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Winter Biology 2012
Practice Exam 1
Notes: A suggestion for how long an answer I am looking for is found at the end of each relevant question. In some cases 1 sentence could actually be one or a few words. Try to take this exam in 50 min it is about the same length as the real exam. Good luck! 1 (5 pts) Provide the chemical formula for stable gases made by combining each of the following atoms (Oxygen is shown as an example):
Oxygen! (O)! Neon! (Ne)! Chlorine! (Cl)!
!
!
!
! O2!
Nitrogen! (N)! Fluorine! (F)! Argon! (Ar)!
!
!
!
2
(4pts) What is a buffer? Why does buffering capacity depend on the buffer concentration (~2 sentences).
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(4 pts) Many biological structures are composed of smaller units assembled into more complex structures, and having functions based on their structural organization. For enzymes, describe the smaller units, how they are assembled into the larger structures, and one major function of these larger, organized structures (2-3 sentences).
Practice Exam 1
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(9 pts) Using the list below, describe the position (i.e., within the protein core or on the surface) of the amino- and carboxy-terminal ends of the proteins shown below when these proteins form a multimer in an aqueous solution. In addition, indicate whether the protein has the potential (yes/no) for forming intramolecular and/or intermolecular disulfide linkages.
Nonpolar Amino Acids (hydrophobic) Alanine, Ala Leucine, Leu Glycine, Gly Methionine, Met Isoleucine, Ile Phenylalanine, Phe Polar Amino Acids (hydrophilic) Asparagine, Asn Glutamine, Gln Cysteine, Cys Serine, Ser Electrically Charged Amino Acids (hydrophilic) Arginine, Arg Glutamic Acid, Glu Aspartic Acid, Asp Histidine, His
Proline, Pro Tryptophan, Trp Valine, Val Threonine, Thr Tyrosine, Tyr Lysine, Lys
4a. N-Met-Gly-Ile-Pro-Cys-Gly-Tyr-Gly-Ser-Ile-Ala-Lys-Glu-Asp-C N terminus _______ C terminus _______ Intra-disulfide ____ Inter-disulfide ____ 4b. N-Cys-Arg-His-Ser-Ala-Gly-Pro-Pro-Ile-Gly-Ser-Asp-Cys-Gly-C N terminus _______ C terminus _______ Intra-disulfide ____ Inter-disulfide ____ 4c. N-Ser-Tyr-Thr-Asp-Gly-Pro-Gly-Ala-Leu-Ile-Asp-Lys-Arg-Gln-C N terminus _______ C terminus _______ Intra-disulfide ____ Inter-disulfide ____ 5 (3pts) Why is RNA favored over DNA and proteins as the earliest life form? (1-2
sentences)
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(5 pts) If you had a mutation in your cells to inactivate either DNA polymerase III (used for leading strand synthesis) or DNA polymerase I (also used for lagging strand synthesis), which would you prefer? Why? (~2-3 sentences)
Practice Exam 1
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(6pts) The results of the classic Meselson & Stahl experiment are shown in the figure above. If the experiment had been carried out for four generations instead of two: a) What would be the fraction of high-density (15N) DNA ___ strands? b) What would be the fraction of lower-density (14N) DNA strands? ___ c) What would be the fraction of intermediate-density DNA strands? __ Using radioactively labelled single-strand-binding proteins (SSBPs), scientists were able to discern that one parental strand of replicating DNA had more SSBPs bound than the other strand of parental DNA. a) (3pts) Which strand was this? (circle one) Leading Strand Lagging Strand
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b) (3pts) How do you know? (~1 sentence)
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(8 pts) Use the following descriptions of human genes to answer the questions below. Gene K is transcribed constitutively and is never translated. Gene L is transcribed very rarely and has a very long poly-A tail. Gene M is transcribed whenever the human is exposed to direct sunlight. Gene O is transcribed at constant low levels. It creates a protein with that is phosphorylated, but phosphorylated only at night. Pick the correct gene or genes for each question. Example: Which gene is most likely to help guard against skin cancer? M a. Which gene(s) are most likely to create tRNA? ______ b. Which gene(s) are transcriptionally regulated? ______ c. Which gene(s) have a promoter region? ______ d. Which gene(s) creates a protein that is regulated very quickly? _______
Practice Exam 1
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(4 pts) Are sigma factors required throughout the transcription process? Why or why not? (~2 sentences)
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(4 pts) Why do some changes in a gene sequence change the functioning of a protein and others do not? (~ 1-2 sentences)
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(4 pts) Why is the genetic code considered to be "degenerate"? (~1-2 sentences)
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A DNA change from A G is a transition. A change from A C is a transversion. a) (3pts) Changes in the wobble position of codons are most likely to be: (Circle one) transitions transversions
b) (3pts) How do you know? (~1 sentence)
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(6 pts) Mutations resulting in a Glu to Gly substitution has occurred in the sequence of a protein. What is the most likely sequence for the original Glu and resulting Gly codons? Explain your answer (~2 sentences) Amino acid Glu Val Lys Gly DNA triplets that code for these amino acids CTT or CTC CAA or CAG or CAT or CAC AAA or AAG GGT or GGC or GGA or GGG
Practice Exam 1
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(8 pts) If you had a bacteria strain with mutant LacI so that it did not produce any product, would the operon be producing functional beta-galactosidase when grown in glucose? If so, at high levels or very low levels? Explain your answer in terms of CAP activation and binding, RNA polymerase activation and binding, and repressor activation and binding. (~2-3 sentences)
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(8 pts) Carbohydrates, fats and water are able to store different amounts of chemical energy. What is the rank order of their potential energies? What determines this rank order? (~ 2 sentences)