Lecture 8 Flashcards
What cell components are only found in plant cells?
- chloroplast
- central vacuole
- cell wall
- plasmodesmata
What is the structure of the cell wall?
- glucose polymer
- highly ordered
- long, ribbon-like
- indigestible to humans
- forms microfibrils
- very strong
What are the two cell wall structure phases and what are they comprised of?
Phase 1 - Microfibrils, Crystalline phase : Cellulose
Phase 2 - Matrix, non-crystalline matrix : Pectin polysaccharides + hemicellulose polysaccharides
What is extensin?
It is a protein that is used to make the cell wall tougher by cross-linking and dehydrating, reducing extensibility.
What is hemicellulose and its purpose?
- polysaccharide w/side branches
- can lie next to microfibril and side chains will join w/other microfibril or hemicellulose
- makes the cell wall rigid
What is pectin and its purpose?
- polysaccharide (branched)
- gel-like
- can bind/hold water
Synthesis of the primary cell wall requires the co-ordinate synthesis and delivery of :
- Cellulose Microfibrils, synthesises at the plasma membrane, manufactured by enzymes in plasma membrane, takes glucose from the cytoplasm. It is synthesised outside of the cell.
- Polysaccharides (hemicellulose and pectin), synthesised in golgi and transported to plasma membrane with exocytosis
- Extensin, synthesised in rER and transported via golgi to plasma membrane with constitutive exocytosis
How is the primary cell wall synthesised?
- cellulose is produced by rosette (cellulose synthase) as raw materials come in
- forms microfibrils outside of the cell
- cortical microtubules run parallel to rosettes on inside of cell, which controls direction of synthesis of Microfibrils (parallel to microtubules)
- Microfibrils joined together with hemicullulose
- pectin in between, holding stuff together
- cells walls will be glued together with pectin with the middle lamella
What are the functions of the cell wall?
- regulating cell morphology. The orientation of microfibrils influences cell shape + growth. If randomly orientated the cell will expand equally in all directions. If they are laid parallel, the cell will expand in width but not length
- provides structural support. Protoplast pushes against the cell wall making the cell rigid and maintaining cell structure
- prevents excessive water uptake. The central vacuole is higher in solutes, so water is trying to enter cell via osmosis. This creates a high amount of pressure from the central vacuole called turgor pressure. The cell wall resists this pressure and is strong so won’t burst.
What is the function of the central vacuole?
The central vacuole is an organelle which takes up water due to its high solute content, providing structure to the cell.
What happens to a plant cell in a hypertonic, isotonic, and hypotonic solution?
Hypotonic = normal
Isotonic = flaccid
Hypertonic = plasmolyzed
What is the secondary plant wall? When is it produced? What is its purpose?
The secondary plant walls are additional cell walls for added structural support. They are thicker than the primary cell wall and occur in multiple layers. They are the innermost layers, and “push” away the primary cell wall. Each added layer also reorientates the microtubules to ensure that the microfibrils are in different orientations for added strength.
What is the structure of the secondary plant cell walls?
Made of:
- more cellulose than primary cell wall
- less pectin than primary cell wall
- lignin (replaces the less pectin)
What is lignin and what is its purpose? Where is it found?
Part of the secondary plant cell wall. It is found between cellulose. It is waterproof and tough, and gives strength and rigidity. It’s found in water transporting cells that don’t want to be broken down by water.
What is the plasmodesmata and how does it work?
They are ‘tunnels’ that form cytoplasmic connections between cells. These are intercellular connections for cell communication. They are small enough to prevent organelle movements, but allows the movement of small molecules.
