Cell Adhesion 1 new

what is a tissue?

a cooperative assembly of cells and extracellular matrix (ECM) woven together to form a multicellular fabric with a distinctive function

what is the extracellular matrix?

a network of macromolecules that provides structural and biochemical support to the surrounding cells

how is mechanical stress transmitted in plants?

through the ECM

how is stress transmitted in animals?

through the ECM and the cytoskeleton connections between neighbouring cells by adhesion junctions

how are plant tissues strengthened?

by the cell wall

what is the function of the cell wall?

to provides structural support, determine cell shape and resist osmotic pressure

what are the 2 types of cell wall?

primary and secondary

what is a primary cell wall?

thin, flexible, present in newly formed cells, contains pectin allows expanion duriing growth

what is the secondary cell wall?

a thicker more rigid wall that forms after cell growth stops.

it contains lignin and provides mechanical strenght

what is lignin and what does it do?

a complex polymer of crosslinked phenolic compounds which adds rigidity and waterproofic to the secondary cell wall

what is cellulose?

long unbranched chains of beta glucose

how are cellulose microfibrils formed?

cellulose molecules hydrogen bond together to form a microfibril

where is cellulose mainly found in plants?

in the secondary cell wall

what is pectin composed of?

long complex polysaccharides rich in galacturonic acid

how can pectin resist compressive forces?

it binds cations, becomes hydrated, fills spaces and crosslinks with cellulose to form a gel like matrix

where is pectin mainly found?

in the primary cell wall and the middle lamella

what is the structure of a primary cell wall?

found between the plasma membrane and middle lamella

contains cellulose microfibrils, polysaccharides and pectin

what is the structure of wood?

made of dead plant cells with thick lignin rich secondary walls which form vertical channels

what is the role of lignin in wood?

to provide a high wet strength and rigidity

what are the main structural parts of the plant cell wall?

polysaccharides and some proteins

what are the proteins in the cell wall used for?

remodelling during growth and development

how can cellulose microfibrils resist stretching?

they have strong hydrogen bonds which resist expansion under high pressure

how can cellulose orientation affect plant growth?

it determines the direction of the cell elongation and can influence the tissue shape

how is the cellulose deposition directed?

the microtubules beneath the plasma membrane align with cellulose microfibrils and guide their orientation

how are microtubules involved in cellulose synthesis?

they act as tracks that guide the cellulose synthase enzyme complexes duringg deposition

what is the difference of ECM in connective and epithelial tissues?

connective = abundant ECM

epithelial = little ECM

what bears the mechanical stress in connective tissues?

the ECM

what transmits the mechanical stresses in epithelial tissues?

the cytoskeleton connected from cell to cell by adhesion junctions

what are some specialised connective tissues?

bone, cartilage and vitreous humour

what is the role of osteoblasts?

secrete the collagen matrix of the bone

what are the mineral parts of the bone ECM?

Calcium, magnesium , phosphate = hydroxyapatite

what is an osteon?

a structural unit of bone that is composed of concentric rings of mineralised matrix around a central cannal with blood vessels and nerves

is the bone cell sparse of cell dense?

cell sparse

where can cartilage be found?

in many joints and flexible structures

what are the properties of cartilage?

strong, flexible, shock absorbing, non mineralised

what is the cartilage ECM mainly made up of?

collagen and proteoglycans

what is the role of proteoglycans in cartilage?

they retain water and provide resistance to compressive forces

where is the vitreous humour located?

between the lens and retina in the eye

what is the vitreous humour made up of?

a clear, viscous gel of water, collagen and hyaluronic acid

what is unique about the vitreous humours cellularity?

virtually acellular

what is the most abundant protein family in the ECM?

collagen

how many collagen genes are in mammals?

over 40

in which tissues is collagen most abundant?

bone, tendons and skin

what is the structure of collagen assembly?

monomer → trimer →fibril→fibre

which cells secrete collagen?

fibroblast an other specialised connective tissue cells

how do fibroblasts organise collagen fibres?

they exert tension, pulling and alagning the collagen they secrete

how are collagen fibrils organsied in the skin?

in a plywood criscross pattern

how are collagen fibrils arranged in tendons?

in parallel along the axis of tension to resist stretching

what is the function of tendons?

they attach muscle to bone and transmit contractile force

in what form is collagen secreted?

as precursor molecules with peptide extensions

why are the peptide extensions present in the collagen precursor?

to preven premature fibril assembly inside the cell

what causes ehlers danlos syndrome and what happens?

the person has hyperextensible skin

results from mutations in collagen genes or in genes encoding proteins needed for collagen processing and assembly