The third domain of life

Science · Microbiology · ages 18-19

Name ______________________ Date ____________

What type of chain is usual in bacterial membrane lipids?
- Branched sugar chains
- Linked protein chains
- Fatty acid chains
Typical archaeal membrane lipids attach their chains to glycerol with which links?
- Ester links
- Ether links
- Peptide links
Comparisons of ribosomal RNA sequences support separating Archaea from Bacteria.
Circle one: True False
In the three-domain classification, which set names the domains?
- Bacteria, Protista and Animalia
- Bacteria, Archaea and Eukarya
- Archaea, Fungi and Plantae
Which statement explains a membrane feature that can help some archaea tolerate high temperatures?
- Every archaeon fuses two existing membrane layers when heated.
- All archaeal membranes become twice as thick as bacterial membranes.
- Membrane-spanning lipids can form a stable monolayer.
A newly studied microbe grows in acidic water. Does this observation alone identify it as an archaeon?
- Yes; every microbe found in acidic water belongs to Archaea.
- Yes; acidity identifies its domain if its cells are small.
- No; bacteria can tolerate acidic conditions too.
Which pair consists of archaeal groups?
- Methanogens and haloarchaea
- Cyanobacteria and soil bacteria
- Skin bacteria and gut bacteria
Which archaeal machinery has many components resembling those in eukaryotes?
- Membrane lipid synthesis alone
- Transcription and translation
- Cell-wall peptidoglycan synthesis

Answer key

For grown-ups. Fold this page away before handing over the rest.

Fatty acid chains · Bacterial membrane lipids usually contain fatty acid chains. Branched isoprenoid chains are characteristic of archaeal lipids.
Ether links · Ether links join the chains to glycerol in typical archaeal membrane lipids.
True · Ribosomal RNA sequence comparisons provide molecular evidence that distinguishes archaeal and bacterial lineages.
Bacteria, Archaea and Eukarya · The three-domain classification names Bacteria, Archaea and Eukarya.
Membrane-spanning lipids can form a stable monolayer. · Some archaeal lipids span the membrane, forming a monolayer that can aid stability at high temperatures. This feature is not universal.
No; bacteria can tolerate acidic conditions too. · Acid tolerance is not exclusive to Archaea. Molecular comparisons provide evidence for domain identification.
Methanogens and haloarchaea · Methanogens and haloarchaea are archaeal groups. Halophile is broader and also includes salt-loving bacteria.
Transcription and translation · Many archaeal components for transcription and translation resemble those of eukaryotes.