Cell Adhesion 1 - intro lecture Flashcards
(38 cards)
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
