages of mitosis. Organelles generally do not divide during interphase, but there are exceptions. Mitochondria and photosynthetic organelles are the two of note.

 

3. Yes. Fraternal twins are created when two sperm fertilize two eggs. When the blastocyst embeds itself into the uterine wall, it can divide again and result in an identical twin.

 

4. I forgot, sorry.

 

5. Answered above.

 

6. The differences are too subtle for me to recall.

 

7. Homozygous refers to the alleles present, true-breeding refers to the offspring produced. True-breeding organisms for a specific trait are always homozygous for that trait. Essentially the two terms are synonymous, but they are used in different contexts.

 

8. Damn, sorry, it's 4:26 am, I must head off...

[kz87]

4. I can't seem to understand the difference in functions between memory T cells and memory B cells in the human immune system. Are they simply different by their origin?

 

I believe they differ mainly in the type of cell response they play a part in, T cell taking part in the cell-mediated response, and B-cells taking part in the humoral response.

 

6. What exactly is the difference between epinephrine and norepinephrine. And please, no copy and paste information from wikipedia. Tried it all.

 

Epinephrine and Norepinephrine differ in structure and in the receptors on which they act.

http://www.britannica.com/EBchecked/topic/190049/epinephrine

 

Can't help with the chemistry part, still haven't started preparing for it, but its about time i do, august is right around the corner!

[ballofnerves]

11. The addition of Br2 to an alkene leads to an intermediate carbocation (cyclic halonium ion), in this case, brominium. This brominium is further attacked by Br- in an 'anti' fashion which is a SN2 reaction. I don't understand how this can be considered an SN2 reaction

 

Yeah so you get a bromonium intermediate in which the bromine atom is bonded to both carbon atoms. Since the bromine atom has two bonds, it has a positive formal charge. Then the Br- attacks from the opposite side. Of course, carbon cannot be bonded to four things, so we must look for a leaving group. The Br+ that is part of the bromonium ion is a great leaving group since bromine is electronegative and desperately wants to get rid of its positive charge. If it takes the electrons from the bond between itself and the carbon atom, then it becomes very "happy" and is a great leaving group.

 

It is a little different from the typical SN2 reaction that you normally see. Instead of bromine leaving the molecule altogether, it remains bonded to another carbon in the molecule. But it does leave the carbon that is attacked by the nucleophile.

 

I hope that is clear...

[oohpsjin]

Thanks ghart freebird kz87 and ballofnerves!

Any clues to the other questions?

[LoMed]

4. I can't seem to understand the difference in functions between memory T cells and memory B cells in the human immune system. Are they simply different by their origin?

 

Just to add to another response, memory B cells produce antibodies and T cells are 'helper cells' that activate/aid other immune cells. Both are vital for a robust immune response.

 

 

6. What exactly is the difference between epinephrine and norepinephrine. And please, no copy and paste information from wikipedia. Tried it all.

 

Norepinepherine is a neurotransmitter and acts very quickly but briefly; whereas, epinepherine is a hormone and therefore, is slower to act but longer lasting. They both essentially do the same thing just by different avenues.

 

Cheers

[ballofnerves]

12. Addition of H2O to alkenes in an acidic condition. Why does it have to be acidic? Why can't the H from H2O just attack the alkene (why does the H+ attack the alkene beforehand to create the carbocation intermediate?)

 

Ok, back again...

 

So basically (no pun intended ) acid has to be present because if H+ were to leave H2O, you would be left with a hydroxide OH- ion. Hydroxide ions are very strong bases, much stronger than an alkene. Therefore, it would be much, much more likely for OH- to get back the H+, rather than the alkene attack the H+.

 

When acid is present, you get hydronium ions (H3O+). If H+ leaves hydronium, you get H2O and H+. H2O is not a very strong base, so it is more likely that this time, the alkene will attack the H+.

[Avinash]

Hi

 

12. Addition of H2O to alkenes in an acidic condition. Why does it have to be acidic? Why can't the H from H2O just attack the alkene (why does the H+ attack the alkene beforehand to create the carbocation intermediate?)

 

Thank you SOOOO MUCH for anyone who can help me with any one of these questions!

 

Just to add, the H+ from the H3O+ (as previously explained) does not "attack". Make sure you know your nucleophiles, in this case, the electrons from the double bond "attack" the H3O+, meaning the alkene is the nucleophile.

[gamma]

10. An isothermal system is one where there is no change in Temperature. Since temp for g-chem equates to change in avg. kinetic energy, there's also no change in kinetic energy. As a result, following from E = q + w, q = -w

 

great questions btw!

[HBP]

11. The addition of Br2 to an alkene leads to an intermediate carbocation (cyclic halonium ion), in this case, brominium. This brominium is further attacked by Br- in an 'anti' fashion which is a SN2 reaction. I don't understand how this can be considered an SN2 reaction

 

basically its an intramolecular SN2. the br2 adds to the opposite side (recall:inversion), while removing the bromonium bond. it's not really a substitution, more a new bond made old bond broken type thing.

[HBP]

12. Addition of H2O to alkenes in an acidic condition. Why does it have to be acidic? Why can't the H from H2O just attack the alkene (why does the H+ attack the alkene beforehand to create the carbocation intermediate?)

 

I don't think water is acidic enough to protonate an alkene. Just think about it qualitatively, if you add water + alkene would you expect an alcohol? Or would you expect a layer of polar/layer of non-polar (no rxn).

 

Remember, whenever something loses an H, it must have it's conjugate base to be stable on it's own. Think of H-Br, when H leaves to protonate the alkene, Br- is stable on it's own. OH- isn't (correct me if I'm wrong, but you'll rarely find OH- on it's own... unless the rxn is base catalyzed), much better to have H20 on it's own after H+ protonates.

[princessflower24]

4. I can't seem to understand the difference in functions between memory T cells and memory B cells in the human immune system. Are they simply different by their origin?

 

Just to add to another response, memory B cells produce antibodies and T cells are 'helper cells' that activate/aid other immune cells. Both are vital for a robust immune response.

 

 

6. What exactly is the difference between epinephrine and norepinephrine. And please, no copy and paste information from wikipedia. Tried it all.

 

Norepinepherine is a neurotransmitter and acts very quickly but briefly; whereas, epinepherine is a hormone and therefore, is slower to act but longer lasting. They both essentially do the same thing just by different avenues.

 

Cheers

 

 

Please note that BOTH NOREPINEPHRINE and Epinephrine are hormones. Norepinephrine though, can act as a neurotransmitter as well.

[The Law]

4. I can't seem to understand the difference in functions between memory T cells and memory B cells in the human immune system. Are they simply different by their origin?

 

Just to add to another response, memory B cells produce antibodies and T cells are 'helper cells' that activate/aid other immune cells. Both are vital for a robust immune response.

 

To add to this too, the response of B-cells to produce antibodies is known as a hummoral response (i.e. "Into the blood" because they secrete antibodies into the blood). When a B-cell encounters an antigen, it can become activated by joining up with a helper T-cell. When they join together, some B-cells will proliferate into plasma cells that secrete antibodies to fight the infection, while some will become "memory B cells." Memory B-cells are used in the case of re-infection, and are able to mount a much quicker response when activated than the primary response that was happening when the memory cells were formed.

 

T-cells are not only helper cells. There are two major types of T-cells, Cd4 and cd8. Cd4 cells are known as helper cells because they help to activate other immune cells to perform their function in fighting an infection. Cd4 cells activate B-cells (as just described earlier), and they can also activate cytotoxic T-cells (aka. cd8 t-cells). Cytotoxic T-cells hunt throughout the body to find infected cells and destroy them. Some T-cells form "memory T-cells" and again, in case of reinfection allow for a much quicker secondary immune response.

 

 

General Summary:

*T-Cell types are cd4 (helper), cd8 (cytotoxic)

 

*Cd4 (helper) T-cells activate B-cells and Cd8 (cytotoxic) T-cells

 

*Cd8 cells hunt the body to find infected/cancerous cells and kill them

 

*There are other forms of T-cells too, google and you can learn more about natural killer T-Cells, regulatory t-cells, and gamma/delta t-cells

 

*B-cells start as naive B-cells before activated, then proliferate into plasma cells that secrete antibodies (when activated by a Cd4 T-cell) or into memory B-cells (for quicker response during reinfection)

 

*Memory T-cells are just like memory B-cells (allow for quicker response to reinfection)

[goose]

Hi

 

 

10. Does an "isothermal" reaction exist, where in an isolated system, there is absolutely no heat released (not exothermic) or absorbed (endothermic)?

 

 

Careful in the distinction between isothermal and adiabatic processes. The situation you've described (in which there is no heat exchanged between the system and surroundings) is adiabatic. It's in this case that Q = 0 and U = -W.

 

Isothermal processes, like gamma mentioned, are processes in which the temperature of the system remains constant - it doesn't have anything to do with the exchange of temperature with surroundings. In fact, most isothermal processes require heat exchange with the surroundings to release heat produced or absorb heat lost to remain at a constant temperature.