Cytoskeleton and Cell Junctions
Page 2: Learning Outcomes
Explain the importance of the cytoskeleton in the cell.
Describe the molecular structure and function of:
Microtubules
Microfilaments
Intermediate filaments
Distinguish between these structural elements.
Describe the structure of centrioles in animal cells.
Explain centrioles' role in cell division and centrosome formation.
Show microtubular spindle fibres' origin from gamma-tubulin rings in the centrosome.
Discuss the significance of intercellular junctions and identify three main types.
Describe structure and function of:
Adhering junctions
Gap junctions
Tight junctions.
Page 3: Cytoskeleton Overview
The cytoskeleton is a three-dimensional network maintaining animal cell shape and organization.
Consists of tubular and filamentous structures.
Elements include:
Microtubules
Microfilaments
Intermediate filaments.
Page 4: Components of Cytoskeleton
Microtubules: Thick, rigid structures.
Microfilaments: Solid, thinner filaments.
Intermediate filaments: Vary in thickness and composition.
All components are formed from soluble protein pools in the cytoplasm.
Page 5: Size Comparison of Cytoskeletal Elements
Microtubules: ~25nm diameter.
Intermediate filaments: 10-12nm diameter.
Microfilaments: 5-7nm diameter.
Page 6: Microtubules - Structure
Hollow cylinders, 25-30nm in diameter.
Composed of 13 subunits forming a left-handed helix (heterodimer of alpha- and beta-tubulin).
Protofilaments are aligned parallel to the tubule's long axis and display both + and - ends.
Page 7: Microtubules - Function
Structural/support roles in cells:
Axoneme of cilia and flagella.
Centrioles' components.
Spindle fibres during cell division.
Support intracellular transport in axons of nerve cells.
Page 8: Microtubules in Cilia and Flagella
Ciliary structures can be motile (sperm and epithelial cells) or non-motile(Cilium Kidney), showing different arrangements of microtubule structures (9+2 for motile and 9+0 for non-motile).
Page 9: Microfilaments Overview
Also known as actin filaments.
Appear denser than microtubules under electron microscopy.
Essential for maintaining cell shape and contributing to motility.
Page 10: Microfilaments - Structure
Solid filaments, 5-7nm diameter, primarily composed of actin protein.
Mostly found in animals cells
Often found in networks or bundles beneath the plasma membrane, contributing to structures like intestinal microvilli.
Page 11: Size Comparison of Microfilaments
Microtubules: 25nm.
Microfilaments: 5-7nm.
Page 12: Intermediate Filaments - Structure
Heterogeneous in composition; consist of at least five main types based on proteins.
Size ranges from 7-11nm.
Include type 1&2 keratins (divided into acidic and basic), 3 vimentin-like proteins(cells of mesodermal origins), 4 neurofilaments( nerve axons), and 5 nuclear laminins(Nuclear lamina).
Page 13: Intermediate Filaments Composition
Structure consists of parallel dimers interacting to form coiled coils, providing mechanical support within cells.
non-alpha-helical (globular)surrounds the alpha helical rod.
Page 14: Intermediate Filaments Size
Solid filaments: 7-10nm in diameter.
Page 15: Centrioles Overview
Present in all animal cells, ciliated plant cells.
Located near the nucleus, often in association with the Golgi apparatus.
This area is known as the microtubule organizing center.
Page 16: Centrioles - Structure
Typically consist of two cylindrical structures oriented at right angles (9x3 structure of microtubules).
one pair per cell during interphase
Tublin
Page 17: Centrioles - Triplet Structure
Each triplet has a complete microtubule set (Set A) and two partial sets (Sets B and C).
Page 18: Centrioles - Cartwheel Structure
A specialized structure at one end, providing additional support and formation of centrioles.
Page 19: Centrioles - Function in Cell Division
Centrioles replicate prior to cell division and migrate to cell poles to form centrosomes.
forms areas known as centrosomes
Page 20: Centrosomes
Main microtubule organizing center of the cell.
Comprised of two orthogonally arranged centrioles and pericentriolar material.
material contains proteins responsible for microtubule nucleation and anchoring
Page 21: Microtubule Nucleation in Centrosomes
Microtubules arise from gamma-tubulin rings situated in the centrosomal matrix, serving as nucleation sites for one microtubule.
Page 22: Centrosomes and Spindle Fibres
Centrosomes initiate an aster of microtubules that form spindle fibres during cell division, which attach to chromosomes at the centromere.
Page 23: Types of Cell Junctions Overview
Common types: Tight junctions, adherens junctions, desmosomes, and gap junctions.
Page 24: Cell Junctions Significance
Most cells in tissues are linked together, fostering communication and structural integrity.
intercellular space is between 20-30nm wide
Page 25: Adhesion/Adhering Junctions
Mechanically strong junctions binding epithelial cells, featuring cadherins as transmembrane proteins.
Page 26: Cadherins
Link cytoplasmic structures to the cytoskeleton and are critical for cell adhesion; variations include E-cadherin, N-cadherin, and P-cadherin.
Page 27: Linking to Actin Microfilaments
Cadherins attach to actin via linker proteins, forming intercellular connections.
Page 28: Desmosomes Overview
Disc-like junctions that anchor cells together via intermediate filaments, involved in tissue resilience.
20nm thick
Spot desmosomes connect via intermediate fillaments
Hemi connect the basal surface
different integrens
Page 29: Desmosomes Structure
Comprising cadherins and intermediate filaments, desmosomes enhance cell adhesion strength.
Page 30: Hemidesmosomes
Connect basal epithelial cells to basal lamina using integrins for cell adhesion.
Page 31: Gap Junctions - Function
Facilitate intercellular communication by allowing ion and small molecule exchange, formed by connexins.
intercellular space is reduced 2-4nm
Page 32: Gap Junctions Structure
Composed of hexagonal arrays of connexin proteins forming a hydrophilic channel, crucial in cardiac muscle for electrical impulse transmission.
Page 33: Tight Junctions - Overview
Form close connections in epithelial cells, serving as barriers to prevent molecule passage through intercellular space.
Page 34: Tight Junctions - Structure and Function
Composed of strands of transmembrane proteins that create an impermeable barrier between cells to maintain concentration gradients.
Page 35: Summary Diagram of Junctions
Illustrates connections between tight junction proteins, intermediate filaments, and plasma membranes.
Page 36: Pemphigus Vulgaris
An autoimmune disease affecting desmosomes, leading to skin blistering due to disrupted cell adhesion.
autoantibodies target the proteins of the desmosomes leading to disruption of cells
pulling apart skin and pulls apart and allows abnormal movements
Notable health risks and potential mortality rate of 5-15%.