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Esdin LS 2 Lec 5 Muscles

For myosin thin filament tropomyosin troponin

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Unformatted text preview: bular protein that polymerizes to form an intertwined helix •  Actin has a binding site for myosin Thin Filament + Tropomyosin Troponin •  Tropomyosin is arranged like a ribbon that binds the myosin binding site on the actin physically covers the actin/myosin combination site 7 4/21/13 Thin Filament + Tropomyosin Troponin connects tropomyosin to actin •  Troponin is made of three spherical subunits. It contains three binding site –  Actin binding site –  Tropomyosin binding site –  Calcium binding site What Happens During Muscle Contraction? Muscle relaxed Muscle contracted forced production 8 4/21/13 What Causes Binding to Occur? •  Two major components 1. ATP: comes from the mitochondria 2. Calcium ATP Source Citric acid cycle Pyruvate oxidation Glycolysis Cytosol Mitochondrial matrix Mitochondrial inner-membrane Electron transport chain cristae 9 4/21/13 Where Does Calcium Come From? •  Calcium is a very important ion that has numerous functions •  Its high intracellular level can be toxic and therefore must be maintained at a very low level at all times inside the cell (10-9 M) no activity in the muscle at this level, activity when it hits 10^-7 calcium comes from the inside of the cells instead of the outside calcium is not found in the cytoplasm, stored in the smooth ER Sarcoplasmic Reticulum Is a Modified Smooth ER •  Stores calcium 10 4/21/13 Sarcoplasmic Reticulum Is a Modified Smooth ER •  Sarcoplasmic reticulum found around the myofibrils •  The lateral sacs are the end segments that release calcium upon stimulation •  Calcium release is triggered by series of events Muscle Cell •  Muscle cells have a modified plasma membrane known as sarcolemma •  The sarcolemma has extensions (invaginations) that dip deep into the cytoplasm •  These invaginations are known as Ttubules 11 4/21/13 Muscle Cell Sarcoplasmic reticulum store calcium Myofibrils Transverse tubule T- tubule Lateral sacs releases calcium T-Tubules & SR •  Special voltage sensitive calcium channels known as dihydropyridine receptors (DHPR) are located on the Ttubules •  Ryanodine receptors (foot proteins) are located on the lateral sacs of the SR 12 4/21/13 T-Tubul...
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