Contraction and Chemotaxis
Stress fibres are actin bundles that can contract and produce force.
Integrins are a component of focal adhesion, part that contacts extracellular
Actin filaments are organized in contractile bundles (ability to get shorter and when
contract, generate force that pulls cell forward)
How do you pull?
The blue structures that are not labelled and made up of myosin protein which is
capable of producing force (pushing and pulling).
Myosin is major component of muscle.
Myosin has a nucleotide binding site (ATP) and actin binding site. It converts
chemical energy from ATP and translate it into mechanical work.
Myosin is a protein that produces force.
“Motor Proteins” that convert chemical energy in the form of ATP into mechanical
Motor proteins are able to convert 65% of the chemical energy found in ATP
into mechanical work.
Myosin motor domain, head domain has binding pocket for ATP, binds to actin
filament and undergoes large conformational change which the release of phosphate
after hydrolyzes ATP and conformational change exerts pull. Class:
I – Membrane association and endocytosis
II – Contraction
V – Organelle transport
Non-Muscle Myosin-II forms bundles that pull actin filaments inward.
Myosin wants to go toward plus end of the actin, so both sides contract and this is
how they pick up their back feet.
Different actin networks exist at the front and back of the cell.
Front end - dendritic arp2/3 arrays of actin -- treadmilling machine
At the back - need contractile bundles that connect to focal adhesions that
eventually pull cell forward – stress fibres
How does it know to put the lamellipodium at front and stress fibres in the back?
Dictyostelium is an amoeba that aggregates with other amoeba upon starvation
Unicellular organisms that is able to stop being unicellular and become
multicellular - usually happens under starvation.
create a slug and start behaving like a multicellular animal - create a fruiting body
with a ball of spores