What Is LUCA?
Definition
LUCA (Last Universal Common Ancestor)
The last universal common ancestor of all present-day organisms, representing the root of the tree of life.
- LUCA likely lived around 4 billion years ago.
- Its existence is inferred from universal features shared across all life forms today.
Evidence For LUCA: The Genetic Code
Definition
Genetic code
The genetic code is a system that translates DNA instructions into proteins, the essential building blocks of life.
- One of the strongest pieces of evidence for LUCA is the near-universality of the genetic code across all organisms.
- The genetic code is a system that translates DNA sequences into proteins, essential for life.DNA is composed of four nucleotide bases: adenine (A), thymine (T), cytosine (C), and guanine (G).
- These bases are read in groups of three, called codons.
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 and also serves as a start signal for protein assembly.
Why Is the Genetic Code Universal?
- The genetic code is remarkably consistent across almost all organisms.
- Even vastly different organisms (humans and E. coli) use the same ribosomes to translate genetic instructions.
- The codon UUU codes for the amino acid phenylalanine in humans, yeast, and even bacteria.
- This shared "language" strongly suggests that all life on Earth shares a common origin.
What This Tells Us About LUCA
- If life arose independently multiple times, we would expect different genetic codes, like different human languages.
- Instead, the shared genetic code points to a single ancestral organism (LUCA) that passed it down to all descendants.
- Why is the genetic code considered universal, and what does this imply about the origins of life?
- What evidence supports the existence of LUCA, and what do we know about its environment?
- How might natural selection and environmental factors have led to the extinction of other life forms on early Earth?
