Chapter 9 Flashcards
What is the cytoskeleton?
Known as the skeletal system of eucaryotic cells
What is the cytoskeleton composed of?
Microtubules, actin filaments, and intermediate filaments
Functions of cytoskeleton components
- Provide structural support and maintain cell shape
- Positions various organelles in the cell
- Direct movement of material and organelles within cell
- Generates force is needed for cellular locomotion
- Makes up important part of cell division machinery
Describe the structure and composition of microtubules
Hollow, relatively rigid, tubular, assembled from protein
How are microtubule proteins arranged?
Longitudinal rows called protofilaments
What are protofilaments?
Assembled from dimeric building blocks consisting of one alpha tubulin and one beta tubulin subunits
What is the function of microtubule associated proteins?
Increased ability and promote microtubule assembly by linking tubulin subunits together
What are the functions of microtubules?
Service tracks for variety of motor proteins that generate force is required to move objects within a cell
Three super families of microtubules
Kinesin and dyeins, myosin
What is Kinesin?
Tetramer of two identical heavy and two identical light chains, smallest and best understood microtubule motor
Globular heads bind microtubules and act as what?
ATP hydrolyzing, force generating engines
Kinesin movement is like:
Hand over hand mechanism
What is cytoplasmic dynein?
Huge protein, two identical heavy chains, variety of intermediate and light chains
Cytoplasm dynein moves how?
Along microtubule toward polymers minus end, positions centrosome and Golgi complex
Cytoplasmic dynein purpose is what?
Moves organelles, vesicles, and particles through cytoplasm
What do microtubule organizing centrecontrol?
- Number of microtubules
- Polarity of microtubules
- Number of protofilaments
- Time and location of assembly
What is a centrosome?
Major sight of microtubule initiation in animal cells and remains at centre of cells in microtubule Netwerk
What is a basal body?
Another type of MTOC that forms a base of cilium or flagellum, can turn into centrioles
Can microtubule shorten, lengthen, disassemble, and reassemble?
Yes
What is microtubule stability determined by?
Interacting proteins
Disassembly of microtubules can be initiated by what?
- Post translational modification
- Cold temperature
- Hydrostatic pressure
- Elevated calcium
- Variety of chemicals
Describe cilia
Hair-like, sometimes motile organelles, project from surface of a variety of eucaryotic cells
What is motile cilia?
Usually occurs in large numbers, coordinated beating activity to induce movement
Describe flagella
Typically occur singly or in parts and exhibit a variety of beating patterns
What is axoneme?
Core of cilium, contains an array of microtubules
Each axoneme contains what?
Peripheral doublets with an a tubule, central tubules enclosed by central sheath 
Cilium and flagellum emerge from what?
A basal body
What are intermediate filaments?
Strong, flexible, ropelike fibres that provide mechanical strength to cells that are subjected to physical stress
How many major classes of intermediate filaments?
5
What are keratin containing IFs?
Structural proteins of epithelial cells
What are keratin containing IF function?
Organize and maintain cellular architecture and absorb mechanical stress
What are neurofilaments?
IFs located in cytoplasm of neurons in bundles oriented parallel to axon
Acton filaments are organized into what?
- Ordered arrays
- Highly branched networks
- Tightly anchored bundles

Actin filament structure
Do stranded structure with two helical grooves running along its length
Actin filaments are pointed in the same direction resulting in what?
Polar filament
What is a major contractile muscle protein?
Actin
What is myosin?
Molecular motors that operate in conjunction with actin filaments, moves towards barbed end of Acton
Head of myosin contains what?
- A site that binds an actin filament
- A site that binds and hydrolyzes ATP to drive myosin motor
Myosin is divided into what?
Conventional or type two and unconventional
Primary function for conventional Myosins
Muscle contraction, can be used for cell splitting, generating tension, cell migration, or turning growth behaviour
Myosin 2 consists of: 
- Pair of globular heads that contain catalytic site
- Pair of necks, consisting of single alpha helix and two associated light chains
- Single, long, rod shaped tail formed by intertwining of long alpha helical sections of two heavy chains
Each muscle fibre contains what?
Hundreds of myofibrils
Each myofibril consists of what?
Repeating linear array of sarcomeres
A sarcomere extends from: 
One Z line to the next Z line
A sarcomere contains what?
Staining M line that lies in Centre of H zone
I band contains only (thick or thin) filaments?
Thin filaments
H band contains only (thick or thin) filaments?
Thick filaments
Sliding filament model of muscle contraction
- A band remains constant length
- H and I bands decrease in width then disappear
- Z lines move inward until they contact outer edges of A band
Thin filaments of a skeletal muscle contain what?
Actin, tropomyosin, troponin
What is tropomyosin?
Elongated molecule that fits securely into grooves within thin filament and is associated with seven actin subunits
What is troponin?
Globular protein complex composed of three subunits, a long thin filament contact both actin and tropomyosin
During a contraction each myosin head: 
Extends outward and binds tightly to a thin filament
So locomotion is needed for what?
- Tissue and organ development
- Formation of blood vessels
- Development of axons
- Wound healing
- Protection against infection
