Biology 1020 lecture 8 Cell structure 3

• - Pressure from fluid (vacuole)
• - Cytoskeleton

• Network of fibers extending throughout the cytoplasm (its dynamic)
• Anchors many organelles, supports cell and maintains shape
• Regulate biochemical activities

Some organelles and vesicles move along the cytoskeleton: Motor proteins produce motility. -- Web like structures "acts as a highway"

• Microfilaments (actin, myosin filaments) - thinnest
• Intermediate filaments - middle range
• Microtubules - Thickest

• 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

• Different functions/shapes
• - Microvilli
• - Cytoplasmic contractile bundles
• - Lamillipodia and filipodia
• - Cell division contractile ring

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

• Support cell shape and fix organelles in place. ex. nuclear lamina
• Do not polymerize and depolymerize very quickly - more permanent
• ex. keratin proteins

• 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)

• 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

• - 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

• 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

• Intestinal microvilli
• - Microfilaments reinforce the microvilli, anchored to intermediate filaments

• Materials that are external to the plasma membrane
• Synthesized and secreted by the cell
• Connected to cytoskeleton via membrane proteins

• 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

• - 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

• The main branch consists of a polysaccharide
• A side branch (proteoglycan molecule), the core is a protein, the little off shoots are carbohydrates

Collagen --> Fibronectin --> integrins --> cytoskeleton (microfilaments)

• 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

• Cellulose micro fibres embedded in other polysaccharides and protein matrix
• Thin layer of polysaccharide (pectin) between primary walls of adjacent cells (middle lamella)

• 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

• 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

• 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