Muscles And Synapses L7 Flashcards
Multiple myofilaments
- several myosin and actin filaments are interacting = sliding filament theory of muscle contraction
- even tho the sacromere shortens, the length of each myofilament does not change. However the width of the H zone changes
The 5 different molecules involved in slipping filament theory
1) myosin
2) actin
3) trpomyosin
4) troponin
5) ATP
6) calcium ions
In skeletal muscle cells, myosin are bundles together to form the
Thick filament
The cross bridge (head) of the myosin module has the ability to
Move back and forth, this movement provides power stroke for muscle contraction
The cross bridge has two binding sites, one site binds to
ATP (low E conformation), hydrolysis = (high E conformation) and the other binds to actin.
______ is a major component in the thin filament
Actin, each actin subunit has binding site to which myosin crowd bridge binds to
The actin portion of the thin filament is composed of actin subunits twisted into a
Double helical chain
Tropomyosin is part of the thin filament ?
YES
Tropomyosin wraps around actin, in unstimulated muscle, the tropomyosin wraps around
binding sites of actin, preventing myosin cross bridge form binding
In order to move tropomyosin and myosin aside to expose the binding sites,
Troponin attaches and and is spaced periodically along tropomyosin strand
After an AP, calcium ions are released from the terminal cisternae and bind to troponin. This causes conformational change in the
tropomylosin-troponin complex, dragging the tropomyosin strands off the bidning site
6 steps of cross bridge cycling
1) the influx of calcium, triggers the exposure of binding steps on actin
2) binding of myosin to actin
3) the power stroke of the cross bridge that causes the sliding of the thin filaments
4) the binding of ATP to the cross bridge, which results in the cross bridge disconnecting from actin.
5) hydrolysis of ATP = re-energizing the repositioning of the cross bridge
6) the transport of calcium ions back into the sacroplamic reticulum
STEP 1: exposure of binding sites on actin
- AP binds calcium ion form terminal cisternae of thesacroplasmic recticulum
- Ca flood into cytosol and bind to the troponin, causing a change in conformation of the troponin-tropomyosin complex = exposing the binding sites
STEP 2: binding of myosin of actin
When a binding site on actin is exposed, an energized cross bridge binds to it
STEP 3: power stroke of the cross bridge
- the binding of myosin to actin about a change in the conformation of the cross bridge, resulting in the release of ADP inorganic phosphate
- cross birdge flexes, pulling the thin filament inward toward Center pol the sacromere = power stroke
- the chemical E of ATP is transformed onto mechanical E of a contraction
STEP 4: disconnecting the cross bridge actin
In order to disconnect the cross bridge form actin, ATP must bind on the myosin cross bridge
STEP 5: re-energizing and repositioning the cross bridge
- the release of the myosin cross bridge form actin triggers the hydrolysis of the ATP
- E transferred form ATP top my sos in bridge, which returns to its high E conformation
STEP 6: removal of calcium ions
- calcium is actively transported form the cytosol into the sacroplamsic recticulum by ion pumps
- Ca removed, troponin-tropomyosin complex again covers the binding site.
During contraction, all cross bridges are
Neither bound nor disconnected at the same time
Ca pumps
Active transport moves Ca in sacroplasmic recticulum
- ATP hydrolysis
Role of ATP
1) energizing power stroke of the myosin cross bridge
2) disconnecting myosin courses bridge from BS on actin act the conclusion of the power stoke
3) pumping Ca back into the sacroplasmic recticulum
Types of muscle fibre
- white muscle fibre
- red muscle fibre
Features of white muscle fibre
- large
- light colour cuz of reduced myoglobin
- surrounded by few capillaries
- few mitochondria
- high glycan (glycolysis)
(Small O2 amount available, powered by glyoclysis cuz doesn’t use O2)
Features of red muscle fibres
- small
- dark colour = lots of myoglobin
- many capillaries
- lots of mitochondria
- low glycan
(Use KREBS and oxidative phosphorylation, which require mithcodornia and O2)
Metabolism in white muscle fibres
- muscle w many WMF are better for activities requiring speed and power for short duration.
- glycolysis = synthesizes ATP quickly
- cross bridge cycling occurs in fast contractions (fast twitch glycolytic fibres )
- fatigue rapidly due to lactic acid build up
And depletion of glycogen
Metabolism of red muscle fibres
- muscle w many RMF are better for activates needing endurance
- Krebs and oxidative phosphorylation = ATP
- cross bridge cycling occurs slowly (slow-twitch oxidative fibres)
- fatigue resistant, high endurance
