___________________________________ D. Fundamentals of Cell Movement What cell types move? ___________________________________ • Prokaryotes must find food, evade toxins • Free‐living ciliar and flagellar eukaryotes ___________________________________ • Plants don’t have motile cells but can demonstrate both rapid and slow movements due to cell activity • Animals have both ciliar and flagellar cells ___________________________________ • We also have cells that crawl, rather than swim Many cells during development and growth White blood cells responding to infection Wound healing cells ___________________________________ • Muscular movements in animals result from individual cell movements ___________________________________ ___________________________________ ___________________________________ What strategies do cells employ to move? ___________________________________ • Swimming through liquids: oars and propellers • Crawling on solid surfaces: grab‐pull‐release ___________________________________ • Selectively contracting some cells but not others: some use motor proteins, others water volume ___________________________________ • Even ‐ growing more cells, or letting some die, to move the entire structure closer or farther away! ___________________________________ ___________________________________ ___________________________________ ___________________________________ Many prokaryotic cells have a structure composed of a membrane‐bound motor complex driving propeller‐ ___________________________________ like movement of the extracellular flagellum ___________________________________ ___________________________________ The flagellum is composed ___________________________________ of the helical protein flagellin ___________________________________ Figure 1-18a Molecular Biology of the Cell, Fifth Edition (© Garland Science 2008) ___________________________________ The helical structure of flagellin allows for two kinds of ___________________________________ movement: coordinated linear vs. stationary ‘tumbling’ ___________________________________ RECEPTOR CHEMOTAXIS senses correct direction: will swim in a straight line for a ___________________________________ longer time before tumbling senses wrong direction: will tumble sooner and try a new direction at random. ___________________________________ finds the location with the highest concentration of an attractant (lowest of repellent ) ___________________________________ Even at high concentrations, can distinguish very small differences in concentration. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Two levels of regulation: 1. Signal transductio to motor ___________________________________ 2. Control of receptor activation ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 15-73 Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ Ciliar and Flagellar Eukaryotes ___________________________________ • The Basic Mechanism – Complex microtubular structures extend out from ___________________________________ the cell body under the plasma membrane – They extend out from basal bodies rather than centrisomes ___________________________________ – Immobilized dynein pulls retrograde and bends the microtubule ___________________________________ – Relaxation or a counter pull creates waving ___________________________________ ___________________________________ Free‐living eukaryote Didiniumhas two fringes of cilium used for swimming ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Here it is phagocytosing another eukaryotic cell as prey ___________________________________ Figure 1-32 Molecular Biology of the Cell, Fifth Edition (© Garland Science 2008) ___________________________________ Airway Epithelium ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ‐ G.I. epithelium ‐ Fallopian tubes ‐ Epidydimus ___________________________________ ___________________________________ ___________________________________ Flagellar Animal Cells ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ The structure of microtubules in both cilia and flagella are the classic 9+2: ___________________________________ An external ring of 9 doublets around 2 full microtubules ___________________________________ ___________________________________ ___________________________________ Figure 16-81a Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ ___________________________________ ___________________________________ Basal body structure is a ring of nine (9) triplets ___________________________________ Microtubules are nucleated from γ‐tubulin ___________________________________ and are capped and stabilized long‐term. Same as the centriole ___________________________________ Figure 16-84a Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ They work as a unit by being held together with ‘radial spoke’ and ‘nexin’ proteins. As dyneins attached to one doublet attempt to walk on the adjacent one they all bend. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 16-81b Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 16-83b Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ Mechanisms of Waving ___________________________________ • In long flagellum, sequential peristaltic contractions cause a whip‐ ___________________________________ like back and forth motion ___________________________________ • In short cilia, alternating side‐to‐side contractions or simple relaxations ___________________________________ cause waving ___________________________________ ___________________________________ Cell Migration or “Crawling” ___________________________________ • The Basic Mechanism ___________________________________ – Triggered by signals from outside the cell – Actin‐myosin based movement – Requires attachments to outside to pull against ___________________________________ – Gotta’ drag all of the cell contents along for the ride ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ In embryo development and ___________________________________ wound healing, epithelial cells can migrate as sheets. In general, these types of migrations are combinations ___________________________________ of cell division and directed migration. ___________________________________ ___________________________________ ___________________________________ Figure 16-20 Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ Chemotaxis ___________________________________ Circumferential receptors ___________________________________ Rho‐family GTPases (monomeric) Rho‐dependent kinases ___________________________________ 1. Actin monomer nucleotide exchange 2. Actin fiber polymerization and disassembly ___________________________________ 3. Myosin motor ATPase activity ___________________________________ ___________________________________ Cell type‐specific migration receptor ___________________________________ Rho family monomeric GTPase Rho‐dependent kinase ___________________________________ ___________________________________ Cell capable of migration ___________________________________ ___________________________________ Circumferential distribution of migration‐inducing signaling cascades ___________________________________ ___________________________________ Source of signal ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Leading edge extension is driven by actin polymerization. Cell membrane is physically pushed forward by actin 1. Core of all structures is very dense actin network ___________________________________ 2. Completely exclude membrane enclosed organelles. Leading edge contains everything needed