ch 22

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doncheto
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251585
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ch 22
Updated:
2013-12-07 22:50:45
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translation
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tranlation
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  1. Explain the meaning of genetic code and codon
    and be able to use a “dictionary” similar to the one in Fig. 21-6 or Slide 1.
    •Nearly) universal genetic code

    • –61 codons
    • encode for 20 a.a. (redundant or degenerate, i.e.
    • > 1 triplet/codon for 1 a.a.)

    –Only Met and Trp are non-degenerate

    –Start codon: AUG

    –3 stop codons: UAA, UAG, UGA

    • –Third (usually) nucleotide differ
    • in codons that specify for the same amino
    • acid
  2. What does it mean to say that the genetic code is degenerate or redundant?
    When there are more than one codon for an animoacid
  3. Which codon is the start codon? Which ones are stop codons?
    • =Start: AUG
    • –3 stop codons: UAA, UAG, UGA
  4. Is the mRNA code overlapping or nonoverlapping? What would be the effect of
    insertion of a single nucleotide on the protein encoded in either case?
    None overlapping. Mutant codes will be created.
  5. How many reading frames does each transcript have? What can cause a frameshift?
    • Only one reading
    • frame encodes the desired protein.
    •  Insertion or deletion
    • of nucleotides in numbers other than multiples of three causes frameshift in translation.
  6. Know the general structure of a ribosome.
    • –rRNAs form
    • core: give structure, position tRNA on mRNA, catalyze peptide bond
    • formation

    –Proteins form surface: stabilize core

    –Small subunit: matches tRNAs to codons

    • –Large subunit; forms peptide bonds (contains peptidyl transferase,
    • e.g. of ribozyme)

    • –mRNA binding site
    • –A-site (aminoacyl-tRNA)
    • –P-site (peptidyl-tRNA)
    • –E-site (exit)
  7. What are the functions of the rRNAs, ribosomal proteins, small and the large subunits?
    On which subunit are the mRNA binding, A, P, and E sites?
    Ribosomal RNA (rRNA) associates with a set of proteins to form ribosomes. These complex structures, which physically move along an mRNA molecule, catalyze the assembly of amino acids into protein chains.

    –Small subunit: matches tRNAs to codons

    • Large subunit; forms peptide
    • bonds (contains peptidyl transferase,
    • e.g. of ribozyme.

    -mRNA binding sites are on the smaller subunit
  8. Describe the structure and role of tRNAs. On
    which end (5’ or 3’) of the molecules is the amino acid attachment site?
    • •tRNA are
    • the “translators”
    • –Amino acid attachment site
    • –Anticodon (bp with
    • codon)
    • –Each tRNA binds to 1 specific aa
    • Its on the 3'
  9. To how many different types of amino acids can
    each unique tRNA molecule attach?
    –Each tRNA binds to 1 specific aa.
  10. Can each unique tRNA molecule base pair with
    more than one codon?
    • –>
    • 1 tRNA -
    • same a.a.

    • –Some tRNAs can
    • recognize > 1 codon (1st base
    • of anticodon can
    • form non-Watson-Crick pairs with 3rd base
    • of codon;
    • wobble base pairing)
  11. Contrast the number of tRNAs to that of amino acids and codons.
    –20 amino acids and 61 meaningful codons, but 31 or so tRNAs
  12. What is the function of aminoacyl synthetase?
    • Amino acid activation by aminoacyl-tRNA synthetase
    • Aminoacyl-tRNA synthetases couple a.a. to its tRNA (charged tRNA)
    • 1 synthetase for each a.a.
    • Some synthetases recognize >1 tRNA
  13. How many aminoacyl synthetases are there in most cells?
    20
  14. Can a aminoacyl synthetase recognize more than 1 tRNA?
    yes
  15. What is a charged tRNA?
    when a tRNA contains a animoacid
  16. How do a codon and its anticodon interact?
    –1st base of anticodon can form non-Watson-Crick pairs with 3rd base of codon; wobble base pairing)
  17. Be able to give the sequence of an anticodon if a codon sequence is given and vice
    versa.
  18. Explain wobble base-pairing. On which base of the codon and anticodon does it usually
    occur? What is special about the inosine base?
    • –Some tRNAs can
    • recognize > 1 codon (1st base
    • of anticodon can
    • form non-Watson-Crick pairs with 3rd base
    • of codon;
    • wobble base pairing)
    • Iosine base is created from the 3 bases  U,C,A
  19. Compare and contrast the bacterial and mature eukaryotic
    mRNA. What are UTRs?


    UTRs- untranslated RNA- on the outer part of start codon and stop codon.
  20. What is a ribosome binding site (what is it also
    known as)? Which one can be polycistronic?
    Shine-Delgarno sequence

    • Bacterial mRNAs can
    • be polycistronic or encode several different polypeptides (usually with
    • related functions) within the same transcript.
    • Bacterial mRNAs can
    • be polycistronic or encode several different polypeptides (usually with
    • related functions) within the same transcript.
    • Polycistronic transcription units are called operons.
  21. What does polycistronic mean?
    • Polycistronic transcription units
    • are called operons.

    • encode
    • several different polypeptides (usually with related functions) within the same
    • transcript.
  22. How do eukaryotes and bacteria differ in how to select for where to start
    translation? To which subunit of the ribosome do initiator tRNAfMet
    or tRNAMet, initiation factors, and mRNA bind? On which site (A, P,
    or E) does the initiator tRNA(f)Met bind? When does the other
    subunit bind?
    • In euks, ribosome binds to the start codon.
    • For bacteria they bind to the ribosome binding site. Small subunit then large subunit attaches.
  23. What is the initiating amino acid in bacteria?
    N-formylmethionine (fMet) – the initiating a.a. in bacteria
  24. know the level of details describedin Figs 22-10 and 22-11 but you don’t need to memorize the specific types of elongation factors.
  25. Outline the process of translation elongation and termination. What is happening at A,
    P, and E sites of the ribosomes?


    • P site hold the growing polypeptide.
    • A site hold the next animo acid being attached
    • E site detaches the tRNA
  26. Which catalytic molecule in the large subunit of a ribosome is an example of a
    ribozyme? What is its function?
    know the level of details describedin Figs 22-10 and 22-11 but you don’t need to memorize the specific types ofelongation factors.
  27. What occurs after a polypeptide is made?
    • Many proteins will fold
    • correctly during synthesis based on the amino acid sequence and interactions
    • with the cytoplasm
  28. Do all polypeptides require chaperone proteins
    for proper folding?
    no
  29. What roles do chaperone proteins play?
    • •Molecular chaperones can
    • assist proteins in correct folding or even help in the refolding of incorrectly
    • folded proteins

    •Unsaveable proteins are tagged for destruction

    • •Found in all three domains
    • of life and often designated as “Heat shock proteins”
  30. In which ways is a polypeptide processed?
    • •Chemical modification of amino acids (methylation, phosphorylation, acteylation)
    • • Proteolytic cleavage
    • • Protein splicing
  31. What is a polyribosome? What does its presence show? Does it occur in bacteria,
    eukaryotes, or both?
    • Polyribosomes (or polysomes): many ribosomes can translate the same mRNA molecule simultaneously.
    • occurs in bacteria
  32. How do polypeptides made by ribosomes attached to ER membranes vs. free ribosome
    differ in their destination?
    polypeptides made by ribosomes that are attached to the ER are transport to other membrane systems or exported out. Cotranslational import

    Polypeptides made by free ribosomes are other organelles. Post translation.
  33. Know the various types of mutations shown in Fig. 22B-1. Read box 22B in your
    textbook.
  34. Given
    a single-stranded DNA sequence, be able to

    -give
    the complementary sequence and

    -transcribe it using the template strand and give the mRNA sequence and

    -translate the mRNA into a peptide sequence.

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