Module 4 Section 3 Flashcards
1
Q
Three important characteristics of the genetic code
A
- Degenerate
- 64 unique ways to combine 4 different nucleotides in triplet sequence, but only 20 common AA
- multiple codons encode the same AA - Robust
- can absorb single nucleotide mutations with minimal consequences to the protein it encodes
- due to degeneracy - Universal
- All life on earth uses this genetic code
2
Q
Rules of the genetic code (5)
A
- non-overlapping
- does not contain pauses
- code is read in triplets
- it is read in a linear fashion
- The code is resistant to mutations
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
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
5
Q
Translation is linear
A
- mRNA read 5’ to 3’ direction
- proteins synthesized from N-term to C-term
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
7
Q
Silent Mutation
A
- no change in AA sequence
- non-deleterious
8
Q
Missense Mutation
A
- single-base substitution that leads to replacement of one AA with another
- can be deleterious or non-deleterious
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
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