Module 4 Section 3 Flashcards

1
Q

Three important characteristics of the genetic code

A
  1. Degenerate
    - 64 unique ways to combine 4 different nucleotides in triplet sequence, but only 20 common AA
    - multiple codons encode the same AA
  2. Robust
    - can absorb single nucleotide mutations with minimal consequences to the protein it encodes
    - due to degeneracy
  3. Universal
    - All life on earth uses this genetic code
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2
Q

Rules of the genetic code (5)

A
  1. non-overlapping
  2. does not contain pauses
  3. code is read in triplets
  4. it is read in a linear fashion
  5. The code is resistant to mutations
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3
Q

The reading frame

A
  • Need a Met followed by a long stretch of w/o a stop codon
  • if nucleotides randomly distributed, STOP codon would appear every 3/64 (~20) codons
  • specific sequences in the mRNA also signal the start of translation
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4
Q

Pauses in genetic code

A
  • does NOT happen
  • would make the reading frame immune to frameshift mutations, insertions and deletions would only alter one AA
  • researchers used acridines (mutagens) to induce insertion/deletion mutations
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5
Q

Translation is linear

A
  • mRNA read 5’ to 3’ direction

- proteins synthesized from N-term to C-term

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6
Q

Transition mutation

A
  • most common mutation
  • purine is replaced with purine or pyrimidine replaced with pyrimidine
  • mutation in 3rd codon position rarely causes change
  • mutation in 2nd codon tend to conserve chemical structure
  • mutation in 1st position for most codons causes AA change, usually a chemically similar AA
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7
Q

Silent Mutation

A
  • no change in AA sequence

- non-deleterious

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8
Q

Missense Mutation

A
  • single-base substitution that leads to replacement of one AA with another
  • can be deleterious or non-deleterious
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9
Q

Nonsense Mutation

A
  • codon change that results in a termination codon
  • abort protein synthesis, resulting in an incomplete protein that is rarely functional
  • usually very deleterious
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10
Q

Non-Stop

A
  • Results in the loss of a stop codon
  • similar to nonsense, subject to degradation early in translation, no protein produced
  • deleterious
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