1. Epithelial cells Flashcards
Where are ribosomes found and what do they do there?
Free in cytoplasm: synthesise cytoplasmic proteins
OR
Attached to outer membrane of nuclear envelope and ER: make membrane proteins and proteins to be packaged in membranous organelles.
What is the function of nuclear pores?
control import and export of macromolecules into and out of nucleus
What is the relationship between nuclear envelope and endoplasmic reticulum?
There is physical continuity between nuclear envelope and ER
Describe the rough endoplasmic reticulum
Stacks of flattened membrane leaflets (cisternae), studded on outer face with ribosomes
What is the RER the site of?
protein synthesis and packaging in membrane-bound structures, e.g. secretory vesicles, lysosomes
What is the function of the smooth endoplasmic reticulum?
Detoxification
Lipid metabolism
Enzymes involved are typically associated with the membranes.
Site of Ca2+ storage in cells (important in cell-signalling)
What is the Golgi apparatus and what does it do?
System of stacked, membrane bound, flattened sacs
Modifies, sorts and packages macromolecules for secretion/ delivery to other organelles
How is are the faces of the Golgi apparatus aligned?
Cis: to ER
Trans: to cell periphery
What are peroxisomes?
Single membrane bound organelles
Contain enzymes involved in lipid and oxygen metabolism, e.g. oxidases, catalases, peroxidases
What is the cytoskeleton?
A system of filaments formed by the polymerisation of protein monomers
What 3 types of filament constitute the cytoskeleton?
Microtubules
Intermediate Filaments
Microfilaments
What are microtubules made of and what is the diameter of a microtubule?
Polymers of alpha and beta tubulin heterodimers
20nm thick
What are microtubules used for?
Movement of organelles through the cell
Involve motor proteins
Involved in spindle fibre formation
What are microtubules major components of?
Cilia and flagellae
Form 9 + 2 arrangement in the core
(9 doublets + 2 central singlets)
Describe the organisation of microtubules in cells.
Originate from a point within the cell called the microtubule organising centre (MTOC)
Describe structure of intermediate filaments
Group of polymers of filamentous proteins
Form rope-like filaments
10-15nm diameter
Which component of the cytoskeleton distinguishes different cell types?
Intermediate Filaments are different for different cell types
What is the function of intermediate filaments?
Give mechanical strength to cells
What are desmosome cell-cell adhesions connected by?
Intermediate Filaments
Where else are intermediate filaments found other than in the cytoplasm?
Nuclear lamins are IF’s found on the internal surface of the nuclear envelope
Provide support
What are microfilaments made of and what is their diameter?
Polymers of Actin (filamentous actin, F-actin)
5-9nm diameter
What do microfilaments associate with?
Adhesion belts in epithelia and endothelia
What are microfilaments involved in?
cell shape and movement
major component of contractile apparatus of muscle and involved in contraction of non muscle cells
What is the monomer of microfilaments?
G-actin (globular actin)
How is the cytoskeleton dynamic?
Various elements are subject to rapid re-modelling, stimulated by biochemical and bio-mechanical signals.
What are the 5 major groups of cell type?
Connective tissue Contractile tissue Haematopoietic Neural Epithelial
Give 3 examples of connective tissue cells
Fibroblasts
Chrondocytes
Osteocytes
Give 3 examples of contractile tissue cells
Skeletal muscle
Cardiac muscle
Smooth muscle
Give 3 examples of haematopoietic cells
Blood cells
Tissue-resident immune cells
Cells of the bone marrow from which they’re derived
Give 2 examples of neural cells
Neurones
Glial cells
What are epithelial cells?
Cells forming continuous layers, these layers line surfaces and separate tissue compartments and have various other functions
What do tumours retain?
Characteristics of the cell type from which they originate
e.g.
epithelial cancers= carcinomas
neural cell cancers= neuroblastomas
What is a tissue?
A group(s) of cells whose type, organisation and architecture are integral to its function Composed of cells, extracellular matrix and fluid
Define ‘Extracellular Matrix’.
The insoluble material deposited by cells found extracellularly.
Composed of fibrillar/ reticular proteins embedded in hydrated gel
Epithelial organisation
Epithelial cells make organised, stable cell-cell junctions to form continuous, cohesive layers
Epithelial layers line internal and external body surfaces
List 4 functions of epithelial layers
Transport
Absorption
Secretion
Protection
What are key to the formation and maintenance of epithelial layers and why?
Cell-cell junctions
Give epithelia mechanical integrity and act to seal intercellular pathway of layer
What are the 2 forms cell-cell junctions generally found in?
Zonulae (Belts)
Maculae (Spots)
How are cell-cell junctions typically arranged in epithelia?
Apical junctional complex containing a tight junction nearest the apex
Then an adhesion belt
Then scattered throughout the lateral membrane, desmosomes (spot adhering junctions)
What are the 4 main types of cell-cell junctions (in order of apical to basal)?
Tight
Adhesion belt
Desmosomes/Gap Junctions
What is the role of tight junctions?
Seals off the paracellular pathways
Allows polarity
Stops proteins that diffuse through membranes.
Describe tight junctions
Zonula occludens (Belt) Points on adjacent membranes form close contacts at apical lateral membranes The more elaborate the network of contacts the tighter the seal
Describe the structure and function of the adhesion belt.
Zonula adherens (belt)
Usually formed just basal to apical TJ
Controls assembly of other junctions
What are transmembrane adhesion molecules?
Cadherins
Family of Ca 2+ dependent cell adhesion molecule s
What do cadherins associate with?
Actin
Describe the structure and function of desmosomes.
Macula adherens (spot) Found at multiple spots between adjacent cell membranes Involves cadherins interacting to maintain adhesion. Provide good mechanical continuity between cells
What are desmosomes linked to?
Intermediate filament cytoskeleton
Describe the structure of gap junctions
Macula communicans (spot) Made of clusters of pores formed from 6 identical subunits in the membrane (pores continuous with pores in adjacent cell membrane)
What is the role of Gap junctions?
Allows transport of ions and small molecules between cells
What can open/ close pores in gap junctions thereby controlling intercellular communication?
pH
Ca 2+ conc
Voltage
Some signalling molecules
What are gap junctions also known as?
Electrical synapse
Important in passage of electrical signals in some tissues
Chemical synapse
Communicating junction
Mainly in neural tissue
Information passed 1-way via chemical signalling
Why are cell-cel junctions described as labile?
They’re capable of changing their assembly and organisation
