Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The Three-Domain System was proposed by Carl Woese in , which divides all cellular life forms into three distinct domains based on the differences in the nucleotide sequences of .
Domain Archaea: Consists of prokaryotic organisms that lack peptidoglycan in their cell walls. Their membrane lipids are unique, composed of branched hydrocarbon chains attached to glycerol by ether linkages (), allowing them to survive in extreme environments.
Domain Bacteria: Includes true bacteria (eubacteria) with cell walls containing peptidoglycan. Their membrane lipids consist of unbranched fatty acid chains linked to glycerol by ester linkages ().
Domain Eukarya: Comprises all organisms with eukaryotic cells containing a membrane-bound nucleus and organelles. This domain is subdivided into four kingdoms: Protista, Fungi, Plantae, and Animalia.
The classification is based on the Svedberg unit () of ribosomal subunits, specifically focusing on the subunit of the prokaryotic ribosome and the subunit of the eukaryotic ribosome.
Molecular Phylogeny: This system emphasizes that Archaea and Eukarya share a more recent common ancestor with each other than either does with Bacteria, despite Archaea being prokaryotic in structure.
📐Formulae
💡Examples
Problem 1:
Identify the domain and specific characteristics of a methanogenic organism found in the gut of ruminants.
Solution:
Domain: Archaea.
Explanation:
Methanogens belong to the Domain Archaea. They are characterized by their ability to produce (methane) under anaerobic conditions and possess cell membranes with branched ether-linked lipids that lack peptidoglycan.
Problem 2:
Distinguish between the ribosomal RNA found in the small subunits of prokaryotic and eukaryotic ribosomes used for this classification.
Solution:
Prokaryotes (Bacteria and Archaea) use , while Eukaryotes use .
Explanation:
In the small subunit of prokaryotic ribosomes, the molecule is used for phylogenetic comparison. In the small subunit of eukaryotic ribosomes, the corresponding molecule is .