cell moles2

Sliding filament model of contraction

1.ATP binds to a myosin head and forms ADP + P

2. Ca exposes the binding sites on the actin filaments 

3.Cross bridges between myosin head and actin filaments form

4.ATP causes the cross bridges to unbind

Skeletal muscle contration

- Tropomyosin-->7 actin-binding sites to 7 actin monomers In a thin filament 

- Troponin-->complex of 3 subunits(TN-T,TN-I,TN-C-binds Ca)

presence of Ca & TN-->TM can occupy ON And OFF state

OFF -> no Ca ->TM blocks myosin interaction with F-actin

ON -> binding to Ca -> movement of TM exposing myosin binding sites on actin

Smooth muscle contraction -> different from skeletal because of the presence of calmodulin and myosin light chain kinase (MLK) that lead to contraction

Actin and myosin in non-muscle cells

1.Support-->to epithelial cells-->adherens Junctions-->circumferential belt

2.Cytokinesis-->cell division-->accumulates at the Equator

3.Transport

4.Cell adhesion-->contractile bundles(myosin II) -> adherens junctions 

non-contractile bundles-->from the core of membrane Projections-->microvilli & filopodia

activity of myosin II was inhibited by deleting its gene or Injecting anti-myosin II antibodies into the cell-->a cell that lacked Myosin II was able to replicate its DNA and nucleus, but it didn't Divide-->a large & multinucleate cell

Membrane-bound myosin-->movement of vesicles

Myosin I & V-->move along actin filaments & carry Membrane vesicles 

Myosin V-->transports from Golgi to cell periphery