Lecture 8 Flashcards
What is the plant cell wall mainly made up of
Microfibrils made of cellulose
What are microfibrils
Highly organized structures made of cellulose.
What are the two phases of cell wall structure
Microfibrils (Crystalline Phase)
- Cellulose
Matrix (non-crystalline matrix)
- Pectin polysaccharides
- Hemicellulose polysaccharides
(+ a network of Extensin which is 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.
What is Pectin
branched, negatively charged
polysaccharides. Bind water and have
gel-like properties.
What two parts make up the matrix of the cell wall
Hemicellulose and Pectin
What is the function of extensin
It controls the expansion of cells through extensin cross-linking
How does extensin cross-linking control the explansion of cells
Extensin cross-linking of pectin and cellulose dehydrates the cell
wall, reduces extensibility and increases strength
Where are cellulose microfibrils synthesized
At the plasma membrane
Where are the polysaccharides pectin and hemicellulose synthesised
In the golgi complex. They are transported to the plasma membrane in vesicles
Where is extensin sythesised
In the rough ER and then transported in vesicles which fuse with the plasma membrane
What is a cytoskeleton
A network of microtubules and microfilaments and intermediate filaments that extend through the cytoplasm
what is cellulose synthase and where is it found?
It is an enzyme that is embeded in the plasma membrane of the cell wall.
What does cellulose synthase come together to form
They group together to form a rosette
Where are microtubules found on the plasma membrane and what are they connected to
They are found on the inside of the Plasma membrane and are connected to the rosettes of Cellulose synthase
What connects cellulose
Hemicellulose
What is the function of pectin
High amounts of pectin glue together cell walls of adjacent cells
What is tugor pressure
The protoplast pushes against the cell wall and prevents excessive water uptake
Vacuoles are important in this process
because they contain water and make
up such a large portion of the protoplast.
What is the function of the vacuole
Water uptake via osmosis, limits uptake and prevents the cell bursting
builds up tugor pressure that contributes to plant structural support
Why do microfibrils in each layer of the cell wall have different orentations
Because this strengthens the cell wall
What are 3 chemical characteristics of the secondary cell wall
More cellulose
Less pectin
Ligin
What is ligin and what is its function
Complex polymer. It confers stregnth and rigitity to the secondary wall and acts to exclude water
What are Plasmodesmata
Plasmodesmata are intercellular connections, that enable cell to
cell communication.
What cellular structure could viruses use to travel from one plant
cell to another?
Plasmodesmata
