Cytoskeleton and Its Functions

Primary Role

• Maintains Cell Shape: Essential for animal cells as they lack a cell wall.
• Supports Cell Structure: Provides mechanical strength.
• Facilitates Cell Movement and Transport:
  • Microtubules serve as tracks for vesicle movement.
  • Involved in Cell Division: Forms part of centrosomes, helps in chromosome movement.

Types of Cytoskeleton

Microtubules

• Thickest component of the cytoskeleton.
• Composition: Made of globular proteins called tubulins, specifically alpha and beta tubulin dimers.
• Functions:
  • Acts as tracks for motor proteins like dynein, reliant on ATP for movement.
  • Involved in flagellar and ciliary movement.
  • Essential in cell division for spindle formation.

Microfilaments (Actin Filaments)

• Thinnest component.
• Location and Function:
  • Found in muscle cells, essential for muscle contraction.
  • Involved in amoeba movement and cell division.
  • Composition: Made of actin subunits, also present in pseudopodia and cytoplasmic streaming.

Intermediate Filaments

• Intermediate diameter between microtubules and microfilaments.
• Structure: Made of fibrous proteins like keratins, more stable.
• Functions:
  • Anchors organelles, e.g., nucleus.
  • Provides structural support, forms nuclear lamina.
• Location: Strengthens nerve cell axons.

Motor Proteins and Movement

• Dynein and Kinesin: Motor proteins that help transport vesicles along microtubules.
• Energy Source: ATP.
• Vesicle Transport: Involves receptor proteins on vesicles, motor proteins attached to microtubules.

Cell Structures Involving Cytoskeleton

Centrosomes and Centrioles

• Centrosome: Microtubule organizing center near nucleus.
• Centrioles: Composed of nine triplets of microtubules.
• Role in Cell Division: Duplication necessary before cell division.

Cilia and Flagella

• Structure: Composed of microtubules in a 9+2 arrangement.
• Basal Body: Anchors cilia/flagella, similar to centriole structure.
• Function: Enables movement of cells or fluid over cell surface.

Plant and Animal Cell Structures

Extracellular Matrix (ECM)

• Animal Cells: Composed of collagen, proteoglycans, and fibronectin.
• Role: Provides structural support; integral in cellular signaling.

Cell Walls

• Plant Cells: Composed of cellulose, provides rigidity and protection.

Cell Junctions

• Animal Cells:
  • Tight Junctions: Prevent leakage of extracellular fluid.
  • Desmosomes: Anchor cells into strong sheets.
  • Gap Junctions: Allow ion and small molecule passage.
• Plant Cells:
  • Plasmodesmata: Channels allowing transport between cells.

Tissue Types in Multicellular Organisms

Animal Tissues

• Epithelial: Covers body surfaces; types include squamous, columnar, cuboidal.
• Connective: Supports other tissues; types include bone, blood, cartilage.
• Muscle: Skeletal, cardiac, smooth muscle, responsible for movement.
• Nervous: Composed of neurons and glial cells, transmits signals.

Plant Tissues

• Dermal: Protective covering.
• Vascular: Transports water, nutrients; composed of xylem and phloem.
• Ground: Provides support and storage, includes parenchyma, collenchyma, and sclerenchyma.