1. Cytoskeleton, Cell Walls, & ECM
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Cytoskeleton, Cell Walls, & ECM

2. Cytoskeleton – network of fibers extending throughout the cytoplasm

5. MICROTUBULES FUNCTION Structural support and cell movement
~ Move chromosomes during cell division
Centrioles & spindle fibers
~ tracks guide motor proteins
Motor proteins: dynein & myosin
~ cell motility
Cilia & flagella

7.
MICROTUBULES
Tracks guide motor proteins to destination (Motor proteins: dynein & myosin)
Vesicle
Receptor for
motor protein
Motor protein
(ATP powered)
Microtubule
of cytoskeleton
ATP
SEE MOTOR PROTEINS in ACTION
EXAMPLES
Vesicles containing neurotransmitters migrate to tips of nerve cells
Vesicles move to Golgi along cytoskeletal tracks
Cytoplasmic streaming

8. Cilia and Flagella Are locomotor appendages Extensions of cytoskeleton
Examples:
Many unicellular protists move with flagella
Some plant reproductive cells have flagella
Cilia in oviducts move egg toward uterus
Cilia lining windpipe sweep mucous out of lungs
Flagellum in sperm cells
(Prokaryotic flagella don’t have microtubules)

9. Cross section of basal body
Cilia and flagella share a common ultrastructure
(b)
Outer microtubule
doublet
Dynein arms
Central
microtubule
Outer doublets
cross-linking
proteins inside
Radial
spoke
Plasma
membrane
Microtubules
Basal body
0.5 µm
0.1 µm
Cross section of basal body
Triplet

10. FLAGELLUM (few, long) whip-like movement; cell moves in same direction as axis of flagellum
CILIUM (many, short) oar-like movement; cell moves perpendicular to axis of cilium

12. MICROFILAMENTS STRUCTURE Thinnest class of fibers
Twisted double chain of actin subunits
~ 7 nm in diameter
FUNCTION
Crosslinks with microtubules (cell shape)
Muscle cells: Actin filaments interact with myosin motor proteins to create muscle contraction
Amoeboid movement
Cytoplasmic streaming

13. MICROFILAMENTS Make up contractile apparatus of muscle
Contain the motor protein myosin in addition to actin
Actin filament
Myosin filament
Myosin motors in muscle cell contraction.
(a)
Muscle cell
Myosin arm

14. Amoeboid movement
Actin filaments constantly form & dissolve making cytoplasm liquid or stiff during movement
Cortex (outer cytoplasm):
gel with actin network
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium

15. Cytoplasmic streaming
Speeds distribution of materials
Nonmoving
cytoplasm (gel)
Chloroplast
Streaming
cytoplasm
(sol)
Parallel actin
filaments
Cell wall

16. NUCLEAR LAMINA

19. Cell Walls of Plants Protection Maintain shape
Also found in Prokaryotes, fungi, and some protists
Composition varies with species/cell type
Basic design:
Microfibrils of polysaccharide cellulose embedded in matrix of other polysaccharides
(like steel reinforced concrete)

20. MIDDLE LAMELLA- ~ between primary cell walls of adjacent cells
Plant cell wall Structure
PRIMARY CELL WALL
MIDDLE LAMELLA- ~ between primary cell walls of adjacent cells
~ made of sticky polysaccharides (pectins)
~ glues cells together
SECONDARY CELL WALL
~ built when cell stops growing ~ between plasma membrane and 1° cell wall

21. Unify plant into one living continum

24. Types of intercellular junctions in animals
TIGHT JUNCTIONS Membranes of neighboring cells and pressed together & bound by proteins
Forms continuous seal to prevent leakage of extracellular fluid across layer of cells
DESMOSOMES (anchoring junctions)
Act like “rivets” to fasten cells together into strong sheets
Intermediate proteins (keratin) anchor desmosomes in cytoplasm
GAP JUNCTIONS (communicating junctions)
Channels connect to adjacent cells
Special membrane proteins surround pore
Necessary for communication between cells in heart muscle and animal embryos

25. The Cell: A Living Unit Greater Than the Sum of Its Parts
Cells rely on the integration of structures and organelles in order to function
5 µm
Figure 6.32