Alternative splicing and one gene, many proteins · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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One gene, many proteins

Science · Biochemistry & Molecular Biology · ages 20-21
Name ______________________   Date ____________

  1. Which RNA features guide spliceosome-mediated intron removal?

    • Translation start and stop codons beside a poly-A tail
    • Promoter elements and enhancer-binding motifs on DNA
    • Splice sites and a branch point adenosine

  2. During ordinary intron removal, which region does the spliceosome remove?

    • The adjacent exons
    • The intervening intron
    • The untranslated exons

  3. Skipping any cassette exon always removes one whole protein domain.

    Circle one:   True   False

  4. An RNA retains Start and End. Between them it must retain exactly one of exons X and Y. Both choices are allowed. How many RNA arrangements are possible?

    Answer: ______________

  5. Two distinct optional exons can each independently be kept or skipped. All combinations are allowed. How many RNA arrangements are possible?

    • Two arrangements
    • Four arrangements
    • Six arrangements

  6. An intronic variant disrupts a splice site without changing coding DNA. Which outcome is possible?

    • A protein change only if a coding base is also substituted
    • Exon skipping or use of a cryptic splice site
    • Identical splicing because the exonic coding sequence is unchanged

  7. An intronic splice-site variant changes a protein. A student concludes it directly changed coding DNA. Which correction is supported?

    • The protein difference proves that the variant lies in an exon
    • An unchanged coding sequence rules out altered protein sequence
    • Altered RNA processing can change the protein

  8. An hnRNP represses site S when bound beside it. An experiment increases occupancy there, and site use falls as occupancy rises. Other relevant conditions stay fixed. What is predicted?

    • Less use of site S
    • More use of site S because occupancy promotes recognition
    • Unchanged use of site S because the RNA sequence is unchanged
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Answer key

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One gene, many proteins W1-mt_xei9v3IIsE-s1

  1. Splice sites and a branch point adenosine · The spliceosome uses the 5 prime and 3 prime splice sites together with a branch point adenosine.
  2. The intervening intron · The intron is removed and adjacent exons are joined. Untranslated sequence can remain within exons.
  3. False · Exons need not align with whole domains. Some contain untranslated sequence, and skipping can have other effects.
  4. 2 · The allowed arrangements are Start-X-End and Start-Y-End: two arrangements.
  5. Four arrangements · There are two choices for each exon: 2 times 2 = 4 arrangements.
  6. Exon skipping or use of a cryptic splice site · Splice-site disruption can alter RNA processing even without a direct coding-DNA change.
  7. Altered RNA processing can change the protein · This variant lies in an intron. Altered splicing can change mature RNA and its protein without directly changing coding DNA.
  8. Less use of site S · The experiment states both the local repressive effect and the response to greater occupancy, supporting reduced use of S.
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