Lecture 14 Flashcards
What are the main components that make up the cell wall and what is the substance in between the cell wall? (3)
Primary Wall
(Three layers of secondary wall)
Middle Lamella
What are the components that make up the primary cell wall? What are their percentages?
Cellulose 20-30%
Hemicellulose 15-25%
Pectin 35%
Protein 5-10%
What are the characteristics of the primary cell wall?
Produced by….
Relatively…
Cells are…
Produced by young cells
Relatively thin and flexible
Cells are still able to grow
What is the overall description of the primary cell wall composition?
Two phases plus a network of extensin
What are the two phases of the cell wall? What do each phase contain within?
- Crystalline phase
- Cellulose - Noncrystalline matrix
- Pectin
- Hemicellulose
What is the function of the extensins?
Extensin cross-link pectin and cellulose
Dehydrates the cell wall
Reduces extensibility and increases strength of the cell wall.
Steps of the Synthesis of primary cell wall .
- Microfibrils are laid down at the plasma membrane
- Pectin and Hemicellulose in the Golgi are transported to the cell wall in vesicles
- Extensins from the rough ER will fuse to the plasma membrane
Synthesis of Cellulose microfibrils and orientation.
There is the breakdown of sucrose into fructose and glucose in the complex.
Glucose is polymerised in the Rosette containing the enzyme cellulose synthase.
The cellulose microfibrils move parallel to the cortical microtubules.
The orientation of the microtubules then determine the orientation of the microfibrils that make up the cellulose.
What is cellulose made from?
Strands of microfibrils
Cell wall functions (3)
Structural Support and cell morphology
Protection
Controls turgor pressure, prevents excessive water uptake.
What are the different orientations of the microfibrils of the primary cell wall?
- Cell will expand in all directions
2. Cell wall will expand longitudinally along the long axis of cell wall.
What are the characteristics of the secondary cell wall? Not all plants... Produced only ... ..... than primary cell walls Provide more....
Not all plant have a secondary cell wall.
Produced only after cell growth has stopped
Thicker and stronger than primary cell walls.
Provides more structural support than primary cell wall.
Secondary Cell wall chemical characteristics
More Cellulose
Less Pectin
15-35% Lignin
What is the most abundant organic macromolecule
Cellulose
What is the second most abundant organic macromolecule
Lignin
