Penicillin kills many bacteria by blocking cell wall synthesis but has no effect on archaea. Why?
AArchaea have no ribosomes
BArchaeal cell walls lack peptidoglycan, the target of penicillin
CArchaea have a nucleus that protects them
DArchaea live only at temperatures where penicillin breaks down
Penicillin blocks the enzymes that cross-link peptidoglycan. Archaeal cell walls are built from other materials, such as protein surface layers (S-layers) or pseudopeptidoglycan, so the drug has no target.
Question 2 True / False
Archaea are found only in extreme environments such as hot springs and salt lakes.
TTrue
FFalse
Answer: False
Many of the first archaea studied were extremophiles, which created this impression. DNA surveys later found archaea in great numbers in ordinary seawater, soils and sediments, where some groups play major roles in nitrogen and carbon cycling.
Question 3 Short Answer
How do the membrane lipids of archaea differ from those of bacteria and eukaryotes?
Think about your answer, then reveal below.
Model answer: Archaeal lipids have branched isoprenoid chains joined to glycerol by ether bonds, while bacterial and eukaryotic lipids have unbranched fatty acid chains joined by ester bonds. Some archaea have lipids that span the whole membrane, forming a monolayer.
Ether bonds are more chemically stable than ester bonds, and membrane-spanning lipids resist coming apart. These features help some archaea survive extreme heat and acidity.
Question 4 Multiple Choice
In which feature are archaea more similar to eukaryotes than to bacteria?
APresence of a nucleus
BStructure of RNA polymerase and transcription factors such as TATA-binding protein
CPeptidoglycan cell walls
DMembrane-bound mitochondria
Archaeal RNA polymerase has many subunits and resembles eukaryotic RNA polymerase II, and archaea use transcription factors related to eukaryotic ones. Like bacteria, though, they lack a nucleus and mitochondria.