cell adhesion 1

what is the definition of tissue?

the co-operative assembly of cells and extracellular matrix woven together to form a multicellular fabric with a distinctive function

what is the extracellular matrix?

matrix which gives supportive tissues their strength

what is the stress transmission mechanism in plants?

the extracellular matrix

what are the stress transmission mechanisms in animals?

the extracellular matrix
cytoskeleton and cell-cell adhesion that connect to the cytoskeleton of the neighbouring cells

what is the primary cell wall?

• in newly formed plants
• relatively thin and offers flexibility
• can expand as the cell grows

what is the secondary cell wall?

• once cell growth stops
• thicker and more rigid
• no longer needs to expand
• most common addition polymer is lignin

what is cellulose in cell walls?

• most abundant macromolecule on earth
• long unbranched chains of beta glucose subunits
• around 16 cellulose molecules form a microfibril
• mainly in secondary cell walls
• tensile strength similar to that of steel

how does pectin provide resistance to compressive forces?

• has long complex polysaccharides - rich in galacturonic acid
• highly hydrated so it binds cations - space filling effect
• resists compression
• crosslinks with cellulose to form the matrix
• abundant in primary cell walls

what is the primary cell wall made up of?

• cellulose microfibrils which provide tensile strength
• other polysaccharides crosslink cellulose microfibrils
• pectin provides resistance to compression
• middle lamella is rich in pectin and cements cell walls together

what is the structure of wood?

• cells have thick walls which remain when the cell dies
• forms long channels running vertically within the tree
• cell wall composed of lignin

what is lignin?

• complex polymer of cross linked phenolic compounds
• high wet strength

what are proteins in cell walls used for?

• used in remodelling during growth
• in contrast with animals which use more proteins

how does the orientation of cellulose microfibrils affect turgor pressure?

• cell wall helps to maintain internal pressure
• cellulose microfibrils resist stretching
• orientation of cellulose influences the direction in which cell elongates
• important during growth
• influences tissue shape

what is the deposition of cellulose?

• beneath the plasma membrane

what is cellulose synthesis?

• cellulose synthesis machinery is physically linked to underlying microtubules
  -microtubules act as tracks that guide enzyme complexes
• cytoskeleton indirectly controls the architecture of plant tissue

how are animal tissues made up?

• specialised connective tissue have abundant ECM
• ECM directly bears the mechanical stresses
• epithelial tissues have much less ECM
• cytoskeleton carries the mechanical load from cell to cell

what is the composition of the connective tissue - bone?

• bone forming cells (osteoblasts) secrete collagen matrix
• Ca2+

what are the features of the connective tissue - cartilage?

• present in many joints
• strong

what are the features of the connective tissue - vitreous humour?

• between lens and retina
• clear

what is the major protein of the ECM?

collagens

what are the features of collagen in the ECM?

• abundant in bone

how is a fibre of collagen formed?

monomer --> trimer --> fibril -- > fibre

what is a fibroblast?

a cell that secretes collagen and other fibres

what is the layout of collagen fibrils in the skin?

• arranged in a plywood pattern
• allows skin to resist tensile strength in multiple directions

what is the layout of collagen fibrils in tendons?

• tendons attach muscle to bone
• collagen fibres align in parallel along the axis of extension

how do fibroblasts influence the alignment of collagen fibres?

fibroblasts pull on and shape the collagen they have secreted

what are collagen precursors?

• collagen molecules secreted in a precursor form
• theres additional peptide extensions that obstruct premature fibril assembly
• collagen precursors are cleaved to form mature collagen outside the cell

what occurs when there is incorrect collagen assembly?

• can cause skin to become hyperextensible
• EDS are cause by mutations in genes encoding collagens and proteins that affect collagen assembly