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Homework Help: Can I get my intro Bio problems checked?

  1. Sep 14, 2007 #1
    1. The problem statement, all variables and given/known data

    I have a list of 25 questions to answer. For the most part I answered all of them and would like to get my answers checked. I believe they are correct, but would like a second opinion on my answers (my answers are the underlined parts of the sentences). Here are the questions, followed by the answers I have chosen:

    2. Relevant equations


    3. The attempt at a solution

    1. The reason cellulose is better suited than starch to be the major component of the plant cell wall is because cellulose molecules form many hydrogen bonds to each other.

    2. Polypeptides tend to be the workhorse of the cell.

    3. The primary difference between a stem cell and a progenitor cell is stem cells can give rise to many different types of differentiated cells while progenitors can only give rise to one type of differentiated cell.

    4. In proteins, hydrogen bonding between the hydrogen (of the amino group) and oxygen (of the carboxylic acid) that are part of the amino acid backbone is primarily responsible for the secondary layer of structure.

    5. You are studying a cellular enzyme involved in breaking down fatty acids for energy. Looking at the R groups of the amino acids, non-polar amino acids would occur in the aprts of the enzyme that interact with the fatty acids.

    6. 99 water molecules are required for the synthesis of an amylose polymer that is comprised of 100 glucose monomers.

    7. Cysteine, serine, and threonine are examples of polar (uncharged) amino acids.

    8. Carbon can combine with 3 hydrogen atoms and 1 hydroxyl group to generate methanol. Given that oxygen is more electronegative than carbon or hydrogen (carbon and hydrogen electronegativities are very close to equal), polar covalent, nonpolar covalent, and hydrogen bonds are expected to be observed in a container of methanol.

    9. If an atom has an atomic mass of 20, the number of electrons that are most likely associated with this atom (assuming the atom has a net charge of zero) is 10.

    10. Hydrogen bonds are responsible for the cohesive properties of water.

    11. A good example of how form correlates with function is the muscle cells of a long distance runner have lots of mitochondria.

    12. The primary difference between Gram positive and Gram negative bacteria is that gram positive has one lipid bilayer in the outer membrane/cell wall while Gram negative has two lipid bilayers.

    13. While working with B-galactosidase, an enzyme that catalyzes a reaction that changes the X-gal compound from being essentially colorless to dark blue, you accidentally heat and denature it. To avoid trouble with your adviser, you attempt to renature the enzyme by slowly cooling it down. You add X-gal to the cooled enzyme and you get a light blue color instead of the usual dark blue. The most likely explanation for this is that you have completely renatured the enzyme.

    14. A secreted protein has a zip code or sequence that directs it to enter the secretory pathway (ER and Golgi). What might happen if you artificially added this zip code to a protein that normally functions in the cytoplasm is it would stay in the cytoplasm because the zip code is not the right one for that protein.

    15. Based on what is known about the molecular structure of RNA (and how it compares to DNA), it can not be predicted that the 2 RNA strands with complementary sequences should be able to form double stranded duplexes.

    16. The following is not a "rule" that drives protein folding: the R groups of oppositely charged amino acids often form ionic bonds (generally on the exterior of the protein).

    17. Lipids are a macromolecule that is not a polymer.

    18. A short oligonucleotide has the sequence 5'-TATTGGCTA-3'. The sequence of the complementary piece of DNA is 5'-TAGCCAATA-3'.

    19. The following is not one of the primary differences between eukaryotes and prokaryotes: eukaryotes have chloroplasts while prokaryotes have thylakoid membranes.

    20. LiCl is a molecule. Li and Cl atoms are held together by ionic bonds.

    21. The octet rule says that atoms tend to gain, lose, or share electrons so as to ahve eight electrons in their outer electron shell. Given what you know about the chemical formula for the phosphate functional group, you can say that the octet rule is disobeyed in this case.

    22. The notion that the more highly ordered molecules are in a substance, the more likely it is to be solid or more firm is exemplified by ice, cellulose, NaCl, saturated fatty acids, and unsaturated trans fats.

    23. The pH of a solution is 3. The molar concentration of the hydroxyl ions in the solution is 10^-11 M.

    24. Phosphorus has an atomic number of 15. 5 electrons are likely to be in the valence electron shell.

    25. The 3 carbon backbone of a fat molecule is glycerol.

    Thank you!
  2. jcsd
  3. Sep 22, 2007 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    #2 is probably looking for an organelle.
    You also will want to rethink #13.
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