Tissues 1- Epithelial Cells Flashcards
3 types of filaments in cytoskeleton
Microtubules
Intermediate filaments
Micro filaments
Describe the composition, roles (4) and the arrangement in the cell of microtubules
Composition:
Polymers of a and b tubulin
~20nm in diameter
Role:
Involved in cell shape
act as tracks for the movement of organelles and cytoplasmic components within the cell. Motor proteins are necessary for this movement.
Microtubules are the major structural component of cilia and flagellae.
Microtubules are part of the spindle fibres involved in mitosis.
Arrangement in cell
Typically, microtubules tend to radiate out from a particular point called the Microtubule Organising Centre (MTOC).
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What is the structure (2) and role of intermediate filaments
Also what are nuclear lamins?
Structure
A group of polymers of filamentous proteins which form rope-like filaments
Diameter - 10-15nm
IFs give mechanical strength to the cells.
Nuclear Lamins - intermediate filaments which form a network on the internal surface of the nuclear envelope - they are involved in stabilising the envelope.
Describe the structure (3), role (3) and cell location of microfilaments
Structure:
Polymers of globular actin
Has a helical structure
5-9 nm
Role:
Involved in cell shape and cell movement (crawling and contractility)
Accessory proteins which associate with actin e.g. myosin
associate with adhesion belts in epithelia and endothelia and with other plasma membrane proteins.
Location
Usually bundled near the periphery of the cell.
4 Main cell types
Epithelial Cells - cells forming continuous layers - the layers line surfaces and separate tissue compartments.
Mesenchymal Cells - connective tissue - e.g. fibroblasts, chondrocytes, osteocytes, muscle cells
Haematopoietic Cells - blood cells and cells of the bone marrow from which they are derived
Neural Cells - nervous system - 2 main types: neurones (carry electrical signals) and glial cells (support cells)
What is the extracellular matrix
Definition - the insoluble material that you will find extracellularly (e.g collagen, elastin, proteoglycan)
ECM molecules tend to be fibrillar and form fibres.
These fibres can form networks (described as reticular).
They are often embedded in large ECM molecules which are very hydrated and form gel like structures like proteoglycans.
What type of cells form cell junctions?
Where are cell junctions found?
What are the 2 forms of cell junctions?
Continuous epithelial layers can form because cells make stable cell-cell junctions.
The cell-cell junctions are found in the apical region of cell-cell contact as a junctional complex.
Two Forms of Cell-Cell Junction: Zonulae (belts) and Maculae (spots)
Arrangement of Junction: Apical —> Basal
Tight Junction
Adhesion Belt
Desmosomes and Gap Junctions
Gap Junctions - main function isn’t to hold the cells together or to seal the spaces between the cells but actually to communicate between the cells.
Describe tight junctions
What is the role of tight junctions
What are the kiss points?
Tight Junction - it is a belt junction because it is a zonula
Role:
These contacts are in the form of a network - they seal the paracellular pathway.
The tight junctions also segregate membranes - they stop proteins which diffuse through membranes - allows adjacent cells to be different and allows polarity to be established.
The kiss points are a linear array which form a network of integral membrane proteins that hook up with membrane proteins on adjacent cells.
Describe adhesion belts
What are cadherins
Adhesion Belt = Zonula Adherens
Cadherins - bind to similar molecules on the adjacent cell and cluster with the help of actin to form these junctions.
When epithelial cells touch one another, the adherens junction is the first to form.
After the adherens junction has formed, other junctions can begin to form - hence it is the Master Junction.
Describe Desmosomes
Where are they found?
How do they work
Macula Adherens - SPOT junction
They are dotted around the lateral membrane between cells
They have cadherin-like-molecules which are involved in transmembrane cell adhesion
Desmosomal Cadherins link to the intermediate filament cytoskeleton which is cytokeratin in epithelium.
What are gap junctions made up of?
What is their role? (2)
Made up of clusters of pores which are formed by membrane proteins.
Role:
Allow the passage of ions and small molecules between cells. -Only relatively small molecules and ions can get through.
They can open and close the pores - can be controlled by: electrical activity, calcium concentration
