1 Epithelial Cells Flashcards
Q: What is the structure of the nucleus? Pores?
A: The nuclear envelope is a double membrane -> The nuclear envelope is continuous with the ER
Nuclear pores are complexes, they are not just holes in the membrane
Q: What are the 2 types of ER? Role?
A: rER - exists as flattened sheets which is studded on its outer surface with ribosomes-> membrane protein synthesis/ those that need to be exocytosed
sER - more tubular and lacks ribosomes. It has a major function in lipid metabolism + detoxification // also site of Ca 2+ storage
Q: What is the nucleolus made of? Function? Contains?
A: nucleolus = aggregate of the clusters of rRNA genes
Nucleolus - site of production of subunits of ribosome
also contains the synthesised rRNA + proteins being assembled to make ribosome units
Q: Why are there many copies of rRNA genes required?
A: need many to reach demands of cells (since each one can only produce one rRNA at a time)
Q: What are ribosomes made of? Where do they reside? (2) Difference?
A: made of 2 distinct subunits each contains ribosomal RNA and a protein
can be free in cytoplasm- make cytoplasmic proteins
or attached to rER/outer membrane of nucleus- make membrane proteins and proteins to be packaged in membranous organelles
Q: What is the role of ribosomes?
A: organelles that read messenger RNA mRNA to synthesise polypeptide chains
Q: What is a nuclear pore? Role?
A: protein complex- large pores contain elaborate arrangements of associated proteins
control import and export of macromolecules into and out of the nucleus
Q: What is the relationship between the nuclear envelope and the ER?
A: physical continuity
Q: What is the nuclear lamina? Importance? Targeted when and why?
A: specialised type of cytoskeleton (intermediate filaments) formed on the internal surface of the nuclear envelope
important in controlling the assembly/dissembly of the nuclear envelope in cell division
during cell division - when targeted-> modified and allowed breakdown of nuclear membrane (fragments reassemble after cell division)
Q: Describe the Golgi apparatus structure. Function? Direction?
A: Stacked, membrane bound, flattened sacs involved in modifying, sorting, and packaging macromolecules for secretion or for delivery to other organelles
cis side is alligned to ER and trans to cell periphery -> allows GA to receive vesicles from ER and direct them to rest of cell and cell surface
Q: Describe mitochondrion role. Number in a cell indicative of? Structure?
A: Energy metabolism - production of ATP - the number of mitochondria you see in a cell is indicative of the cell’s metabolic activity
cristae
mito matrix
intermembrane space
Q: What are peroxisomes? Importance?
A: enclosed in single membrane
contain enzymes involved in lipid and oxygen metabolism e.g. catalases, peroxidases
in oxidation reactions
Q: What is phagocytosis?
A: cell eating - internalisation of particles
Q: What is pinocytosis?
A: cell drinking - extracellular fluid is internalised - major function: receptor mediated endocytosis
*Q: What is the cytoskeleton? Why described as dynamic?
A: A system of 3 types of filaments formed by the polymerisation of protein monomers
microfilaments
intermediate filaments
microtubules
Dynamic =The cytoskeleton is NOT FIXED. The various elements of the cytoskeleton are subject to rapid remodelling by a variety of biochemical and bio-mechanical signals
*Q: Describe microfilaments. Monomer? Structure? Role? Which accessory proteins associate with it? Usually bundled where?
A: Monomer = Globular Actin (G-actin)
Polymers of actin associate with adhesion belts in epithelia and endothelia and with other plasma membrane proteins -> helical structure
Involved in cell shape and cell movement (crawling and contractility)
Accessory proteins which associate with actin =myosin
Usually bundled near the periphery of the cell
*Q: Describe intermediate filaments. Monomer? Diameter? Role?
A: A group of polymers of filamentous proteins which form rope-like filaments
Diameter - 10-15nm
give mechanical strength to the cells
*Q: Describe microtubules. Monomer? Diameter? Role? Radiate out from?
A: 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.
Typically, microtubules tend to radiate out from a particular point within a cell.
That point is called the Microtubule Organising Centre (MTOC).
*Q: Which cytoskeleton component is part of spindle fibres in mitosis?
A: Microtubules
*Q: Which cytoskeleton component is the major structural component of cilia and flagellae?
A: Microtubules
9 and 2 formation in both
*Q: What are the main cell types? (5)
A: 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)
contractile tissues- skeletal muscle, cardiac muscle, smooth muscle
*Q: Give examples of how tumours retain characteristics of the cell type from which they originated? (4)
A: Epithelial Cancers = Carcinoma
Mesenchymal Cancers = Sarcomas
Haematopoietic Cancers = Leukaemias (bone marrow cells) + Lymphomas (lymphocytes)
Neural Cancers = Neuroblastomas (neurones) + Gliomas (glial cells)
*Q: Describe ‘tissue’. Made of?
A: a group of cells whose type, organisation and architecture are integral to its function
Tissue = Cells + Extracellular Matrix + Fluid
*Q: What is the extracellular matrix? Definition. Generally composed of? What is the organisation?
A: Definition - the insoluble material that you will find extracellularly
generally composed of fibrillar (or reticular) proteins (e.g collagen, elastin) embedded in a hydrated gel (proteoglycans or ‘ground substance’).
may be poorly organised (eg loose connective tissue) or highly organised (tendons and bone and basal lamina)
*Q: What is the organisation of epithelium? Line? What’s their function? What’s key to maintenance and formation?
A: 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
cell-cell junctions
*Q: What do cell-cell junctions allow to form? Found?
A: Continuous epithelial layers can form because cells make stable cell-cell junctions
in many epithelia, the cell-cell junctions are found in the apical region of cell-cell contact as a junctional complex
*Q: What are the 2 forms of cell-cell junctions in epithelia?
A: Zonulae (belts) and Maculae (spots)
*Q: Describe the junctional complex arrangement in epithelial tissue. Another important junction?
A: typically arranged:
tight junction nearest the apex
adhesion belt
desmosomes= scattered throughout the lateral membrane (spot adhering junctions)
gap junctions- act as regions of direct communication between adjacent cells
*Q: Describe tight junctions. Another name?
A: Zonula Occludens (occluding junction)
points on adjacent membranes form close contacts at apical lateral membranes
form a network of contacts, the more elaborate the network, the tighter the seal
act to seal paracellular pathways (ie between cells)
segregates apical and basolateral membrane polarity
*Q: Describe the adhesion belt. Another name? Formed where? What helps them form? What’s closely associated with it?
A: Zonula Adherens
Formed just basal to the apical tight junction.
transmembrane adhesion molecule = 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.
controls the formation of other junctions (once it forms itself) hence it is the Master Junction
*Q: Describe demosomes. Another name? Found where? What helps adhesion? Linked to? Provides?
A: desmosomes = 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
provides good mechanical continuity between cells
*Q: Describe gap junctions. Another name? Made of? Allow passage of? What can control? Also known as? esp important in which cells?
A: macula communicans (spot junction)
Made up of clusters of pores which are formed of
6 identical subunits in the membrane
pores are continuous with pores on adjacent membranes
Allow the passage of ions and small molecules between cells- direct cell communication
pH, Ca 2+ conc, voltagea and some signally molecules can affect passage ie open and close pores thereby controlling intercellular communication
also known as the electrical synapse- important in the passage of electrical signals in some tissues (can conduct signal between cells esp important in cardiac cells)
*Q: Describe (chemical) synapses. Found mainly in? Formed where? Information passed?
A: Found in neural tissue - not epithelial
button like junctions formed between neurones or their targets eg muscle
Pass information in one direction (chemical signalling system)
Q: What is heterochromatin?
A: regions of condensed DNA (less active)
Q: What are cisternae?
A: flattened sacs of membrane of the endoplasmic reticulum (and GA)
Q: Cells with lots of sER?
A: high steroid production usually
*Q: What is the arrangement of microtubules?
A: 9 mt doublets and 2 central mt make up core of cilia and flagellae: 9+2 arrangement
*Q: What are cell-cell junctions capable of? Controlled by?
A: changing their assembly and organisation (laible)
dynamic assembly and disassembly = controlled by variety of factors in health and disease
Q: Approximately how many cell types are there in the human body?
A: 200
*Q: Demonstrate the following on a suitable transmission
electron micrograph: nucleus; nucleolus; nuclear
envelope; mitochondrion; rough endoplasmic reticulum;
smooth endoplasmic reticulum; ribosomes; Golgi
apparatus; secretory granule; plasma membrane;
cytoskeletal components.
A: REFER
*Q: What is a brush border?
A: microvilli-covered surface of simple cuboidal epithelium and simple columnar epithelium cells
*Q: What is cilia? role? (2)
A: short microscopic hair-like vibrating structure found in large numbers on the surface of certain cells, either causing currents in the surrounding fluid, or, in some protozoans and other small organisms, providing propulsion
*Q: features of epithelial cells: apical surface; basolateral surface; brush border; microvilli; cilia; cell junction; basal lamina (basement membrane). Demonstrate them on suitable transmission electron micrographs.
A: REFER
