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Eukaryotic cell structure: support elements within the cell
- - Pressure from fluid (vacuole)
- - Cytoskeleton
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Eukaryotic cell structure: Cytoskeleton
- Network of fibers extending throughout the cytoplasm (its dynamic)
- Anchors many organelles, supports cell and maintains shape
- Regulate biochemical activities
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Cytoskeleton
Some organelles and vesicles move along the cytoskeleton: Motor proteins produce motility. -- Web like structures "acts as a highway"
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Cytoskeleton: Classified based on diameter
- Microfilaments (actin, myosin filaments) - thinnest
- Intermediate filaments - middle range
- Microtubules - Thickest
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Microfilaments #1
- Solid rods
- Twisted double chain of actin subunits (nanometer range)
- Near plasma membrane => cortex
- Anchored -->minus end
- Growing end --> plus end
- Can resist pulling/bear tension
- Moves organelles, change cell shape
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Microfilaments #2
- Different functions/shapes
- - Microvilli
- - Cytoplasmic contractile bundles
- - Lamillipodia and filipodia
- - Cell division contractile ring
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Microfilaments
Cytoplasmic streaming: Myosin moves organelles on a bed of actin (think of the moving chloroplasts)
- Myosin and actin filaments move past each other to shorten the muscle cell.
- Actin and myosin polymerize to form pseudopodium in amoeboid movement
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Intermediate Filaments
- Support cell shape and fix organelles in place. ex. nuclear lamina
- Do not polymerize and depolymerize very quickly - more permanent
- ex. keratin proteins
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Microtubules
- Hollow rods of tubulin
- Maintains cell shape, movement of cells, organelles and chromosomes
- Plus and minus ends
- - Grow by polymerizing tubulin at the plus end
- - In animals - start growing centrosome (near nucleus). => minus end is anchored
- - In plants - grows from microtubule organizing centre (MOC)
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Microtubules: Cilia and Flagella
- Specialized for beating
- * Cilia: power stroke and recovery stroke
- Can move liquid or air past a cell, or move the cell itself
- They have a core of mocrotubules surrounded by the plasma membrane
- Consists:
- - Outer microtubule doublet
- - Plasma membranes
- - Dynein proteins
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Microtubules: Cilium
- - Anchored with basal body --> cell membrance
- - 9 groupings of 2 microtubules => doublets
- - 2 of each basal body doublets extend out into cilium. Cilium - doublets
- - Additional pair in the middle (independently)
- Note: Cross section of basal body (similar in structure to centriole). Has 9 triplet microtubules groups arranged in a kind of pinwheel design.
- 9 doubles
- 2 singles
- 9 + 2 structure
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Microtubules: Cilia and flagella (cilium)
- Structure of cilia and flagella is a similar in many eukaryotes (paramecium and cells of windpipe cells)
- Motor protein - called DYNEIN - bends cilium
- Dynein anchored in doublet of tubules
- * Arms grab and move along another doublet (outer)
- Protein cross-links, limit sliding
- Cause doublets to curve, bending the cilium or flagellum
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Cytoskeleton: Multiple fibres in one cell type
- Intestinal microvilli
- - Microfilaments reinforce the microvilli, anchored to intermediate filaments
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Eukaryotic cell structure: connections of cells within tissues.
Extracellular
- Materials that are external to the plasma membrane
- Synthesized and secreted by the cell
- Connected to cytoskeleton via membrane proteins
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Extracellular matrix (ECM) Multicellular organism
- Network of material
- Secreted to outside of cell (sometimes in large amounts)
- Strong ex. animal skin
- Hold cells of a tissue together
- Provides support
- Cell signalling
- Fluid --> extracellular fluid
- Plants - cell wall
- Animals - glycoproteins (from rough ER) (collagen) in proteoglycan
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Parts of extracellular matrix
- - Extracellukar fluid
- - Collagen (the thickest strand)
- - The proteoglycan complex (look like the long thin branches that weave around the collagen)
- - The Fibronectin attached to the collagen on one end, and to the other the integrin
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ECM: Proteoglycan complex
- The main branch consists of a polysaccharide
- A side branch (proteoglycan molecule), the core is a protein, the little off shoots are carbohydrates
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ECM: Signalling
Collagen --> Fibronectin --> integrins --> cytoskeleton (microfilaments)
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Form and function in animal cell junctions
- 1. Prevent leakage (like skin): The plasma membrane of adjacent cells in close connection. This is done through specific proteins. Results ina continuous seal.
- => Tight junction
- 2. Join in strong sheets (like muscle cells): The intermediate filaments extend far into the cell.
- => Desmusomes/Anchoring
- 3. Chemical communication among cells in a tissue (intestinal cells): Membrane proteins of adjacent cells come together to make a pore.
- => Gap junction
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Plant ECM: Cell wall
- Cellulose micro fibres embedded in other polysaccharides and protein matrix
- Thin layer of polysaccharide (pectin) between primary walls of adjacent cells (middle lamella)
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Form and function in plant cell junctions
- Cytoplasm of one cell continuous with another through plasmodesmata (small passage way through the cell walls)
- Water, small solutes, some proteins can pass through, move along cytoskeleton
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Cell structure and function
- High rates of protein synthesis --> Fibosomes/nucleoli
- Movement --> cilia/flagella
- Energy consumption --> mitochondria
- Detoxification --> peroxisomes
- High turnover --> Lysosomes
- Storage: Vacuoles
- Steroid hormone production: Smooth ER
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Separating organelles for study: Fractionation
- Collect the tissue
- Homogenize: break up the cells - forms a homogenate
- Differential centrifugation (multiple steps): Cell components will fall to the bottom of the tube at speeds dependent on their size and mass
- Larger, heavier items form pellets at lower speeds
- Centrifuge each supernatant (the liquid on top of the debris in the tube) at a higher speed
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