BIOL2200 Lecture Notes - Lecture 5: Macrophage, Phosphatidylinositol, Filopodia

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30 Jun 2018
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CYTOSKELETON LEC 2 BIOL2200
Lecture 2: actin-based structures and motility
Overall structure of a muscle fibre each fibre is a result of multinuclecic cells - Dark areas.. Light
areas… biochemically characterised sarcomere
The sarcomere: unitary structure of skeletal muscle
oEach sarcomere contains two types of filaments: thick filaments of myosin II and thin
filaments of actin
oZ Disc - anchors thin filaments
oI band - thin filaments only
oA band - overlapping thin and thick filaments
oH zone - thick filaments only
The sliding filament model of skeletal muscle contraction only change is in the overlap of
the filaments during muscular contraction
oThe decreased in sarcomere length is due to decreases in the width of the I band
and H zone, with no change in the width of the A band. The lengths of both the thick and
thing filaments do not change during contraction
oThe thick and thin filaments slide along one another, increasing their overlap and so
pulling the Z discs closer together organisation is slightly different for cardiac muscle
Microfilament motors: regulation by calcium rigor mortis due to lack of atp
oRelease of Ca2+ from the Sarcoplasmic reticulum (SR) triggers contraction
oReuptake of Ca2+ into SR relaxes muscle
oTropomyosin ™ and troponin (TN) are accessory molecules bound to actin thin
filaments
oIn the absence of calcium, TM and TN molecules block the interaction of myosin the
F actin
oIn the presence of calcium, TN induced TM to move to a new site, exposing the
myosin-binding sites on actin
Myosin type II coincides with actin staining in cells
oLabile bipolar myosin II filaments are founds in the stress fibres of non-muscle cells
Microfilament motors
oCytokinesis required myosin II
oType I myosins (unconventional) tail usually associates with some sort of
intracellular organelle
Single-head motors (monomers)
Uses ATP hydrolysis
Localised to the cell periphery
Involved in organelle and vesicle transport
oCell motility requires myosin I nomenclature of the cells when movement: head,
tail, leading edge, thin area of membrane is called LAMELIPODIUM
oMyosins are required to transport membranous organelles to the cell membrane
Cell motility requires myosin I periphery of the cell
Actin configuration in cells, stress fibres and cortical actin variety of configurations
Cell migration
oCells migration results from the coordinated formation of actin filament bundles and
networks in cells
oCells need to attach to their substratum in order to move (focal adhesions) if too
strong, cant move.. Too weak, no friction, cant move
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