Cell Walls- Regulating Plant Cell Shape Flashcards
What is Cellulose?
Most abundant organic molecule on Earth
Glucose polymer, highly ordered
Form a major component of both primary and secondary cell walls (microfibrils)
What are the two phases in the cell wall structure?
Phase 1: crystalline microfibrillar phase = very ordered
Phase 2: non-crystalline matrix = not very ordered
What is the noncrystalline matrix made up of?
Hemicellulose: group of polysaccharides, form rigid structure
Pectin: branched, negatively charged polysaccharidess which bind water and have gel like properties
What is the protein extensin in cell wall structure?
The extensibility of cells can be controlled by extensin cross linking
Cross linking of pectin and cellulose dehydrates cell wall, reduces extensibility and increases strength
What is involved in the co-synthesis and delivery in the primary cell wall?
- Cellulose microfibrils at plasma membrane
- Polysaccharides in Golgi apparatus transported into wall by vesicles
- Cell wall proteins from rough ER
- Vesicles fuse to the plasma membrane
How do the cellulose-producing resottes move?
Parallel to the cortical microtubules (tubules that are close to plasma membrane)
What are the three key ways the cell wall functions in regulating cell shape?
- Influences cell morphology
- Provides structural support
- Prevents excessive water uptake
How is cell morphology influenced by orientation of cellulose microfibrils?
a) Randomly oriented: cell will expand equally in all directions
b) Right angles to long axis: cell expands longitudinally along axis
How does the cell wall provide structural support?
Protoplast pushes against cell wall making cells become rigid = maintains plant structure
Water loss reduces protoplast volume hence wilting occurs as the protoplast do not press on cell wall
How does the cell wall prevent excessive water uptake?
Water enters cell by osmosis and protoplast expands pushing against cell wall, pressure from cell wall limits volume of water that can be taken up
Vacuoles are important in this process as they contain water and make up a large portion of protoplast
How do vacuoles regulate cell shape?
High concentration of solutes in vacuole resulting in water uptake via osmosis. Plant cell limits water uptake = prevents cell from bursting. Plant cells build up a large internal pressure that contributes to plant structural support
What is the secondary cell wall?
Produced after cell growth has stopped (not all plants have), thicker and stronger than primary, provides more support than primary
Structure of secondary cell wall
Made up of multiple layers. Microfibrils in each layer have different orientations. Chemically: more cellulose, less pectin, lignin
What is lignin?
Complex polymer that has strength, rigidity and acts to exclude water, second most abundant organic macromolecule
What are plasmodesmatas?
Plasmodesmata are intercellular connections that enable cell to cell communication. Small enough to prevent organelle movements. Allows free exchange of small molecules
