Cell wall and plant cell shape - L7 Flashcards
What is found in plant cell walls?
Chem energy is stored in plants in the form of carbs, found in cell walls that keep it strong and give it shape.
Plant cell components
Cell wall + protoplasts (cell membrane + organelles extras vacuoles, chloroplasts and plasmodesmata)
What are cell walls made of?
Cellulose, long ribbon like structures that is highly ordered, made from 1-4 linkages of ß glucose monomers, held together by glycosidic linkages
How is cellulose structured?
Cellulose ribbons forms bonds with other ribbons to form microfibrils, which is a key component of primary and secondary cell walls
Phase 1
Is a Crystalline microfibular phase made of cellulose
Phase 2
3 parts - non-crystalline matrix
*Hemicellulose polysacch
*Pectin Polysacch
*Extensin protein
Hemicellulose
*Long chains of one sugar and then side chains of different sugars to form a rigid structure, heterogenous groups of polysacch
Pectin
Branched structures of negatively charged polysaccharides. Its negative charge allows it to bond with H2o and has a gel/jam like properties i.e sticky, it is not very stronk
Extensin
Controls the extensibility of the cell wall
*When cell wall is laying down its foundation of sugars, the extensin is randomly placed so the water in the cell causes the cell to expand against the cell wall, also causes the cell wall to expand
*When cell stops growing, the extensin cross links with the pectin and cellulose, causes loss of water and dehydration = rigid and strong structure
Cell wall synthesis (1)
Glucose from inside the cell is linked together by an enzyme complex called a Rosette, which sits and moves across the plasma membrane surface. It links the Glucose and releases and lays down the cellulose microfibrils that run vertically and horizontally.
Rosette moves along a cortical microtubule right under the plasma membrane
Polysaccharides
Pectin and Hemicellulose made in the Golgi apparatus and transported through vesicles - constitutive exocytosis
Extensin
Made in the rough ER and transported through vesicles, fuses with the plasma membrane and contents gets pushed out to the cell wall - constitutive exocytosis
Cytoplasmic streaming
The chloroplasts move around the exoskeleton to maximise the exposure of chloroplasts to the sun
Functions of the cell wall
*Cell morphology
*Cell structure
*Uptake of H2O
Cell morphology
Depends on how cellulose microfibrils are layed down (by the rosettes along the CORTICAL MICROTUBULES). If its random, cell expands uniformly.
If its at right angles, cell expands to that shape due to pressure from microfibrils.
Cell wall structure
The protoplasts (at turgid) push up against the cell wall and give it structure and rigidity
At water loss, the volume of H2O decreases so protoplast volume decreases, causing cell mem to pull away from the cell wall, and no more pressure causes it to wilt.
Prevents h2o uptake
The pressure from the cell wall at rigidity prevents more water to be taken in through osmosis
Vacuole
Makes up the biggest part of the protoplast and is mostly H2O
Mostly H2O because it has a high conc. of solutes so H2O moves across the semi-permeable membrane to balance out osmotic equilibrium for structural support.
2º cell wall
Made of more layers of cellulose, thick, in between cell membrane and 1º, not found in all plant cells
3 layers of cellulose that are oriented differently for maximum support
More cellulose
Less jammy pectin
Lignin!
Lignin
2nd most abundant macromolecule, complex polymer, excludes H2O so hard to break down cell wall with H2O and enzymes for E.
