Quiz #1

Biochemical Engineering

Fall 2009


Instruction

You may use one 8.5x11 sheet of notes, but nothing else (no calculators, laptop computers, etc). Any act of academic dishonesty will not be tolerated.
  1. (5 pts.) Honor Codes and Ethics. Circle either "T" or "F" to indicate whether the following statements are true or false for this class.

    1. You may discuss how to solve a homework assignment with your classmates. |T|F|

      Solution:

      True. (Because I said so.)

    2. If convicted of academic dishonesty, you will get a grade of "F" for the course. |T|F|

      Solution:

      False. (You get a grade of "XF" meaning failure due to academic dishonesty.)

    3. You may download a Mathcad file from the class web page, load it in Mathcad, modify it a bit to answer the homework problem on hand, and turn it in for credit. |T|F|

      Solution:

      True. (The web pages, as long as they are equally available to everyone in the class, are for you to use as you see fit, but you must give proper credit to the source, as is always the case. On the other hand, it is not ok to receive a Mathcad file from your friend, move things around a bit, and turn it in for credit, because that is basically copying and is unfair to others who do not have access to the same information. If you work together with your classmate to produce one outcome, you need to credit that person; not giving proper credit means you pass off work as your own.

    4. If you observe a violation of the honor code, you should report the incident to the Student Honor Council. |T|F|

      Solution:

      True. (It is everyone's responsibility, not just the instructor's.)

    5. Your instructor determines whether or not you have cheated. |T|F|

      Solution:

      False. (Your are innocent until proven guilty, and your fellow students in the Student Honor Council are the judges of your innocence.)

  2. (40 pts.) Briefly describe/contrast the following concepts/terms.

    1. Biochemical Engineering and Chemical Engineering

      Solution:

      Biochemical engineering is the part of chemical engineering that deals with biological components (biomolecules, biopolymers, enzymes, cells). Concepts in transport, thermodynamics, reaction, separation, unit operation, etc. remain largely unchanged.

    2. Life & Organism

      Solution:

      Life: Having the ability to reproduce on its own. Organism: a living entity, i.e., an entity that has the ability to reproduce on its own.

    3. Species. (What makes a species a species?)

      Solution:

      Species: A group of organisms that can interbreed with other members of the same species. A new organism (like a liger) that cannot propagate is not a new species. A mutant that can propagate with the wild type from which it evolved is not a new species.

    4. Four main types of biopolymers and classify them as "structural and energy" or "informational and regulatory".

      Solution:

         Fats/lipids, polysaccharides         ... structural/energy
         Protein, polynucleotides (DNA & RNA) ... informational/regulatory
      

    5. Three common configurations to pack a large surface area in a compact manner

      Solution:

        stacked plates
        spiral wound (or pleated)
        hollow fiber (shell-and-tube)
      

    6. Major types of biological recognition exploited in biosensor design

      Solution:

         Enzyme-substrate
         Antibody-antigen
         DNA-DNA, DNA-RNA
         Receptor-ligand
      

    7. List two common reasons for enzyme immobilization.

      Solution:

        reuse expensive enzyme
        keep product free of contamination from enzyme
      

    8. Give two methods by which an enzyme may be entrapped. List one major advantage and one major disadvantage of each method.

      Solution:

                             advantage   disadvantage
        ---------------------------------------------------------------
        polyacrylamide gel   permanent   toxicity & thermo inactivation
        calcium alginate     mild        soft & disintegration of gel
      

  3. (25 pts.) Isoelectric Point.

    1. Briefly describe "isoelectric point".

      Solution:

      The pH at which a zwitterion (such as a protein) has no net charge (i.e., neutral), thus, will not migrate in an electric field.

    2. Briefly describe "isoelectric focusing".

      Solution:

      Electrophoresis on a gel that has a pH gradient. The electric field drives the charged protein molecules to a pH environment until the protein molecules has no net charge and stops migrating.

    3. Lysine has an amine side group R that can be protonated. Its dissociation constants are given below.
        Lysine: H2N-(CH2)4-CH(NH2)-COOH
        pK1 (for -COOH) = 2.18
        pK2 (for -NH2)  = 8.95
        pKR (for R)     = 10.53
      
      Based on these dissociation constants, give equation(s) that lets you calculate the isoelectric point.

      Solution:

        Lysine can take on four forms: A++, A+, A, A-
          at     pH<pK1:  +H3N-(CH2)4-CH(NH3+)-COOH  abbreviated as A++
          at pK1<pH<pK2:  +H3N-(CH2)4-CH(NH3+)-COO-  abbreviated as A+
          at pK2<pH<pKR:  +H3N-(CH2)4-CH(NH2)-COO-   abbreviated as A
          at    pKR<pH:    H2N-(CH2)4-CH(NH2)-COO-   abbreviated as A-
      
        pK1 (for -COOH) = 2.18  = [A+][H+]/[A++]
        pK2 (for -NH2)  = 8.95  = [A][H+]/[A+]
        pKR (for R)     = 10.53 = [A-][H+]/[A]
        conservation of species :  [A++]+[A+]+[A]+[A-]=[A]total
        isoelectric point:        2*[A++]+[A+]=[A-]
      
        Solve the above 5 equations for 5 unknowns: [A++], [A+], [A], [A-], [H+]
      

    4. Give a rough estimate of lysine's isoelectric point without solving the above equations.

      Solution:

      Half way between pK2 and pKR.

        pKI = (pK2+pKR)/2 = (8.95+10.53)/2 = 9.74
        The reported value is pKI=9.59
      

  4. (25 pts.) GATTACA.

    1. In the movie Blade Runner, a creator of an organism signs his name in his creation's DNA. You modify the DNA in an organism, watermark the piece of DNA you have created with a unique tandem repeating series of "GATTACA" to discourage others from copying/stealing your creation, and patent it. You submit your competitor's organism to a DNA sequencing outlet, which promptly reports the sequence back to you. A search finds no "GATTACA" in the reported DNA sequence of your competitor's organism. However, there is a tandem repeat of "TGTAATC", which your patent attorney assumes to be your competitor's watermark and concludes that there is no foul play because your competitor's organism contains a different DNA sequence from yours. Should you press your attorney to pursue infringement charges? Briefly explain why to your attorney.

      Solution:

      You competitor copied your creation. The complementary sequence of 5'-GATTACA-3' is 5'-TGTAATC-3'.

        5'-GATTACA-3'
        3'-CTAATGT-5'
      

    2. During a trial, you are asked the question of the likelihood of finding the sequence "GATTACA" in a random piece of DNA of 1000 base pairs. What is the probability?

      Solution:

        expected number of occurrences = (1000-7+1)/47  (roughly 1000 in 16K, or 6%)
        More precisely...
        probability of finding GATTACA starting at base #1 = 1/47 = 4-7
        probabiliy of not finding GATTACA starting at base #1 = 1-4-7
        probabiliy of not finding GATTACA starting at base #2 = 1-4-7
        probabiliy of not finding GATTACA starting at base #1 through base #994 = (1-4-7)994
        probabiliy of finding GATTACA somewhere starting at base #1 through base #994 = 1-(1-4-7)994 = 6%
      

    3. You perform chemical analysis on the tandem repeat "GATTACA" section of DNA taken from your organism. What is the composition (in terms of weight fraction of A, T, C, & G)?

      Solution:

        GATTACA
        CTAATGT
      
        base   relative     mole    molecular    relative      wt
                 mole     fraction     wt           wt      fraction
        ------------------------------------------------------------
          A       5         5/14        MWA       5*MWA      5*MWA/Σ
          T       5         5/14        MWT       5*MWT      5*MWT/Σ
          C       2         2/14        MWC       2*MWC      2*MWC/Σ
          G       2         2/14        MWG       2*MWG      2*MWG/Σ
        ------------------------------------------------------------
        total    14          1                     Σ           1
      

    4. Give the number of possible hepta-peptides (i,e., peptides with 7 monomer units).

      Solution:

      There are 20 possible amini acid at each position.

        20x20x20x20x20x20=207=27*107 (over a billion)
      

    5. As an expert witness in a trial case, you need to testify the likelihood of finding the sequence "GATTACA" anywhere within a random protein of 100-peptide. What is the probability?

      Solution:

        expected number of occurrences = (100-7+1)/207  (roughly 100 in a billion)
        More precisely...
        probabiliy of finding GATTACA starting at peptide #1 = 1/207 = 20-7
        probabiliy of not finding GATTACA starting at peptide #1 = 1-20-7
        probabiliy of not finding GATTACA starting at peptide #2 = 1-20-7
        probabiliy of not finding GATTACA starting at peptide #1 through peptide #94 = (1-20-7)94
        probabiliy of finding GATTACA somewhere starting at base #1 through base #94 = 1-(1-20-7)94 = 7x10-8  (roughly 100 in a billion)
      

  5. (15 pts.) Two-Step Enzyme Catalysis Reaction. The following two-step reaction converts substrate S1 to product P, with each step catalyzed separately by E1 and E2.
      S1 --> S2 --> P
    
    You design an enzyme E by combining the active sites of both E1 and E2 into one single protein. E can complex with S1 and S2 to form ES1 and ES2, respectively. ES1 and ES2 can further complex with S2 and S1, respectively; however, only ES2 can lead to the final product P.
               K1        K3
      E + S1 <---> ES1 <---> E + S2
               K2       k2
      E + S2 <---> ES2 ---> E + P
                K2
      ES1 + S2 <---> ES1S2
                K1
      ES2 + S1 <---> ES1S2
    
    Based the above mechanism, derive the reaction rate v2 (which is the rate of formation of product P. Likewise, derive the reaction rate v1 (which is the rate of formation of intermediate S2). List only applicable equations and the variables to be solved for, but do not actually solve them.

    Solution:

      definition of rate:             v1=k3*ES1-k-3*E*S2-k2*E*S2+k-2*ES2-k-2*ES1*S2+k-2ES1S2
      definition of rate:             v2=k2*ES2
      conservation of enzyme species: E0=E+ES1+ES2+ES1S2
      equilibrium assumptions:        K1=E*S1/ES1
                                      K2=E*S2/ES2
                                      K1=ES2*S1/ES1S2
      (Or, in lieu of the above 3 equilibrium assumptions, 3 quasi-steady-state assumptions on intermediate species: d(ES1)/dt=0, d(ES2)/dt=0, d(ES1S2)/dt=0)
      Solve the above 6 equations for 6 unknowns: v1, v2, E, ES1, ES2, ES1S2
    
    Note that the following equilibrium relationship is redundant; it is not an independent equation and should not be included along with others that have already been included.
      K2=ES1*S2/ES1S2
    


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Biochemical Engineering -- Quiz #1
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Nam Sun Wang
Department of Chemical & Biomolecular Engineering
University of Maryland
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