13.2: The Genetic Code

genetic code

informational key in which a sequence of mRNA nucleotides corresponding to a gene is translated into sequence of amino acids composing protein expressed by gene

codon

triplet code - sequence of 3 nucleotides in mRNA that specifies a single amino acid in protein

why is genetic code redundant but not ambiguous

Bc multiple codons code for the same amino acid = variations in mRNA sequence without affecting protein results - not ambiguous because each codon uniquely specifies only one amino acid, ensuring precise translation.

start codon

A specific codon that signals the beginning of translation, typically AUG, which codes for methionine.

stop codon

a codon that signals the termination of protein synthesis during translation.

structure of tRNA

Di typical secondary structure with an anticodon that’s complementary to mRNA codon

• 3’ end - amino acids attach - each tRNA carries a specific amino acid that corresponds to anticodon = when attached tRNA is charged

• no tRNA corresponds to any stop codons

open reading frame

region of DNA sequence that corresponds to mRNA transcript that can be translated by ribosome into polypeptide chain

• begins with start codon and ends with stop codon

• 3 possible reading frames depending if read from 1st, 2nd or 3rd nucleotide

• typically only 1 reading frame encodes functional protein