1Lec. 3. Plant cells: components and functions• To understand how plants behave, we need to focus on the units. What do plant cells do? • Outline: • Cells are dynamic units of life. Cells differ in their shape and function. All cells are derived from meristems. Thus all cells share basic structural and functional traits.• Structure: What are the subcellularparts? What do they look like?• Function: What are the major roles of each organelle?• Origin: where did each come from?• What are unique structures and functions? Plastid, vacuole, cell wall, cytoskeleton, plasmadesmataCells divide, elongate & differentiateAll cells are derived from meristems.Thus all cells share basic structural and functional traits.There is no “typical”Plant Cell.Leaf consists of many cell types1-4. Plant leaf cellAll cells originate from meristem cells. Meristem cell: one that can divide continuously.Differentiated cell –Leaf Mesophyll cellHow do the two cellsdiffer?2•Properties of membranes• p-lipids and proteins•Example-Plasma membrane•Regulate passage of ions and nutrients.•separate organelles from cytoplasm•Generate energy.Organelles that contain the information of lifeDouble membrane organelles•Nucleus•Mitochondria•Plastid•Have 2 membranes•Contain DNA and RNA•DNA synthesis and transcription•Nuc is unique to eukaryotes•Mitochondria and plastid originated from prokaryotes millions of years ago. •Mitochondrion and plastid divide by fission to form new organelles. How was a eukaryotic cell formed?PredatorSymbiosisOrigin of chloroplastOrigin of mitochondriaNucleusFunction?1. Control center of gene expression2. Store and duplicate genetic materialNuclear pore allows passage of small & large molecules,e.g. selected proteins and RNAA nuclear poreSite of ATP production. ??3Mitochondrion divide by fission• Show pic from KarpInside: pH 7.4100-200 mM K< 1 μMCa-100 mVOutside: pH ~5.5 (acidic)trace ions ~ 1 mM K, Ca, Naother ions < 1 mMFig. 1-7. E coli divide by fissionPlastid:chloroplastOther Plastids:chromoplastamyloplastPlastids differentiate as cells develop M Knee, OHIO St U.Endomembrane system-Synthesis and sorting of membrane and secreted proteinsERGolgiVacuoleSecretoryvesiclesPlasma membraneEndomembrane systemER- source of other membranes, -membrane proteins and -secreted proteins are made here-p-lipid synthesis Golgi- proteins are modified and sorted to destination synthesis of cell wall material in plants Vacuole- large and multifunctional in plants Plasma membrane-Very dynamic- membrane trafficking4Endoplasmic reticulum:source for other membranessite of synthesis--p-lipids-membrane proteins-secreted proteinsEMSmooth vs rough ?What does Golgi do? A. Proteins synthesized in the ER,-modified and -sorted in the Golgi,-soluble proteins are secreted at the PM or delivered to vacuole.B. Cell wall polysaccharides are synthesized, modified in the Golgi, and delivered to the cell wall.Proteins & wall materials are carried by vesicles. Vesicles bud, move, fuse.= Vesicular transport16-13. Shoot apical meristem cells are much smaller than other cells. Cell expansion is due to vacuole enlargementWhat is a vacuole? A single membrane organelle Vacuoles- unique organelle Small in meristem cells.Large in mature cells, up to 90% of cell volume.Functions: many1. Osmotically active compartment needed for cell expansionStore of ions, water, many molecules 2. Storage site of secondary products. Storage depot- sugar (sugar cane)3. Defense: nicotineAttractant: pigments in petals4. Recycling center: enzymesCytoplasm•Contains most metabolites, ions•Enzymes for biosynthesis and for breakdown.1. Sugar breakdown: glucose 6C --->2 ( 3C) sugar2. Synthesis of sugars, amino acids, lipid precursors3. Synthesis of proteins in cytoplasmsynthesis of mitochondrial and chloroplast proteins•An interconnected network of filamentous proteins keeps the contents in cytoplasm organized -cytoskeletonThe cytoskeleton(Farabee-5)-Determines cell shape-organizes cytoplasm-aids in transport of vesicles & chromosome-brings about motility5Actin and tubulin filaments of the cytoskeleton. Filaments can be assembled and disassembled.Dynamic states of Microtubules and Microfilaments before and during mitosis of plant cellsMT- yellow/greenChromosome- blueMitosis in Plant Cell1-251.29 Myosin-mediated transport of organelles along actin microfilaments6Living cells are dynamicCytokinesis movie (Nebenfuhr ) http://botany1.bio.utk.edu/cellbiol/iv/ck.htmGolgi & cytoskeletonCytoplasmic streamingCell plate formation (Wolniak)1-5. Taiz. What is the Plant cell wall? pectinFunctions:Cell shapeSupportProtectionConductanceCell adherenceMolecules can penetrateWater & ions flowGas can diffuse------------------------------------------------------------------------------------Wall: main components PrimarySecondary------------------------------------------------------------------------------------Polysaccharides 90% 65-85%Cellulose 30 50-80Hemicellulose 30 5-30Pectin 30 ---Proteins 10% ---Lignin 15-35------------------------------------------------------------------------------------Chemical components that make up the cell wall.Taiz: Table 15-1Cellulose : most abundant organic C compound in nature15-4. Model of cell wallCell Wall Model= Taiz 15-4 & 15-6Cellulose is a linear polymer of glucose units.Cellulose microfibril is a bundle of cellulose polymers.715-10. Hemicellulose: is branched and made of a complex mixture of sugars. E.g. Backbone is glucose. Branches are 5C sugars. 15-11 , 15-12Pectin is a mixture of polymers. E.g. Galacturonic acidBranched or linear15-12. Ca ions bridge carboxyl groups of GalA in pectin.Thus pectins act as a glue.Cellulose microfibrils-SEMHow is the primary wall formed?Pectins and hemicellulose are synthesized in the Golgi, and transported to the PM, and secreted to form the cell wall8Cellulose is made at the PMEach Cellulase synthase complex makes a microfibril.Each rosette subunit has 6 Ces, the complex has 36 Ces.Taiz 15-7. Cellulose is synthesized at the plasma membrane. Cellulose microfibrils align with microtubules.Taiz 15-17. Phenolic subunits fill in spaces and are cross-linkedLignin: 2nd most abundant organic cpd in natureHinders degradation of cell walls.Taiz 1-30. Plasmadesmataconnect cytoplasm of adjacent cells.Cell-cell communication via plasmadesmata91-27Review1. Novel organelles/part in plant cells ?Name 32. Where can you find dividing