Proteins didn't have to come first
- The idea
- Predict
- See it
- Why
- Check
The idea
“Only proteins can catalyze reactions, so proteins had to come before RNA.”
Almost every enzyme you've studied is a protein. RNA can catalyze reactions too.
The short version
The mistake: Only proteins can catalyze reactions, so proteins had to come before RNA.
What's actually true: RNA can catalyze reactions and membranes form on their own, so early life didn't need protein enzymes.
- An enzyme lowers activation energy, partly by holding reactants in a folded active site. RNA can fold into one too. That's a ribozyme.
- In every ribosome today, the ribosomal RNA catalyzes each peptide bond. The ribosomal proteins don't.
- Fatty acids in water can form vesicles on their own. The first compartments may have formed that way.
- Proteins are built from instructions in nucleic acid. RNA can store information and catalyze reactions, so it could have come first. That's the RNA world hypothesis.
On the exam: RNA can fold into an active site and act as an enzyme, so RNA could have come first.