4.1.6 The Triplet Code Flashcards
A gene is
a sequence of nucleotide bases in a DNA molecule that codes for the production of a specific sequence of amino acids, that in turn make up a specific polypeptide (protein)
The DNA nucleotide base code found within a gene is
a three-letter, or triplet, code
Each sequence of three bases (in other words each triplet of bases) codes for
one amino acid
These triplets of bases are known as
codons (each codon codes for a different amino acid – there are 20 different amino acids that cells use to make up different proteins)
A codon is
A sequence of three consecutive nucleotides in a DNA or RNA molecule that codes for a specific amino acid
CAG codes for the amino acid
valine
TTC codes for the amino acid
lysine
GAC codes for the amino acid
leucine
CCG codes for the amino acid
glycine
Some of these triplets of bases code for
start and stop signals
Code for start
TAC – methionine
Start and stop signals ensures
the cell reads the DNA correctly (the code is non-overlapping) and can produce the correct sequences of amino acids (and therefore the correct protein molecules) that it requires to function properly
There are four bases so there are
64 different triplets possible (4^3)
There are four bases so there are 64 different triplets possible (43), yet there are only 20 amino acids that commonly occur in biological proteins, this results in
multiple codons coding for the same amino acids
If multiple codons coding for the same amino acids the code is said to be
degenerate (this can limit the effect of mutations)
A DNA molecule with the triplet code for the codons of the start amino acid (methionine) and valine
