topic 5

• All physiological processes depend on movement
• Intracellular transport
• Changes in cell shape
• Cell motility
• Animal locomotion
• All movement is due to the same cellular "machinery"
• Cytoskeleton is a protein-based intracellular network
• Motor proteins are enzymes that use energy from ATP to move
• Cytoskeleton elements for movement include:
• Microtubules
• Microfilaments
• Microtubules are tubelike polymers of the protein tubulin
• They are anchored at both ends
• Microtubule-organization center (MTOC) is near the nucleus
• Tubulin is a dimer of a-tubulin and b-tubulin
• Microtubules have polarity with a minus (–) end and a plus (+) end
• Cilia:
• Numerous, wavelike motion
• Flagella:
• Single or in pairs, whiplike movement
• Composed of microtubules arranged into axoneme
• Nine pairs of microtubules around a central pair in the "nine-plus-two" arrangement
• Microfilaments are polymers composed of the protein actin
• They are found in all eukaryotic cells
• Movement arises from actin polymerization and sliding filaments using myosin
• Sliding Filament Model:
• Actin is analogous to the rope, and myosin is analogous to your arm
• The cycle involves grasp, pull, and release actions
• The Skeletal System:
• Supports and protects the body
• Transmits mechanical forces generated by muscles
• Exoskeletons:
• Nonliving skeleton characteristic of mollusks and arthropods
• Arthropods must molt periodically as the exoskeleton doesn't grow
• Endoskeletons:
• Consist of living tissue and can grow
• Found in echinoderms and chordates
• Hydraulic Skeleton:
• Fluid in a closed body compartment transmits forces generated by contractile cells or muscle
• Found in soft-bodied invertebrates like cnidarians, flatworms, and annelids