The Genetic Code Is Universal
- The same codons (three-base sequences) specify the same amino acids in almost all organisms.
- There are only a few rare exceptions (e.g., some mitochondrial codons differ slightly), but these do not change the overall principle.
Definition
Codon
A codon is a sequence of three nucleotides in DNA or RNA that specifies a particular amino acid or a start/stop signal during protein synthesis.
The codon AUG codes for methionine in bacteria, plants, and animals alike.
TipExceptions (like in mitochondria or some protists) are rare and do not undermine the overall universality.
Implications of Universality
- Since the genetic code is the same, genetic information is transferable between species.
- A gene from one organism can be inserted into another, and the recipient will still produce the correct protein.
- This is why genetic engineering (e.g., inserting the human insulin gene into bacteria) is possible.
Consistency in Protein Synthesis
- All life forms use the same fundamental process, where DNA is transcribed into RNA, which is translated into proteins.
- This conserved mechanism highlights a common evolutionary blueprint.
The genetic code refers to how codons map to amino acids, not the specific genes or traits an organism has.
Shared Ancestry
- The near-universal genetic code suggests that all modern organisms descended from a single ancestral organism.
- Variations in the code are rare and found only in some specialized organisms, reinforcing the code's stability over billions of years.
- IB students are not required to memorize specific codons or exceptions.
- Only that the genetic code is universal.
Coding and Non-Coding Sequences
- A genome includes both coding sequences (genes that produce proteins) and non-coding sequences (regulatory or structural DNA that does not code for proteins).
- Some sequences have remained unchanged across species, known as conserved sequences.
- Highly conserved sequences are often found in:
- Genes for transcription and translation (e.g., rRNA genes).
- Genes for histone proteins, which package DNA in the nucleus.
- What does it mean that the genetic code is universal?
- How does the universality of the genetic code make genetic engineering possible?
- What is a conserved sequence, and why are such sequences important?
