Epithelial Cells 1 Flashcards
Review Nucleus
The nuclear envelope is a double membrane.
Nucleolus - site of production of subunits of ribosome.
The subunits are made of ribosomal RNA and associated proteins
The nuclear envelope is continuous with the ER which is involved in packaging and processing proteins.
Nuclear pores are complexes, they are not just holes in the membrane.
Review Endoplasmic Reticulum
rER - exists as flattened sheets which is studded on its outer surface with ribosomes.
sER - more tubular and lacks ribosomes. It has a major function in lipid metabolism.
Review Golgi Apparatus
Stacked, membrane bound, flattened sacs involved in modifying, sorting, and packaging macromolecules for secretion or for delivery to other organelles.
Vesicles carry macromolecules from the Golgi apparatus to various destinations.
Describe Phagocytosis and Pinocytosis?
Phagocytosis - cell eating - internalisation of particles
Pinocytosis - cell drinking - extracellular fluid is internalised - major function: receptor mediated endocytosis
Review Mitochondria?
Mitochondria - Energy metabolism - production of ATP - the number of mitochondria you see in a cell is indicative of the cell’s metabolic activity.
Review Peroxisomes?
Peroxisomes - contain enzymes involved in lipid and oxygen metabolism e.g. catalases, peroxidases
Review Microtubules?
Polymers of a and b tubulin
~20nm in diameter
Involved in cell shape and act as tracks for the movement of organelles and cytoplasmic components within the cell.
Motor proteins are necessary for this movement.
It is a major component of cilia and flagella. The microtubules are arranged in a 9 and 2 formation when you take a cross section of a cilium
Radiate from the MTOC and are part of the spindle fibres in mitosis.
Review Intermediate Filaments?
rope-like filaments
Diameter - 10-15nm (Intermediate because their diameter is in between microtubules and microfilaments)
Different cell types have different intermediate filaments (e.g. epithelial cells - cytokeratin/mesenchymal cells - vimentin/neurons - neurofilament protein)
IFs give mechanical strength to the cells.
Desmosomes are connected by cytokeratins.
Nuclear Lamins - intermediate filaments which form a network on the internal surface of the nuclear envelope - they are involved in stabilising the envelope.
Review Microfilaments?
Polymers of actin associate with adhesion belts in epithelia and endothelia and with other plasma membrane proteins.
Involved in cell shape and cell movement (crawling and contractility)
Accessory proteins which associate with actin e.g. myosin
Monomer = Globular Actin (G-actin)
Microfilaments = Filamentous Actin (F-actin)
Usually bundled near the periphery of the cell.
Has a helical structure
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)
Define the ECM?
the insoluble material that you will find extracellularly (e.g collagen, elastin, proteoglycan)
ECM molecules tend to be fibrillar and form fibres which can form networks.
Describe Epithelial cells?
form layers - because they form stable cell-cell junctions - allows them to form cohesive layers.
Line body surfaces externally and internally
Involved in transport, absorption, secretion and protection
What are the two forms of Cell-Cell junction? What are the arrangement of Cell Junctions from apical to basal?
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.
What is the Zone Occludens?
Tight Junction.
The more elaborate the networks - the tighter the seal.
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.
What is the Zone Adherens?
Adhesion Belt = Zonula Adherens
Formed just basal to the apical tight junction.
Cadherins - bind to similar molecules on the adjacent cell and cluster (with the help of actin) to form these junctions.
The actin cytoskeleton is closely associated with these junctions.
When epithelial cells touch one another, the adherens junction is the first to form.
