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Bio251 Week 1.docx

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University of Toronto St. George
Rowan Sage

Bio251 Week 1 - Primary cell wall - Cell wall- unique to plants - In a mature plant very rigid, and acts as a skeleton for structure to be maintained, allows for hydrostatic pressure within the cell maintains the cell from a lot of pressure (turgor pressure provides structural support for physiological active cells) - Primary cell wall and secondary cell wall - Primary growth and secondary growth - Primary growth gives rise to an increase of the height of the plant opposed to lateral (trees) - Primary cell wall first cell wall that gets laid down, composed of many components MOST DOMINANT IS CELLULOSE , THEN HEMICELLULOSE AND SO ON - Hemicellulose forms a matrix linking cellulose fibres - Pectins gelatin like substance, binds a lot of calcium - Middle Lamella- symmetrical - Structural proteins - Non-structural proteins mostly enzymes - Synthesis of Cellulose Micro fibrils: - Cell wall is outside of the plasma membrane, and within the plasma membrane enzyme called cellulose synthase(Rosette) expands across plasma membrane…takes UDP glucose molecules and hooking them together to form long chains of glucose residues - Cellulose fibers-has hydrogen bonds between chains, forms very tight associations with one another - About 40 glucose chains to make a micelle (very stable) make up a cellulose micro fibril then those micro fibrils make a macro fibril bulky parts of the primary cell wall - Primary cell wall: - Laid down as cells are dividing - Region between cells middle lamella made of pectin, and loaded with calcium acts as a cement to keep cells together - Regions of continuity between one cell and the other cells, they are structurally and functionally interrelated by the plasmodesmata ( channels connecting cells together, incredibly small) in primary pit-field - Secondary cell walls: - Every plant cell has primary cell wall - Not every plant cell has a secondary cell wall - Secondary cell wall is adjacent to the plasma membrane, and the primary cell wall will be displaced when synthesized - Has three components; - S3 layer, s2 layer, s1 layer - In the secondary wall cellulose micro fibrils are laid down in very specific ways in each layer - Secondary walls have cellulose and LIGNIN HUGE molecule, incredibly hydrophobic molecule - Lack of pectin (incredibly hydrophobic molecules, keeps cell wall hydrated) - Water conducting cells with secondary cell walls has LIGNIN minimal resistance of H20 - Secondary wall doesn’t form a complete sheet, there is always gaps called pits - The pit  pit membrane is the one that has middle lamella and the primary wall ( not really a membrane, no secondary wall) - The Consequences of cell walls: - Restrict mobility, mobility comes from growth - Plasmodesmata: - Cytoplasmic channels within cell walls, connecting two cells together transfer of particular materials enhance communication - Laid down when the cell divides and after cell divides huge impact on controlling communication - Organelles: - Bounded by two membranes - Plastids(chloroplast) and mitochondria - Plastids - Chloroplast: - Site of photosynthesis - Thylakoid is round, stack of pennies - Grana, thylakoid, stroma - Different types of photosynthetic processes (I.e Not all chloroplasts form grana) - Chlorop
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