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#cell shape

3 public questions tagged with this topic.

Basics of Cell Biology

Which of the following is not a function of the cytoskeleton?

Cytoskeletal networks coordinate shape, division, and intracellular logistics. Actin filaments, 7 nm flexible helical polymers of ATP-G-actin nucleated by Arp2/3 at 70 degree branch and formins for linear cables, interact with 50 myosin classes for cortical contraction, formation of contractile ring with myosin II during cytokinesis, lamellipodial protrusion, and vesicle movement near periphery. Microtubules, 25 nm rigid hollow tubes of alpha-beta tubulin heterodimers assembling head to tail with GTP cap regulating dynamic instability, serve as polarized tracks for kinesin families moving outward to plus ends and dynein moving inward, positioning Golgi, endosomes, mitochondria, and assembling mitotic spindle with kinetochore capture ensuring chromosome segregation. Intermediate filaments, 10 nm non-polar rope-like polymers keratin, vimentin, desmin, lamins anchored via plectin and nesprin, provide mechanical resilience against shear stress. Together they govern intracellular transport, mechanical support, and motility. Protein synthesis uses ribosomal peptidyl transferase in cytoplasm and rough ER, not filaments, so translation is not cytoskeletal function.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Cytoskeleton Functions Overview.

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Microbial Physiology

The MreB cytoskeletal protein plays a role in:

MreB is a widely distributed bacterial homolog of eukaryotic actin conserved across rod-shaped bacteria including Escherichia coli, Bacillus subtilis, and Caulobacter crescentus, essential for maintaining cylindrical morphology and coordinating growth. Unlike eukaryotic actin that forms long helical filaments, MreB assembles into short, antiparallel double protofilaments associated with inner face of cytoplasmic membrane in an ATP-dependent manner, often guided by membrane regions enriched in specific phospholipids. Its primary morphogenetic function is to act as a dynamic scaffold organizing cell wall synthetic complexes, recruiting penicillin-binding protein PBP2, rod shape-determining proteins RodA and RodZ, and class A bifunctional transglycosylases, directing their processive circumferential motion around cell long axis tracked by single-molecule imaging. This coordinated movement ensures new peptidoglycan glycan strands are inserted in ordered hoops rather than randomly, preserving width and straightness during elongation. Pharmacological depolymerization with compound A22 or genetic depletion converts rods into spheres, reduces growth rate, and disorganizes wall insertion. FtsZ instead assembles Z-ring for division, illustrating division of labor between elongation and cytokinesis.

Ref: Burkman et al., Ann Rev Microbiol 2018, MreB and Rod Shape; Errington, Nature Rev Microbiol 2015, Bacterial Cytoskeleton.

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