Codon

The genetic code is the basis for all life on Earth. Sequences of three nucleotides align each to an amino acid, and by reading this code ribosomes are able to stack amino acids sequentially into peptides, which can in turn fold into proteins.

1st base	2nd base								3rd base
	T		C		A		G
T	TTT	Phenylalanine	TCT	Serine	TAT	Tyrosine	TGT	Cysteine	T
	TTC		TCC		TAC		TGC		C
	TTA	Leucine	TCA		TAA	[STOP] Ochre	TGA	[STOP] Opal	A
	TTG		TCG		TAG	[STOP] Amber	TGG	Tryptophan	G
C	CTT		CCT	Proline	CAT	Histidine	CGT	Arginine	T
	CTC		CCC		CAC		CGC		C
	CTA		CCA		CAA	Glutamine	CGA		A
	CTG		CCG		CAG		CGG		G
A	ATT	Isoleucine	ACT	Threonine	AAT	Asparagine	AGT	Serine	T
	ATC		ACC		AAC		AGC		C
	ATA		ACA		AAA	Lysine	AGA	Arginine	A
	ATG	Methionine	ACG		AAG		AGG		G
G	GTT	Valine	GCT	Alanine	GAT	Aspartic acid	GGT	Glycine	T
	GTC		GCC		GAC		GGC		C
	GTA		GCA		GAA	Glutamic Acid	GGA		A
	GTG		GCG		GAG		GGG		G

DNA doesn’t directly turn into amino acids, however. First it basepairs with other nucleotides to generate a tRNA molecule in a process known as transcription. This is then translated into messenger RNA or mRNA (eukaryotic cells add an extra step to this by having a preliminary RNA strand coded with fidelity to the original DNA code, which then has introns snipped from it to produce a streamlined “mature” RNA strand). The mRNA is then read by the ribosome, which releases amino acids in a sequence prescribed by the mRNA, and ultimately, the DNA.

Figure 1 — Complex eukaryotic transcription & translation (left) versus streamlined bacterial transcription & translation (right). While bacterial transcription & translation can’t be truly described as simpler in any absolute sense (for they have more functions going on simultaneously at any given time and are in that way doubly complex as compared to eukaryotes), the process is definitely much-streamlined and has completely done away with complex steps.

1st base	2nd base								3rd base
	U		C		A		G
U	UUU	Phenylalanine	UCU	Serine	UAU	Tyrosine	UGU	Cysteine	U
	UUC		UCC		UAC		UGC		C
	UUA	Leucine	UCA		UAA	[STOP] Ochre	UGA	[STOP] Opal	A
	UUG		UCG		UAG	[STOP] Amber	UGG	Tryptophan	G
C	CUU		CCU	Proline	CAU	Histidine	CGU	Arginine	U
	CUC		CCC		CAC		CGC		C
	CUA		CCA		CAA	Glutamine	CGA		A
	CUG		CCG		CAG		CGG		G
A	AUU	Isoleucine	ACU	Threonine	AAU	Asparagine	AGU	Serine	U
	AUC		ACC		AAC		AGC		C
	AUA		ACA		AAA	Lysine	AGA	Arginine	A
	AUG	Methionine	ACG		AAG		AGG		G
G	GUU	Valine	GCU	Alanine	GAU	Aspartic acid	GGU	Glycine	U
	GUC		GCC		GAC		GGC		C
	GUA		GCA		GAA	Glutamic Acid	GGA		A
	GUG		GCG		GAG		GGG		G