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2011-11-28 21:07:47
gene expression protein synthesis

Ch 18 Gene Expression and Protein Synthesis
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  1. The central dogma of molecular biology
    The dogma states that the information contained in DNA molecules is transferred to RNA molecules, and then from the RNA molecules the information is expressed in the structure of proteins.

  2. Gene expression
    The activation of a gene to produce a specific protein; it involves both transcription and translation.
  3. Transcription
    The process in which information encoded in a DNA molecule is copied into an mRNA molecule.
  4. Translation
    Translation is the process by which the genetic information preserved in the DNA and transcribed into the mRNA is converted to the language of proteins--that is, the amino acid sequence.

    Three types of RNA (mRNA, rRNA, and tRNA) participate in the process.
  5. Template strand
    The strand of DNA that serves as the template during RNA synthesis
  6. Coding Strand
    The strand of DNA with a sequence that matches the RNA produced during transcription
  7. What are the three kinds of polymerases that catalyze transcription in eukaryotes?
    1. RNA polymerase I (pol 1) catalyzes the formation of most of the rRNA

    2. Pol II catalyzes mRNA formation

    3. Pol III catalyzes tRNA formation as well as one ribosomal subunit and other small regulatory RNA types, like snRNA.
  8. DNA is highly condensed in the chromosomes. What is the sequence of events that enables the transcription of a gene to begin?
    First, binding proteins must make the portion of the chromosome where the gene is less condensed and more accessible.

    Second, the helicase enzyme must unwind the double helix near the gene.

    Third, the polymerase must recognize the initiation signal on the gene.
  9. Codon
    The sequence of three mucleotides in messenger RNA that codes for a specific amino acid.
  10. Genetic code
    The sequence of triplets of nucleotides (codons) that determines the sequence of amino acids in a protein.
  11. There are 20 amino acids in proteins. How many possible combinations of four bases into triplets (codons) are there?
  12. What three codons are "stop signs"?
    • UAA
    • UAG
    • UGA

    They terminate protein synthesis
  13. What codon is the "Start sign"? What else does it do?
    The initiation sign is AUG, which is also the codon for the amino acid methionine.
  14. The amino acid Arginine is represented by the codon CGU. What is its anticodon?
  15. DNA is generally read 5' to 3' what is on the 5' end? What is on the 3' end?
    • 5' has a free phosphate group terminous
    • 3' has a free hydroxyl group terminous
  16. What are the four major stages in protein synthesis?
    1. Activation: The process by which an amino acid is bonded to an AMP molecule and then to the 3' -OH of a tRNA molecule.

    2. Inititation: The first step in the process whereby the base sequence of a mRNA is translated into the primary structure of a polypeptide.

    3. Elongation: The phase of protein synthesis during which activated tRNA molecules deliver new amino acids to ribosomes where they are joined by peptide bonds to form a polypeptide.

    4. Termination: The final stage of translation during which a termination sequence on mRNA tells the ribosomes to dissociate and release the newly synthesized peptide.
  17. An error in the copying of a sequence of bases is called a
  18. Mutagen
    A chemical substance that induces a base change or mutation in DNA
  19. What is gene therapy?
    Gene therapy is a technique whereby a missing gene is replaced using a viral vector.

    In ex vivo gene therapy, cells are removed from a patient, given the missing gene, and then the cells are given back to the patient.

    In in vivo therapy, the patient is given the virus directly.
  20. Does the term gene expression refer to transcription or translation?
    Gene expression refers to both processes, transcription and translation
  21. Where does most of the translation occur in a eukaryote cell?
    Protein translation occurs on the ribosomes.
  22. What is the role of helicase in transcription?
    Helicases are enzymes that catalyze the unwinding of the DNA double helix prior to transcription. The helicases break the hydrogen bonds between base pairs.
  23. Which end of the DND contains the termination signal?
    The termination signal is at the 5' end of the template strand that is being transcribed.

    It can also be said to be at the 3' end of the coding strand.
  24. Where are the codons located?
    On the messenger RNA.
  25. What are the ribosomal subunits for eukaryotic translation?
    The main subunits are the 60S and 40S ribosomal subunits, although these can be dissociated into even smaller subunits.
  26. Does the term gene expression refer to

    A. transcription
    B. transcription plus translation
    C. translation
    B. transcription and translation
    (this multiple choice question has been scrambled)