Lecture 7 - Cell Walls And Their Role In Regulating Plant Cell Shape Flashcards
What is a protoplast?
The plasma membrane and everything inside the membrane.
What are plant cell components?
The cell wall and the protoplast.
What is cellulose?
A highly ordered glucose polymer that forms long ribbon-like structures. It is the most abundant organic macromolecule on earth.
What is the major component of the cell wall?
Cellulose. It’s properties are good for structure of the cell wall
What does cellulose form?
Cellulose forms microfibrils. The ribbons of cellulose line up next to each other and cross link, forming the microfibres.
What are the two phases of cell wall structure?
Phase 1: crystalline microfibrillar phase - cellulose
Phase 2: Noncrystalline matrix - pectin polysaccharides and hemicellulose polysaccharides
+ network of extensin (a protein)
What is hemicellulose?
A heterogeneous group of polysaccharides. Long chain of one type of sugar and short side chains form a rigid structure
(Not as strong as cellulose)
What is pectin?
Branched negatively charged polysaccharides.
What are the properties of pectin?
Pectin binds water and is gel like. It sticks on top of other polysaccharides.
What does extensin cross linking with pectin and cellulose do?
Dehydrates the cell wall, reduces extensibility and increases strength
What is extensibility of cell controlled by?
Extensin cross linking
What is the steps of synthesis of the primary cell wall?
1) cellulose microfibrils are laid down at the plasma membrane
2) The polysaccharides (pectin and hemicellulose) are transported from the golgi complex to the plasma wall in vesicles.
3) cell wall proteins (extensins) are released from the rough ER and are released out of the cell
What is a rosette?
An enzyme complex (cellulose synthase) that pushes through the entire cell from inside to outside.
Why are microtubules the most important in context to making the primary cell wall?
Because the microtubules close to the plasma membrane will help lay down the cell wall. It is important for knowing where to put the cellulose, thus controls shape of cell.
Why is it important to have cytoplasmic streaming?
So the chloroplast move around the cell to maximise photosynthesis/get an even amount of light
Describe the relationship between rosettes and microtubules
The rosette associates with the microtubule. Because the plasma membrane is dynamic, the rosette can move along the microtubule and produces cellulose microfibril.
What is the middle lamella made out of and what does it do?
The middle lamella is made of pectin so it is gel like and it sticks stuff together
What is in the primary cell wall?
Pectin
cellulose
hemicellulose
What does the cell wall do?
Influence cell morphology
Provide structural support
Prevent excessive water uptake
What influences cell morphology
The orientation of the cellulose microfibrils influences cell morphology
Describe the two different orientations of cellulose microfibrils
a) randomly orientated - when randomly orientated the cell will expand equally in all directions meaning that the cellulose will have equal pressure
b) right angles to the ultimate long axis of the cell - The cell will expand longitudinally along that axis. (When expanding it is hard to push it in other ways)
How does the cell wall provide structural support?
When the protoplast pushes against the cell wall. This makes the cell become rigid and makes it maintain its structure.
What happens when there is water loss from the cell?
When water is lost from the cell, the protoplast will lose volume causing it to be unable to push on cell wall.
How does the cell wall prevent excessive water uptake?
When water enters the cell by osmosis the protoplast expands and pushes against the cell wall. The pressure created from the cell wall limits the volume of water that can be taken up.
Why are vacuoles important in preventing excessive water uptake?
Because the vacuole contains water and makes up a large portion of the protoplast.
What is the structure of a vacuole?
The vacuole is an organelle surrounded by a single membrane.
Describe the single membrane of the vacuole
The membrane is highly selective and controls much of what enters and leaves the vacuole.
Describe the vacuoles function in regulation of cell shape
Due to the high concentration of solutes in the vacuole, there is water uptake by osmosis. The plant cell wall limits the amount of water uptake to prevent the cell from bursting which builds up a large internal pressure that contributes to plant structural support.
What is the secondary cell wall?
The secondary cell wall is produced after cell growth has stopped. It provides more structural support than the primary cell wall because it is thicker and stronger.
Not all plant cells have a secondary cell wall.
Describe the physical structure of the secondary cell wall.
The secondary cell wall is made up of multiple layers of cellulose with the microfibrils in each layer having different orientations which strengthens the secondary cell wall.
Describe the chemical characteristics of the secondary cell wall structure
The secondary cell wall has more cellulose, less pectin and has lignin.
What is lignin and what is its function?
Lignin is a complex polymer that confers strength and rigidity to the secondary cell wall and acts to exclude water.
What does the secondary cell wall provide structural support for?
It provides support for specific cell types such as water transporting cells and for the whole plant.
How do you cells with a cell wall communicate?
Through the plasmodesmata.
What is the plasmodesmata?
The plasmodesmata are intercellular connections that enable cell to cell communication.
How does the plasmodesmata work?
The plasma membrane is continuous so through the use of the plasmodesmata, free exchange of small molecules is allowed but because the plasmodesmata is small it prevents organelles to move besides parts of the ER that can poke through.
