lecture 6 Flashcards
what are the two main types of polysaccharides in cell walls
hemicellulose and pectins
whats the most abundant macromolecule on earth
cellulose
what is cellulose monommer
glucose only
what are the two phases of making the primary cell wall
Phase one is the crystalline microfibrillar phase- cyrstaline as its so organised
Phase two is the non-crystalline matrix. Less organised, two sugar types
Pectin and hemicellulose
Protein called extensin
describe hemicellulose
Hemicellulose has a long glucose backbone with many small side chains, different side chain monomers. Relatively rigid
describe pectin
Pectin, not so strong, gel like, absorbs water, whats used to make jam. It has negative charged which allows it to absorb water
what controls the expansion of a cell.
Expansion of the cell wall is controlled by extensin protein cross linkage
how does extensin linking work
extensin crossing dehydrates the cell, making it less extensible and increases the cell strength. Extensin cross links pectin and cellulose.
whats the three main roles of the cell wall
Cell wall does 3 main things:
Influences cell morphology
Provides structural support
Prevents excessive water uptake, which prevents lysing
what does the middle lamella do
Middle lamella between cells sticks the adjacent cells together.
primary Cell wall synthesis: this involves the co-ordinated synthesis and delivery of 3 things and where are they made
1: cellulose microfibrils made at the plasma membrane
2: Pectin & hemicellulose made in the golgi, transported to the well in vesicles
3: Cell wall proteins, extensins, made in ER, vesicle transports this to the cell wall
whats a rosette
an enzyme filled structure. The enzymes in this sac are cellulose producing enzymes
how does a rosette work
This move through the plasma membrane parallel along the cortical microtubules, microtubules under the plasma membrane. The rosettes move along them creating cellulose fibres behind it.
If the microfibrils are oriented randomly
then the cell wall expands equally in all directions.
If the microfibrils are at right angles to the cell long axis
the cell will expand longitudinally a long said axis.
whats the protoplast
everything within the cell wall.
when does wilting occur
Wilting of cell wall occurs when the protoplast is shrunken and not pushing onto the cell wall. This occurs when not enough water is in the cell. As protoplast volume decreases protoplast pressure decreases.
difference between secondary cell wall and primary cell wall
2nd cell wall is formed once the cell has stopped growing. 2nd cell wall has ligand. 1st cell wall has more pectin and hemicellulose and less cellulose. 2nd has many layers of microfibrils
what does ligand do
Ligand is the second most abundant macromolecule:
Complex polymer
Acts to exclude water in the cell wall, contributing to its strength.
Confers the strength and rigidness of the cell wall.
Plasmodesmata does what
Creates intercellular connections which allow intercellular communication
These are big enough to allow small molecules, ions, to exchange between cells
Small enough to prevent organelles from moving across them, vesicles from rER do go through tho.
dry weigths of the cell wall
On dry weight cellulose is 40% weight of cell wall, hemicellulose is 20% pectins 30% and glycoproteins are 10% .
What is hemicellulose role?
(ii) Non-crystalline phase: Hemicellulose acts to bind cellulose microfibrils.
What are the two primary cell wall phases?
cyrstalline matirx: cellulose
and non crystalline matrix: hemicellulose and pectin
What is cellulose role
Crystalline phase: Cellulose microfibrils give the wall strength and flexibility.
What is Pectin role
(iii) Non-crystalline phase: Pectin acts as a glue (binds water to have gel-like properties).
what is Extensin’s role
(iv) Non-crystalline phase: Extensin (protein) controls the extensibility of cells through crosslinking cellulose and pectin.
plasmodesmata creates a what
continuous plasma membrane between cells.
why does a cell need energy
(i) Mechanical work (e.g. motor proteins)
(ii) Making new materials (e.g. for growth and replacement)
(iii) Transport (e.g. across membranes)
(iv) Maintaining order
what does the central vacuole do?
The vacuole regulates turgor pressure (together with the cell wall) within the cell allowing the plant cell to tolerate large changes in osmotic potential. This interplay of the two also determines cell shape. It also stores solutes and removes cellular wastes. A high tugor pressure gives plants their rigidity
whats the cell equivalent of the cytoplasm
the protoplast
what is the difference between the cytoplasm and the cytosol
cytoplasm is the fluid within the cell and all the organelles within the animal cell, cytosol is the fluid itself
