Features Of The Genetic Code Flashcards
What are the 3 key features of the genetic code ?
- degenerate
- universal
- non-overlapping
What is a start codon ?
The 3 bases at the start of a gene on DNA so it is copied onto mRNA as well
It (AUG) codes for methionine but it is later removed as it is not needed for the structure
It initiates translation
What is a stop codon
The final 3 bases at the end of the generic code that do not code for an amino acid
These mark the end of the polypeptide chain and cause ribosomes to detach and therefore stop translation as it does not have a complimentary anticodon with a particular amino acid
How many amino acids does the genetic code have to be able to code for ?
20
What is meant by the term degenerate ?
More than 1 triplet code, codes for the same amino acid as three are only 20 amino acids that can be made but 64 possible combinations with 4 bases
How can degenerate be proven mathematically ?
4^n
4 = number of bases
n = how long the base sequence is
So:
4^3 = 64 unique possibilities
Why is the DNA being degenerate an advantage ?
Because If a point mutation occurs, even if the triplet of bases is different, it may still code for the same amino acid and so it would have no effect
What is meant by the genetic code being universal ?
The same triplet of bases codes for the same amino acid in all organisms, so the genetic code is universal in all living organisms
Why is the genetic code being universal an advantage ?
Because it means genetic engineering is possible
E.g inserting human gene for insulin into bacteria
What is meant by the genetic code being non-overlapping ?
Each triplet code is unique from each other
So each base is only part of 1 triplet code
- so each codon or triplet of bases is read as a discrete unit
What is the advantage of the genetic code being non- overlapping ?
If a point mutation occurs, it will only affect 1 codon and therefore only 1 amino acid is affected
What are introns ?
Sections of DNA that do not code for amino acids and therefore polypeptide chains
Where are introns found ?
Introns are found in eukaryotic DNA but not in prokaryotic DNA
What happens to introns ?
Introns get spliced out of the mRNA molecules
What are exons ?
Sections of DNA that code for an amino acid
