Chp 15.docx

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University of Toronto Scarborough
Biological Sciences

Growth Development and Cell Walls chapter 15y Development Overview1 Morphogenesis characteristics of tissuesorgans like specific forms regulation of plane of cell divisionrate direction of cell division etc 2 Differentiation change in gene expression causing biochemicalstructural changes that have specific functions ex cell wall vs plasmodesmata from pits 3 Intercellular communication coordinates development with other cells 4 Capacity to respond to the environment coordinating development with the environment Requires the detection of the environment and the use of signals plant hormones y Cell Wall OverviewStructural Components major sink of C 1 Rigid crystalline fibre cellulose microfibrils 2 Flexible epoxy matrix wall filler material made of 1 2 groups of polysaccharides hemicellulosespectin2 structural proteins From the first 2 you can the importance of polysaccrides nd3 Lignin a phenol polymer in a nonrandom arrangement that make the 2 wall solidsTable 151 CLASS EXAMPLES Cellulose Microfibrils of 14Bglucan Matrix polysaccharides1Pectins HomogalactoronanRhamnogalacturonan ArabinanGalactanXyloglucn 2 Hemicelluloses Xylan Glucomanan Arbinoxylan Callose Lignin Phenolic polymer Structural proteinsy Polysaccharides are made of monomers their name depends on the monomers names Primary Cell Wall cellulosematrix y 25 cellulosematrix 35 pectin 25 hemicelluloses25 protein y Cellulose microfibrils are synthesized on plasma membrane y Cellulose microfibrils aka rigid crystalline fibre y microfibrilschains of 14 BDglucose are tightly packed y microfibrils have variable length 200020000 glucose and variable thickness 2040 glucose chains y microfibrils Hbond with each othera form of association y microfibrils are resistant to physical tensile strength being pulled longitudinally comparable to steelchemicalenzymatic stress y the crystalline core is highly organized by Hbonding the surface glucoses are less orderedCellulose synthesis Particle Rosettes or terminal complexes on PM are large proteins made of 6 rosettes each rosette is made of 6 cellulose synthase CesA subunits Together 36 CesA form 36 glucanglucose chains which weave together to form a microfibrilCesA breaks sucrose into glucosefructorseuses the glucose to convert UDPUDPGtakes UDPG to apoplastic side and puts its glucose into a glucan chaintakes UDP back to the symplast side to pick up another GMicrotubules of symplast below cytoplasm are associated to microfibrils of apoplast above PM y Matrix components aka flexible epoxy matrix components are made in golgi then excreted and assembled in the cell wall space dynamic for cell growth
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