Cell Adhesion Flashcards
How to cells transmit physical stresses?
i) extracellular matrix
ii) cytoskeleton and cell-cell adhesions that connect the cytoskeletons of neighbouring cells
plants use ECM
animals use both in different tissue types
What is the most common additional polymer in the secondary cell wall?
lignin
What gives the wall its tensile strength?
cellulose microfibrils, composed of ~16 cellulose molecules with each molecule being made of 100s of glucose subunits
found in plants
What are some roles of pectin?
provides resistance to compressive forces
highly hydrated, binds cations
space filling effect
crosslinks w cellulose to form a matrix
found in plants
Where are cellulose microfibrils predominantly found?
secondary cell wall
Where is pectin abundant?
primary cell walls
What is the function of the middle lamella?
cements primary cell walls of adjacent plant cells together
What molecule is the middle lamella abundant with?
pectin
What are some properties of lignin?
complex polymer of crosslinked phenolic compounds
high wet strength (rigid when wet)
How is cellulose synthesised?
by the cellulose synthase complex which is physically linked to underlying microtubules which guide the enzyme complex
What are the bone forming cells that secrete collagen matrix?
osteoblasts
What are osteons?
a collection of concentric rings composed of mineralised matrix deposited around a central canal containing blood vessels and nerves
What is hydroxyapatite composed of?
calcium, magnesium and phosphate ions
What is collagen and where is it found?
protein molecules made up of amino acids
provides structural support to the extracellular space of connective tissues
found in skin, tendons, bones, and ligaments
What are some properties of cartilage?
found in many joints
strong, flexible
large amounts of ecm (collagen)
no mineralisation
~25% total protein mass in a mammal
>40 collagen genes in mammals
Where is the vitreous humour found and what is it?
between lens and retina in the eye
clear, viscous gel
composed of water, collagen, hyaluronic acid
virtually acellular
What is an example of a collagen-producing cell?
fibroblast
What is the sequence of collagen organisation?
monomer -> trimer -> fibril -> fibre
How is collagen arranged in skin?
plywood like pattern allowing resistance to tensile stress in multiple directions
How is collagen arranged in tendons?
tendons attach muscle to bone
collagen fibres align in parallel, along axis of extension
How do fibroblasts influence the alignment of collagen fibres?
they pull on and shape the collagen they have secreted
fibroblasts at the end of a wound become migratory to close the wound
In what form is collagen secreted
procollagen, which has additional peptide extensions that obstruct premature fibril assembly
How does procollagen form collagen?
procallagen proteinases cleve terminal extensions
the new mature collagen molecules self assemble into collagen fibrils outside of the cell
What is the primary function of fibronectin and integrins?
help cells attach to the ECM
fibronectin acts as a molecular bridge between integrins and the ecm
What do integrins exist as?
heterodimers with alpha and beta subunits
What is the structure of fibronectin?
exists as a homodimer bonded by disulphide bonds at one end
has a cell attachment site eg via integrin
has an ecm binding site eg via collagen