雅思阅读 115: Can Life Run on Only 19 Amino Acids?

Adapted from 'Scientists use AI to test whether life can run on only 19 amino acids', Scientific American, April 2026.

🎧 课文朗读音频

Reading Passage

Nearly all known life builds proteins from the same alphabet of 20 canonical amino acids. Strung together in different orders, these building blocks form the proteins that make cells work. In a new Science study, researchers at Columbia, MIT and Harvard used AI-guided protein design to test how much of that alphabet can be pared back. They engineered an E. coli strain that survived after being redesigned to lack one specific amino acid, isoleucine, in its ribosomal proteins.

The team did not create a true 19-amino-acid organism; the engineered strain still uses isoleucine throughout most of its genome. But the result suggests that one of lifes most ancient machines can tolerate at least partial simplification, and that AI may help biologists test the limits of lifes chemistry.

Think about language, says senior author Harris Wang. There are 26 letters in English, but do you really need 26, or can you simplify to 25 or 24? The team chose isoleucine because it resembles valine and leucine closely enough that some proteins might tolerate its removal. They targeted ribosomes, the molecular machines that build proteins and consist of more than 50 proteins.

The first attempt was brute force: replacing every isoleucine with valine or leucine. The bacteria survived but poorly, at about 40 percent of wild-type fitness. The target was 90 percent. To close the gap, researchers turned to AI. They combined sequence-based protein language models such as ESM2 with structure-based models such as AlphaFold2 and ProteinMPNN to suggest mutations and verify the proteins folded correctly.

The AI designs were surprising. In one ribosomal protein, the AI remodeled an alpha helix and introduced eight new mutations to compensate for just two isoleucine substitutions. Maybe these machine-learning systems know aspects of biology we can verify but do not yet understand, Wang says.

The final strain, Ec19, carries 21 isoleucine-free ribosomal proteins and maintains fitness above 90 percent over 450 generations. A truly 19-amino-acid organism will require cheaper DNA synthesis and more capable AI models. But showing that the oldest molecular machine can survive partial simplification gives researchers a template for the rest of life.

Questions 1-5

Choose the correct letter, A, B, C or D.

1. How many canonical amino acids does life use? A. 19 B. 20 C. 21 D. 26
2. Which amino acid did the team remove? A. Valine B. Leucine C. Isoleucine D. Alanine
3. What organism was engineered? A. Yeast B. E. coli C. Human cells D. A mouse
4. What was the fitness after brute-force replacement? A. 90% B. 100% C. About 40% D. 10%
5. What does the final strain Ec19 achieve? A. It uses only 19 amino acids entirely B. It has 21 isoleucine-free ribosomal proteins and 90% fitness C. It is dead D. It grows faster than wild type

Questions 6-10

Do the following statements agree with the information? Write TRUE, FALSE or NOT GIVEN.

6. The engineered organism is a true 19-amino-acid life form.
7. Isoleucine is similar to valine and leucine.
8. AI models suggested mutations humans had not anticipated.
9. The strain reverted to wild type after 450 generations.
10. The study was published in Nature.

Questions 11-13

Complete the summary. Choose ONE WORD ONLY.

Researchers removed 1 from ribosomal proteins. Brute-force replacement gave only 40 percent 2. AI models suggested unexpected 3 that restored fitness to 90 percent.

Answers

1. B 2. C 3. B 4. C 5. B
2. FALSE 7. TRUE 8. TRUE 9. FALSE 10. FALSE
3. isoleucine 12. fitness 13. mutations

Key Vocabulary

⬅️ 上一篇 ｜ 📚 目录 ｜ 下一篇 ➡️