BIO 253 Cytoplasm

T Cell: A type of lymphocyte involved in immune response.
Nanotube: A cylindrical nanostructure, potentially in biomedical applications.
Cancer Cell: Abnormal cells that divide uncontrollably.
Cytoskeleton: A network of fibers that helps maintain cell shape and aids in cell movement and division.
Size of Nanotube: 4 μm indicates the diameter or length of these structures.

Microtubules (Tubulins)
- Composed of tubulin protein, they serve various functions including supporting cell shape, enabling transport within cells, and facilitating cell division.
Intermediate Filaments
- Made of various proteins, they provide mechanical support to the cell.
Microfilaments (Actins)
- Primarily made of actin, they are involved in cell motility and shape.

Definition: Definitions of Intermediate Filaments effectively contribute to cellular structure and strength.
Components: Various proteins contribute, including keratin (found in skin and epithelia).
- Size: Typically about 46 nm.
- Structure: Composed of monomers forming dimers, which then assemble into antiparallel tetramers—creating protofilaments and protofibrils.
- Functional Attributes: Stretch-resistant and provides tensile strength, important for cell junctions.

Keratin: Found in skin and other epithelial cells, provides strength and durability.
Vimentin: Found in connective tissues and smooth muscles, supports cell shape and integrity.
Nuclear Lamins: Structurally support the nuclear envelope in eukaryotic cells, forming the nuclear lamina which provides mechanical support.

Structure and Assembly:
- Key components are $ ext{α-tubulin}$ and $ ext{β-tubulin}$ dimers that polymerize to form microtubules.
- Assembly occurs at nucleation sites leading to elongation of protofilaments, which combine to form microtubules.

Transition States: Microtubules undergo phases of polymerization and depolymerization (dynamic instability), crucial for cellular functions such as transport and mitosis.
- Growing Microtubule: Characterized by high levels of $ ext{GTP-tubulin}$.
- Shrinking Microtubule: Involves depolymerization and transformation of $ ext{GTP-tubulin}$ into $ ext{GDP-tubulin}$.
- Catastrophe and Rescue: Events signifying sudden transitions from growth to rapid shrinkage and potential recovery phases.
Capping Proteins: Stabilize and regulate the ends of microtubules, influencing dynamics significantly.

Structure: Composed of actin monomers that polymerize to form filamentous structures, providing shape and mechanical support.
Cell Motility: Actin polymerization drives protrusions like lamellipodia, contributing to cell movement.

Mechanics of Movement: Involves myosin pulling along actin fibers during muscle contraction; ATP hydrolysis provides the energy.

Key Player in Cytokinesis: Actin forms a contractile ring that mediates cell division.

Structure of Skeletal Muscle: Comprises fibers (cells) organized into bundles called fascicles, with actin and myosin filaments establishing the contractile units (sarcomeres).
Myosin/ATP Cycle: Myosin heads hydrolyze ATP to move along actin filaments, enabling muscle contraction.
- Steps of cycle: ATP detaching myosin, followed by binding, power stroke occurs as ADP and phosphate (Pi) are released.
- Calcium ions control the activity by altering actin-myosin interaction through troponin and tropomyosin regulation of binding sites.

Structure and Support: Cytoskeletal networks support cell shape and organization.
Intracellular Transport: Motor proteins like kinesin and dynein facilitate cargo movement along microtubules.
Contractility and Motility: Actin filaments enable cell shape changes essential for movement.
Spatial Organization: Maintains proper distribution of organelles and proteins within the cell.