MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
A scientist is investigating a newly discovered bacterium that thrives in extremely hot, acidic environments. Analysis of its cellular components reveals specialized membrane lipids with hydrocarbon chains linked to glycerol by ether bonds, and a cell wall composed of pseudopeptidoglycan. Based on these characteristics, to which domain of life does this organism most likely belong?
- AFungi
- BBacteria
- CArchaea
- DEukarya
Show answer & explanationAnswer & explanation
Correct answer: C. Archaea
The presence of ether-linked membrane lipids and pseudopeptidoglycan in the cell wall are hallmark characteristics of Archaea, which are known for inhabiting extreme environments (extremophiles).
Why the other options are wrong
- A. Fungi are eukaryotes, having ester-linked lipids and chitin cell walls.
- B. Bacteria typically have ester-linked membrane lipids and cell walls made of peptidoglycan.
- D. Eukarya have ester-linked lipids and diverse cell wall compositions (e.g., cellulose in plants, chitin in fungi) or lack cell walls.
Characteristics of Archaea
Archaea are a domain of single-celled microorganisms that are prokaryotes, distinct from bacteria and eukaryotes, often thriving in extreme environments.
- Membrane lipids have ether linkages (not ester linkages like Bacteria/Eukarya).
- Cell walls may contain pseudopeptidoglycan or S-layers, but never peptidoglycan.
- Many are extremophiles (thermophiles, halophiles, acidophiles).
Memory trick: Remember 'BAE' for the three domains.