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  1. K

    1 hard(? ) Biology Question HELP! :/

    Yes, it is a consequence of the reaction mechanism. The point of the "evolutionary limitation" is that evolution works with what it's got. What we -have- is a 5' -> 3' elongation mechanism, not a 3' -> 5' one. So this entire machinery surrounding Okazaki fragments gets invented to deal with...
  2. K

    1 hard(? ) Biology Question HELP! :/

    Yeah, pretty much. The helicase unwinds the DNA, resulting in two single strands of DNA running in opposite directions at the fork. If DNA synthesis can only proceed in one direction, then only one of these can be continuously synthesized, since the other strand must be being unwound in the...
  3. K

    <HELP!> One question about Meselson-Stahl experiment

    Could you explain why you think your answer is right? More generally, what should happen after each replication (first, second) under each of the three hypotheses? That's only 6 things, you should be able to do that in one post.
  4. K

    Chymotrypsin mechanism?

    Two comments/questions: Why do you believe that the O of Ser195 would be nucleophilic before its proton was partially abstracted by His57? Why do you believe that the substrate would remain in the reaction center if it is no longer involved in the reaction after step c?
  5. K

    The difference between structural unit and repeating unit?

    Polyethylene teraphthalate has two structural units but only has one repeating unit. Structural units are substructures that are derived directly from the inputs. If you call the repeating unit [-R-], then you can write a polymer as -[-R-]-n. So while polyethylene teraphthalate has the...
  6. K

    How to find frequency of gametes

    This isn't about Punnett squares. Punnett squares are for predicting the genetic makeup of progeny, when given gametic frequency. You are given a recombination frequency and are asked to find gametic frequencies. This is about homologous recombination.
  7. K

    Effect of pH on enzyme activity

    You're already explained what -happened- just fine. What happened to the enzyme in each test tube? Also, this should be in the homework forum.
  8. K

    Correlation between Snowball Earth and Cambrian Explosion

    There are -a lot- of theories regarding the matter, and the murkiness of the issue is complicated somewhat by the uncertainty of estimates regarding the exact dates during which the Earth was entirely covered in ice. We're much more certain about the dates for the radiation of metazoa than we...
  9. K

    Would exonic primers affect gDNA amplification?

    I can't think of a reason why any given primer should work only for cDNA. Maybe the reason why you're having trouble with the genomic DNA amplification has to do with other possible annealing sites on the genomic DNA? I had this problem before. If you have upstream/downstream genetic...
  10. K

    Actin Confusion

    Perhaps this website might help you? http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/actin.htm
  11. K

    Chromosomal Crossing Over

    The short answer is yes, the chromatin DNA must unwind from its nucleosome-bound state in order to engage in homologous recombination.
  12. K

    State 4 Respiration

    It would help if you copied the entire question. I don't understand the ADP addition experiment from what you copied alone.
  13. K

    Hey, I'm helping a HS student write a research abstract

    Hey, I wish I'd thought of doing this when I was trying to write papers. I do have a few suggestions, some requests for clarification, and at least one actual bone to pick. Minor stuff first: Do not capitalize cis-3-Hexenal. Do use consistent formatting in your introduction of supplementary...
  14. K

    Color vision, and seeing violet

    So I looked up some papers which had better diagrams, and you're absolutely right, the L pigment -does- have another peak inside the visible. Both the L and the M secondary peaks are right underneath the primary peak of the S, and the S pigment has a secondary peak even further into the shorter...
  15. K

    Color vision, and seeing violet

    So I read up some on Wikipedia, and I came up with a partial explanation. Violet and purple are not the same thing. Violet is a "spectral color," meaning that there is monochromatic light of a certain wavelength that looks violet. "Purple," on the other hand, corresponds to no single...
  16. K

    If we could see multiple octaves of light, would we perceive a cycle of colors?

    Hm. It seems to me that the "octaves" idea actually wouldn't work, and here's why I think so; The rhodopsin-based pigments work because a cis-trans double-bond isomerization in the rhodopsin center causes a conformational change in the protein, which gets converted into a membrane potential...
  17. K

    (Biology) Cell Transport Methods & Mitosis in Animals

    Anyhow, to the coursework help itself: The transport questions As you know, the cellular membrane in eukaryotes and bacteria consists of a phophoslipid bilayer. The bilayer has a polar-nonpolar-polar structure, and since "like dissolves like," the stable nonpolar layer in the middle functions...
  18. K

    Structural isomers of C4H8Br2

    Oh, you're right. Structural isormers, not stereoisomers. In that case, I think you've got them all.
  19. K

    Structural isomers of C4H8Br2

    Don't forget chirality.
  20. K

    Alkene diastereomers

    I don't quite understand the system you're asking about. I can only assume you made a typo whe you wrote "we reacted maleic acid with a temporary carbocation to see whether the product would be maleic acid or fumaric acid." Could you write out the full reaction? (no need to try including...
  21. K

    Nucleophilic substitution question!

    Don't forget resonance, which can confer additional stability to carbocations. This effect is often stronger than that of substitution.
  22. K

    OChem I Sn1 Sn2 Reactions

    The whole reason why tertiary/secondary/primary substitution level matters is that it stabilizes the intermediate carbocation, i.e., substitution level matters on the electrophile, not the nucleophile. It doesn't matter whether the nucleophile is tertiary or primary. CH3CH2-Br is...
  23. K

    Percent Composition & Finding Formula - Chemistry

    Generally, if you did the problem correctly, a pretty obvious and easily recognizable ratio of small whole numbers will turn out. Just do it and then see. Admittedly, I always just used the ->frac command on my calculator.
  24. K

    Acid-base equlibrium

    If you write out all of the equations you have and plug them into each other, you'll see that [H+] is not equal to [A-]. Your assumption that they are equal is throwing you off. Also don't forget that the volume of the entire solution changed because you added the NaOH solution.
  25. K

    Percent Composition & Finding Formula - Chemistry

    Convert everything to moles. Find the ratio of (moles sulphur consumed) to (moles iron consumed). That should give you the atomic ratio of sulphur to iron in the sulphide, which translates easily to a formula. In general, "convert everything to moles" is a good first step.
  26. K

    Biology lab help needed!

    Just write out the entire system. Your main reaction is H2O2 ----> H2O + O2 catalyzed by peroxidase. But O2 is invisible, so we add an indicator, so that when O2 is produced, it further undergoes the reaction O2 + guaiacol ---> something brown and you can measure the brown-ness...
  27. K

    Another bio lab question!

    Cyanide acts upon the electron transport chain, so fermentation (which by definition does not involve vectoral metabolism via the electron transport chain) cannot possibly be affected by cyanide (assuming that the only mechanism of action of cyanide is upon the electron transport chain.) In...
  28. K

    Complex solubility problem

    Are you sure that you're supposed to be dealing with Cr(II) species at all in this problem? Because it looks to me like you may have copied some equations wrong: Cr2+ + 2 OH- <==> [Cr(OH)2]+(aq) K2 = 10^18.3 Cr2+ + 3 OH- <==> Cr(OH)3 (aq) K3 = 10^24.0 Those equations aren't charge-balanced...
  29. K

    Stat. Mech: energy-temperature relation of a perfect classical gas

    Those were very helpful explanations of why my original statement of the problem made no sense. I still don't completely understand why g(E) = cE^(1/2); everything follows after that, though. Importantly, I understand how the multiple-particle models change the final result by forcing...
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