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Lecture 22.doc

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McGill University
Biology (Sci)
BIOL 201
Gary Brouhard

Lecture 22 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 matrix. 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 work 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
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