1 Epithelial Cells

Question 1

Q: What is the structure of the nucleus? Pores?

Answer 1

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

Question 2

Q: What are the 2 types of ER? Role?

Answer 2

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

Question 3

Q: What is the nucleolus made of? Function? Contains?

Answer 3

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

Question 4

Q: Why are there many copies of rRNA genes required?

Answer 4

A: need many to reach demands of cells (since each one can only produce one rRNA at a time)

Question 5

Q: What are ribosomes made of? Where do they reside? (2) Difference?

Answer 5

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

Question 6

Q: What is the role of ribosomes?

Answer 6

A: organelles that read messenger RNA mRNA to synthesise polypeptide chains

Question 7

Q: What is a nuclear pore? Role?

Answer 7

A: protein complex- large pores contain elaborate arrangements of associated proteins

control import and export of macromolecules into and out of the nucleus

Question 8

Q: What is the relationship between the nuclear envelope and the ER?

Answer 8

A: physical continuity

Question 9

Q: What is the nuclear lamina? Importance? Targeted when and why?

Answer 9

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)

Question 10

Q: Describe the Golgi apparatus structure. Function? Direction?

Answer 10

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

Question 11

Q: Describe mitochondrion role. Number in a cell indicative of? Structure?

Answer 11

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

Question 12

Q: What are peroxisomes? Importance?

Answer 12

A: enclosed in single membrane

contain enzymes involved in lipid and oxygen metabolism e.g. catalases, peroxidases

in oxidation reactions

Question 13

Q: What is phagocytosis?

Answer 13

A: cell eating - internalisation of particles

Question 14

Q: What is pinocytosis?

Answer 14

A: cell drinking - extracellular fluid is internalised - major function: receptor mediated endocytosis

Question 15

*Q: What is the cytoskeleton? Why described as dynamic?

Answer 15

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

Question 16

*Q: Describe microfilaments. Monomer? Structure? Role? Which accessory proteins associate with it? Usually bundled where?

Answer 16

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

Question 17

*Q: Describe intermediate filaments. Monomer? Diameter? Role?

Answer 17

A: A group of polymers of filamentous proteins which form rope-like filaments

Diameter - 10-15nm

give mechanical strength to the cells

Question 18

*Q: Describe microtubules. Monomer? Diameter? Role? Radiate out from?

Answer 18

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).

Question 19

*Q: Which cytoskeleton component is part of spindle fibres in mitosis?

Answer 19

A: Microtubules

Question 20

*Q: Which cytoskeleton component is the major structural component of cilia and flagellae?

Answer 20

A: Microtubules

9 and 2 formation in both

Question 21

*Q: What are the main cell types? (5)

Answer 21

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

Question 22

*Q: Give examples of how tumours retain characteristics of the cell type from which they originated? (4)

Answer 22

A: Epithelial Cancers = Carcinoma

Mesenchymal Cancers = Sarcomas

Haematopoietic Cancers = Leukaemias (bone marrow cells) + Lymphomas (lymphocytes)

Neural Cancers = Neuroblastomas (neurones) + Gliomas (glial cells)

Question 23

*Q: Describe ‘tissue’. Made of?

Answer 23

A: a group of cells whose type, organisation and architecture are integral to its function

Tissue = Cells + Extracellular Matrix + Fluid

Question 24

*Q: What is the extracellular matrix? Definition. Generally composed of? What is the organisation?

Answer 24

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)

Question 25

*Q: What is the organisation of epithelium? Line? What's their function? What's key to maintenance and formation?

Answer 25

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

Question 26

*Q: What do cell-cell junctions allow to form? Found?

Answer 26

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

Question 27

*Q: What are the 2 forms of cell-cell junctions in epithelia?

Answer 27

A: Zonulae (belts) and Maculae (spots)

Question 28

*Q: Describe the junctional complex arrangement in epithelial tissue. Another important junction?

Answer 28

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

Question 29

*Q: Describe tight junctions. Another name?

Answer 29

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

Question 30

*Q: Describe the adhesion belt. Another name? Formed where? What helps them form? What's closely associated with it?

Answer 30

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

Question 31

*Q: Describe demosomes. Another name? Found where? What helps adhesion? Linked to? Provides?

Answer 31

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

Question 32

*Q: Describe gap junctions. Another name? Made of? Allow passage of? What can control? Also known as? esp important in which cells?

Answer 32

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)

Question 33

*Q: Describe (chemical) synapses. Found mainly in? Formed where? Information passed?

Answer 33

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)

Question 34

Q: What is heterochromatin?

Answer 34

A: regions of condensed DNA (less active)

Question 35

Q: What are cisternae?

Answer 35

A: flattened sacs of membrane of the endoplasmic reticulum (and GA)

Question 36

Q: Cells with lots of sER?

Answer 36

A: high steroid production usually

Question 37

*Q: What is the arrangement of microtubules?

Answer 37

A: 9 mt doublets and 2 central mt make up core of cilia and flagellae: 9+2 arrangement

Question 38

*Q: What are cell-cell junctions capable of? Controlled by?

Answer 38

A: changing their assembly and organisation (laible) dynamic assembly and disassembly = controlled by variety of factors in health and disease

Question 39

Q: Approximately how many cell types are there in the human body?

Answer 39

A: 200

Question 40

*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.

Answer 40

A: REFER

Question 41

*Q: What is a brush border?

Answer 41

A: microvilli-covered surface of simple cuboidal epithelium and simple columnar epithelium cells

Question 42

*Q: What is cilia? role? (2)

Answer 42

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

Question 43

*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.

Answer 43

A: REFER