Plant bio

• What are some differences of the plant cell compared to the animal cell?

  • Tonoplast
  • Chloroplast
  • Cell wall
  • Plasmodesmata
• Plant cells are glued together by a cell wall preventing cell migration
• Totipotency?

  The ability of a cell to divide and produce any cell type. I.e., a differentiated plant cell can be reprogrammed to form a different cell type.
• Are there many types of plant cells compared to animals?

  No, only around 50 types
• Movement within cells uses cytoplasmic screening (movement of cytoplasm), what is this process driven by?


  Driven by the motor protein myosin on microfilaments
• How are hundreds plant golgi stacks moved?

  Myosin on actin
• The fastest myosin is plant myosin XI, which takes 35nm steps.

  A) organelles

  B) adaptor

  C) tail

  D) Neck

  E) Motor

  F) Actin

  
• Chloroplasts move in response to light in leaf cells. How do chloroplasts arrange themselves in bright vs dim light?

  Dim light: chloroplasts align perpendicular to the direction of light to catch more light

  Bright light: chloroplasts align parallel to the direction of light to avoid being damaged by the high intensity of light
• chloroplast movement is triggered by what wavelength of light?

  Blue. Chloroplasts have receptors that respond to the light, and they move on actin filaments
• If there are no centrioles or centrosomes, how are microtubules made?

  Microtubules are made from microtubule organizing centers (MTOCs) located on the nuclear envelope
• What is part of the plant cytoskeleton and what is not?

  Plants have microtubules and microfilaments but no intermediate filaments. There are no centrioles or centrosomes but they have microtubule organizing centers instead.

  • MTs and ATs have associated proteins:
  • myosin and kinesin but no dynein
  • No cilia or flagella
• 4 microtubule arrays

  1. Cortical array: microtubules right up against the plasma membrane running parallel to the cell surface. They rapidly reorient in response in internal and external cues. Only array present in interphase.
  2. Pre-prophase band: transient band of MT important for cell division. Helps establish the plane of cell division by marking the future site of the cell plate
  3. Mitotic spindle
  4. phragmoplast: provides golgi-derived vesicles to the developing cell plate
• What is the cell wall made up of?

  Cellulose
• All plants have a what type of cell wall and some have a...?

  All have primary cell walls synthesized just outside the plasma membrane (extracellular).

  • some have a secondary cell wall synthesized after the primary one (inside the cell)
  • Rigid cells need a secondary cell wall to provide support
  • eg. xylem cells are rigid and need a secondary cell wall
• What does the middle lamella do?

  glues cells together using pectin
• What is cellular turgor pressure important for?

  Maintaining leaf shape and allows them keep an expanded open form that allows them to capture as much sunlight as they can
• what does the primary cell wall prevent from happening?

  Because the cells maintain a high internal turgor pressure, the primary cell wall prevents the cell wall from bursting due to the pressure
• what are cellulose microfibrils composed of?

  polymers of glucose
• What does expansin do?

  Breaks the hydrogen bonds between cellulose and hemicellulose
• What does extensin do?

  Holds cell wall components together
• Components of a cell wall

  1. cellulose microfibrils: polymers of glycosyl subunits bundled together by β- 1,4 linkages
  2. hemicellulose: linear polymers of glucose + one other sugar that crosslink adjacent microfibrils together using hydrogen bonds (reversible).
  3. Pectins: determine the porosity of the wall i.e., how dense the wall and how well things can move through. The more pectin, the less coarse. Pectins also bind proteins
  4. Proteins; role in cell stability and loosening other components
• Numerous rosettes synthesize a single cellulose microfibrils in the plasma membrane. Each rosette has 6 subunits cellulose synthase that work by pulling glucose from inside and bundling it, thus making the cellulose microfibrils. The microtubule guides the direction/movement of the cellulose synthase
• Hemicellulose and pectin synthesis

  • Made in the Golgi cisternae stacks
  • Deposited into vesicles at TGN
• What are in the vesicles that are deposited into the cell wall

  hemicellulose, pectin, and proteins are in the vesicles that are to be deposited into the plasma membrane so that all components may be delivered to the cell wall
• Elongation on one side of the plant will cause it to bend to the other side
• mitosis

  interphase: non-dividing

  prophase: chromosomes condense

  metaphase: condensed chromosomes line up at equator

  anaphase: sister chromatids separate

  telophase: new nuclear envelopes begin to form
• How does a root cell elongate?

  They can't stretch laterally but can vertically (like a slinky). It takes a combination of turgor pressure, cell wall loosening, and the orientation of cellulose microfibrils

  • much of plant growth is cell elongation not cell division
• Label stuff lol

  A) Preprophase bands

  B) cell plates

  
• When the preprophase bands bands appear, the cell is committed to cell division
• Cytokinesis

  • Cell plate matures, making a new cell wall.
  • preprophase band: transient band of MTs that predicts the plane and position of new cell wall
  • Does this by forming right under ('touching') the plasma membrane and leaving a footprint on the plasma membrane from the pressure. The footprint then becomes the attachment point of the cell wall. When cytokinesis occurs, the new cell wall will develop precisely at this marked location, ensuring proper cell separation.
• Phragmoplast development

  • Double membrane microtubule: MTs are orientated so their (+) ends facing each towards the center (midline) so the materials are delivered to the middle by kinesins
  • Role is to provide Golgi-derived vesicles to the developing cell plate that grows outwards until it fuses with the plasma membrane, separating the two daughter cells
• Plasmodesmata

  Cytoplasmic connections between adjacent cells

  • unique to plants (analogous to gap junctions)
  • 10x larger openings than gap junctions
  • move small (passively) and large molecules (selectively moved)
  • present in virtually all plant cell types - plants are sometimes call "supra cellular" organism because all cell of a plant are connected
• structure of plasmodesmata

  • Desmotubule: central tubule found within a plasmodesmata providing structural support and possibly helping the plasmodesmata be more specific for size and types of molecules
  • Spoke-like extension: proteins that extend from desmotubule that act like a filter
  • Cylinder of cytoplasm that goes around
• plasmodesma formation?

  Forms during cell division when each cell plate is formed and ER is trapped in the new cell wall. These trapped ER portions contribute to the formation of plasmodesmata, which are channels that connect neighboring plant cells and facilitate communication and transport between them.
• Plasmodesma have a natural size exclusion limit that restricts what can passively move through


  For most things, limit is 1kDa. But macromolecules can selectively move using a signal.

  • signal = protein that 'opens the gate' allowing movement of larger molecules
• vacuoles

  Fluid filled organelle surrounded by its own membrane called the tonoplast. Can take up to 90% of cell volume but typically takes up 30%.

  Function:

  1. contains lots of solutes used to maintain turgor pressure
  2. Storage: stores ions, organic acids, sugars, and proteins
  3. Digestion: 'dump site' - materials moved into vacuoles for degradation. Contain degradation enzymes.
  4. pH and ion homeostasis: typical vacuoles are acidic
  5. defense: plants can store toxic compounds in vacuoles. Vacuoles can then burst to release the toxic compounds
• What are the two types of vacuoles?

  1. Lytic vacuoles: performs most basic vacuole functions (storage, degradation, etc.)
  2. Protein storage vacuole: stores proteins that can be used as food reserves