#prokaryotes

Glycolipid and Phospholipid

Which lipid is absent in most prokaryotic and plant membranes?

Evolutionary lipidomics reveals sterol distribution discontinuous across domains life reflecting oxygen dependent biosynthesis pathway complexity. Eukaryotes animals synthesize cholesterol via HMGCoA reductase squalene monooxygenase epoxidase lanosterol fourteen demethylase CYP51 DHCR enzymes pathway requiring molecular oxygen maintaining thirty to forty percent plasma membrane buffering fluidity organizing rafts signaling. Fungi use ergosterol additional double bonds methyl group phytosterol plants stigmasterol sitosterol campesterol from cycloartenol SMT sterol methyltransferase modification

Ref: Nes WD, Chem Rev 2011, Sterol biosynthesis diversity bacterial absence cholesterol and hopanoids.

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Cytoskeleton

The actin cytoskeleton in prokaryotic cells is functionally similar to which of the following eukaryotic proteins?

Prokaryotic cells maintain rod shape and organize cell wall synthesis without eukaryotic compartments using cytoskeletal homologs sharing ancient ATPase fold. MreB, belonging to actin Hsp70 superfamily, shares structural core of five conserved sequence motifs forming ATP binding pocket between domains IA and IIA. Purified MreB polymerizes into ATP dependent antiparallel double filaments that rotate circumferentially beneath cytoplasmic membrane driven by cell wall elongation machinery. It scaffolds elongasome complex containing RodA glycosyltransferase, PBP2 transpeptidase and MreC MreD, direc

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Cytoskeleton and Bacterial Homologs MreB.

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Microbial Physiology

Which domain of life do Archaea belong to?

Archaea represent a distinct domain of life alongside Bacteria and Eukarya, established by Carl Woese through comparative analysis of 16S ribosomal RNA sequences. Morphologically they resemble bacteria as prokaryotes lacking membrane-bound nucleus, typically possessing circular chromosomes and 70S-like ribosomes, yet they exhibit unique molecular features in transcription, translation, and membrane composition that separate them from true bacteria. For educational simplification, archaea are often grouped under broad term prokaryotes to contrast with eukaryotes that contain nuclear envelope, l

Ref: Woese & Fox, PNAS 1977, Phylogenetic Structure of Prokaryotes; Madigan et al., Brock Biology, Archaea Domain.

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Microbial Physiology

The bacterial reproduction process of binary fission differs from mitosis in that:

Binary fission represents prokaryotic division program fundamentally distinct from eukaryotic mitosis in mechanism and regulation. Initiation begins with replication of single circular chromosome from unique origin oriC proceeding bidirectionally via replisomes containing DNA polymerase III. Segregation of origins is mediated by ParABS partitioning system and SMC condensin complexes moving DNA toward opposite poles as cell elongates via MreB-guided peptidoglycan insertion. Division site selection uses precise regulatory systems: oscillating MinCDE proteins concentrate MinC inhibitor at poles p

Ref: Madigan et al., Brock Biology of Microorganisms, 16th ed., Chapter 4: Binary Fission and Absence of Spindle Apparatus.

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Regulation of Gene Expression - Lac Operon

Which of the following correctly describes an inducible operon?

An inducible operon (such as the lac operon) is normally off but can be activated by an inducer like lactose.