Exams Based on Altamish's notes Flashcards
Role of Microtubules vs. Actin Filaments in Plant Cells (Similarities)
3 similarities between microtubules vs actin filaments in plant cells
- both serve as tracks for movement of organelles and vesicles within the cell. Motor proteins (kinesins for microtubules and myosins for actin) move along these filaments to transport cellular components.
- Microtubules and actin filaments undergo constant assembly and disassembly, which is essential for their function in growth, division, and response to environmental changes.
- Both cytoskeletal elements play key roles in shaping the cell. Actin aids in cell expansion, while microtubules direct the orientation of cellulose fibers in the cell wall, affecting overall cell shape.
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Role of Microtubules vs. Actin Filaments in Plant (Differences)
3 differences between microtubules and actin filaments in plant cells
Microtubules: Composed of α- and β-tubulin dimers that form hollow tubes, for rigidity and strength.
Actin Filaments: Made of actin monomers (G-actin) polymerized into thin, flexible strands (F-actin).
Microtubules: guide cell division and determining the plane of division and direct the positioning/orientation of cellulose synthase for cell wall deposition.
Actin Filaments: involved in cytoplasmic streaming, endocytosis, and polar cell growth by facilitating vesicle movement and organelle distribution.
Microtubules: Form structures such as the pre-prophase band, spindle apparatus, and phragmoplast, essential for stages of cell division.
Actin: not directly involved in division, actin filaments maintain cell shape and distribute organelles and vesicles to daughter cells.
Role of Cellulose and Hemicellulose in the Plant Cell Wall
similarities between cellulose and hemicellulose
both integrate into cell wall matrix, support structural integrity.
both allow for controlled cell expansion. Hemicellulose cross-links cellulose fibers, maintaining wall flexibility, structure and growth.
Role of Cellulose and Hemicellulose in the Plant Cell Wall
differences between cellulose and hemicellulose
Structural
Cellulose: Forms linear microfibrils that are primary load-bearing structure in cell wall for tensile strength
Hemicellulose: Cross-links cellulose microfibrils, adds flexibility to cell wall, maintain cell wall integrity during expansion.
Synthesis and Organization:
Cellulose: Synthesized at PM via cellulose synthase.
Hemicellulose: Synthesized in the Golgi, transported to cell wall in vesicles, to integrate with cellulose microfibrils.
Chemical Composition:
Cellulose: Composed solely of β-1,4-linked glucose units.
Hemicellulose: Made up sugar monomers, including xylose, mannose, and arabinose, a branched, complex structure.
Role of the Golgi in Polar Tip Growth and Cell Wall Development
similarities between golgi in polar tip growth and cell wall development
For both, Golgi packages cell wall materials and enzymes into vesicles and directs to areas requiring growth or maintenance or need
For both, Golgi synthesizes polysaccharides (like pectin and hemicellulose) for general cell wall and specific growing regions, ensuring structure integrity
Role of the Golgi in Polar Tip Growth and Cell Wall Development
differences between golgi in polar tip growth and cell wall development
Polar Tip Growth: Golgi directs vesicles specifically to the cell’s tip (e.g., root hair or pollen tube) for localized, targeted growth.
Delivers pectin and membrane components to extend the tip.
Cell Wall Development: vesicles are delivered to multiple sites along the cell wall, enabling even maintenance across entire cell
Delivers cellulose synthase, hemicellulose, and structural proteins for wall reinforcement
Production, Dynamics, and Structural Characteristics of Actin and MTs
differences between both
production: actin filaments, thin and flexible, (F actin) is formed by polymerizing actin monomer units (G actin)
dynamics: highly dynamic, constantly undergoing assmebly and dissassembly, rapidly redeveloping cytoskeleton in response to environment
structure: thin flexible filaments (F actin) that forms bundles that concentrate at cell cortex, involved in cytoplasmic streaming and cell expansion
Production: formed by the polymerization of α- and β-tubulin dimers, which assemble into hollow tubes for rigidity and strength
Dynamics: undergo constant assembly and disassembly, rapidly growing and shrinking, has dynamic instability. This is regulated by MAP proteins (Ex: MAP 4 binding protein)
Structure: alpha, beta tubulin dimers that form hollow tubes for structural support, rigidity, serve as tracks for organelles to move on ( via motors like kinesin). Forms essential structures like phragmoplast, spindle apparatus in cell division
2 processes that utilize MTs
2 processes that utilize MTs
Cell Division: MTs form pre-prophase band and mark division plane, ensuring alignment of daughter cells. In mitosis, the spindle apparatus organizes and separates chromosomes, while the phragmoplast directs vesicle delivery to the cell plate.
Vesicle Transport for Cell Wall Assembly:
MTs guide transport of Golgi vesicles containing cell wall materials, ensuring that vesicles are accurately delivered to sites where wall remodeling or growth is required. This is crucial in areas like the expanding cell plate during cytokinesis.
2 processes that utilize actin
Cytoplasmic Streaming:
Actin filaments facilitate flow of cytoplasm, allowing organelles, nutrients, and signaling molecules to move throughout large plant cells. important in vacuolated cells where diffusion alone would be inefficient.
Polar Tip Growth:
Actin filaments transport vesicles carrying cell wall materials to the growing tips of cells like root hairs and pollen tubes. Actin-based transport supports localized growth at the tip, essential for nutrient absorption and reproductive success.
