cell walls & their role in regulating plant cell shape Flashcards
what are the components of the plant cell?
- nucleus
- endomembrane reticulum
- Golgi apparatus
- mitochondrion
- central vacuole
- chloroplast
- cell wall
- plasmodesmata
a plant cell = ?
the cell wall + the protoplast
what are the components of the cell wall structure cellulose?
- The most abundant organic macromolecule on Earth
- Glucose polymer
- Highly ordered
- Long, ribbon-like structures
what does cellulose form?
microfibrils
- highly organized structures are strong and form a
a major component of both primary and secondary cell walls
what are the two phases in the cell wall structure?
Phase 1: Crystalline Microfibrillar Phase
- Cellulose
Phase 2: Noncrystalline Matrix
- Pectin polysaccharides
- Hemicellulose polysaccharides
- plus a network of Extensin (a protein)
what is hemicellulose?
- A hemicellulose is a heterogeneous group of polysaccharides.
- Long chains of one type of sugar and short side chains form a rigid structure.
what is pectin?
- Pectin branched, negatively charged polysaccharides.
- Bind water and have gel-like properties
what happens in the cell wall structure: the protein extensin?
- The extensibility (expansion) of cells can be controlled by extensin cross-linking
- Extensin cross-linking of pectin and cellulose dehydrates the cell wall, reduces extensibility, and increases strength
what happens during the coordinated synthesis and delivery of synthesis of the Primary Cell Wall?
- Cellulose microfibrils at plasma membrane
- Polysaccharides (pectin & hemicellulose) in the Golgi apparatus are transported to the wall in vesicles.
- Cell wall proteins (extensins) from the rough ER.
- The vesicles fuse to the plasma membrane
what happens during exocytosis?
- Transports material out of the cell or delivers it to the cell surface
- Constitutive exocytosis releases extracellular matrix proteins
what is the protoplast?
plasma membrane+all the organelles+cytoplasm that sit inside the plasma membrane
what is a cellulose-producing rosette?
- is a protein complex enzyme
what is a cellulose-producing rosette?
- is a protein complex enzyme
- The cellulose-producing rosettes move parallel to the
cortical microtubules
what does the cellulose-producing rosette do?
- sits across the plasma membrane + joins together glucose molecules = to make cellulose
- The cellulose-producing rosettes move parallel to the
cortical microtubules
what determines the cell wall shape?
Where the cortical microtubules are = cellulose producing enzyme attaches = position of microtubules determine = cellulose laydown = determines the cell shape
what happens with the cortical microtubules?
cortical microtubules are right up against the plasma membrane associated with this is the rosette that makes the cellulose = goes all the way down = rosette goes with it = as it goes along produced cellulose microfibril
what is the primary cell wall?
- primary cell wall
- middle lamella
- pectin
- cellulose
- hemicellulose
what is the middle lamella?
- above the cell wall
- mostly pectin (sticky substance)
- stick cells together
cellulose forms microfibrils that are highly ordered and provide strength to the cell wall (true or false)?
true
extensins cross-links polysaccharides this increases the extensibility of the cell (true or false)?
false
pectin and hemicellulose are transported to the cell surface by exocytosis (true or false)?
true
what is the cell walls’ function that helps with regulating the cell shape?
- influences cell morphology
- provides structural support
- prevents excessive water uptake
what is cell morphology?
- Orientation of the cellulose microfibrils influences cell morphology
what are the two types of cell morphology?
- Randomly oriented - The cell will expand equally in all directions
- Right angles to the ultimate long axis of the cell - the cell will expand longitudinally along that axis.
how does the cell wall provide structural support?
-The protoplast pushes against the cell wall. The cells become rigid and this maintains the plant structure
- Wilting occurs when the protoplast is not pushing against the cell wall.
- Water loss from cells reduces the protoplast volume and the protoplast does not press on the cell wall
how does the cell wall prevent excessive water intake?
- As water enters the cell by osmosis, the protoplast expands and pushes against the cell wall.
- Pressure from the cell wall limits the volume of water that can be taken up
- Vacuoles are important in this process because they contain water and makeup such a large portion of the protoplast
what is the structure of the vacuoles?
- It is highly selective, controlling much of what enters and leaves the vacuole
- Water moves in the vacuoles by osmosis (passive transport)
what is a vacuole?
A vacuole is an organelle surrounded by a single membrane
- Typical mature plant cell has a single large vacuole
what is the vacuole function in the regulation of cell shape?
- There are high concentrations of solutes in the vacuole
- This results in water uptake into the vacuole by osmosis
- The plant cell wall limits water uptake and prevents the cell from bursting.
- Plant cells build up a large internal pressure that contributes to plant structural support.
what is osmosis?
The diffusion of water across a selectively permeable membrane (around the vacuole for plants)
how does the movement in osmosis work?
High water (low solute) concentration
to
Low water (high solute) concentration
what is really important for managing water uptake?
pressure against the cell wall = if no cell wall water would keep being taken up by osmosis and it would brust
in the cell wall, carbohydrates are diverse and functional important molecules (true or false)?
true
what is the secondary cell wall?
- Produced only after cell growth has stopped
- Thicker and stronger than primary cell walls
- Provides more structural support than the primary cell wall
what is the structure of the secondary cell wall?
- Made up of multiple layers
- Microfibrils in each layer have different orientations
- This strengthens the secondary wall
what are the chemical characteristics of the secondary cell wall?
- More cellulose
- Less pectin
- Lignin
what is lignin in the secondary cell wall?
- Lignin is the second most abundant organic macromolecule
- Lignin is a complex polymer
- Confers strength, rigidity to the secondary cell wall and acts to exclude water
what does the secondary cell wall provide structural support for?
specific cell types - such as water transporting cells, and for the whole plant
what are plasmodesmata?
Plasmodesmata are intercellular connections, that enable cell-to-cell communication.
what do plasmodesmata do in terms of cell communication?
- The plasma membrane is continuous
- Small enough to prevent organelle movements – although the endoplasmic reticulum is connected through plasmodesmata.
- Allows the free exchange of small molecules
what is closer to the cell?
secondary cell wall
