Cell Adhesion 1 - intro lecture Flashcards
what is the definition of a tissue?
a cooperative assembly of cells and extracellular matrix woven together to form a multicellular matrix woven together to form a multicellular fabric with a distinctive function
what is the cell theory and who proposed it?
- cells are the building blocks of life
- Schleiden and Schwann 1839
Explain stress transmission in multicellular organisms
- to make large and stable structures they need a way to transmit physical stress.
- two strategies of doing this
- Extracellular matrix (ECM) - plant and animal cells
- Cytoskeleton and cell-cell adhesions that connect the cytoskeletons of neighbouring cells - animal cells
Explain the primary cell wall in plant cells
- thin and flexible so they can expand as the cell growth
- middle lamella - has a lot of pectin. Cements cell walls of adjacent cells
- cellulose microfibrils - tensile strength
- pectin - fill spaces between cellulose, resistance to compression
- crosslinking polysaccharides - crosslink the cellulose microfibrils
What is the primary growing force of the plant cell?
Turgor pressure
What causes the secondary cell wall to form?
- cells have stopped growing
How does the secondary cell wall form?
- making the primary cell wall thicker or making a new one with a different composition
What is the most abundant macromolecule?
cellulose
What is the role of cellulose microfibrils in plant cell walls?
- give the cell wall tensile strength
What is a cellulose microfibril made from?
- 18 cellulose molecules connected by hydrogen bonds
What is a cellulose molecule made from?
- unbranched chains of glucose
- each glucose is alternatively inverted - neighbours are always in different orientations
- beta 1- 4 glycosidic bond
explain the structure of pectin
- alpha 1 - 4 glycosidic linkage between D-galacturonic acid units
explain the function of pectin in plant cell walls
- hydrated and binds cations
- space filling similar to glycosaminoglycans in animal ECM
- resists compression
- crosslinks with cellulose to form a matrix
- common in primary cell walls
Explain the structure of wood
- when a cell dies its wall stays, forming the channels
- contains lots of lignin which has a high strength when wet
What is the structure of lignin
A complex polymer of cross linked phenolic compounds
Explain the general structure of plant cell walls
- main structural components - polysaccharides (made from CO2 and H2O)
- some proteins for remodelling during growth, not as much as animals
Explain the orientation of cellulose microfibrils in plant cell walls
- horizontal - cell is more likely to grow in girth
- vertical - cell is more likely to grow in length
Cells elongate perpendicular to cellulose microfibrile orientation
Explain cellulose synthesis
- under the plasma membrane there are microtubules aligned with cellulose microfibrils
- microtubules help direct cellulose
- cellulose synthase complex connected to microtubules underneath
- microtubules guide enzyme complexes, determining the direction that cellulose is synthesised in (vertical or horizontal)
What is the ECM?
- extracellular matrix
- proteins and other molecules outwith the cell that give the cell support
Describe the structure of connective tissue
- lots of ECM - bears mechanical stress
Describe the structure of epithelial tissue
- less ECM - cytoskeleton carries mechanical stress
Give 5 places you would find connective tissues
- bone
- cartilage
- tendon
- skin
- vitreous humour
Describe the structure of bone
- osteoblasts (bone forming cells) secrete collagen matrix
- Ca, Mg and phosphate ions join matrix - forms hydroxyapitite
- hydroxyapitite - hard but not brittle so still flexible
- Osteons - concentric rings around central canal containing blood vessels and nerves
- bone doesn’t have much cells
Explain the structure of cartilage
- strong and flexible
- absorbs impact without breaking
- lots of ECM (collagen and proteoglycan (chondroitin sulphate)
- no mineralisation
Explain the structure of the vitreous humour
- in lens and retina
- clear viscous gel made of water, collagen and hyaluronic acid
- basically no cells
- doesn’t appear in tissue sections and H&E
Explain the structure of collagen
- tripple strand helix of collagen strands- long and stiff
Explain the structure of collagen fibrils
- triple collagen molecules that have assembled together to form
What are some different forms of collagen?
- triple woven
- fibrils
- fibers
- sit on surface of fibrils and hold them together and connect them to other components of the ECM
What is a collagen fibre?
- collagen fibrils which have joined together to form fibres
Where is collagen most common?
- bone
- tendon
- skin
What produces collagen?
fibroblasts
Explain the collagen fibril arrangement in skin
- plywood pattern
- allows skin to resist tensile stress in many directions
Explain collagen fibril arrangement in tendons
- tendons attach muscle to bone
- collagen fibres arrange parallel along the axis of tendon extension
What are fibroblasts?
cells that form collagen
how do fibroblasts work?
- produce and shape collagen
- if there is a gap between tissues, fibroblasts will connect it by controlling the formation of collagen
- useful in healing woulds and in the formation of tendons
What is the effect of incorrect collagen assembly?
- cause skin to be hypterextensible
- Ehlers-Danlos syndrome (EDS) is caused by mutation in genes that code for collagen and proteins involved in collagen assembly
Explain collagen precursors
- collagen secreted in precursor form
- peptide extensions to stop premature fibril assembly
- precursors cleaved by pro collagen protease to form mature collagen outside of the cel
- secreted by exocytosis where they then form large aggregates, would be harmful inside the cell
What is the role of procollagen protease?
cleave collagen precursors to form mature collagen outside of the cell
