5.5.11: Muscle contraction Flashcards
What is creatine phosphate?
A compound in a muscle that acts as a store of phosphates and can supply phosphates to make ATP rapidly.
What are myofibrils and what do they contain?
- They are the contractile units of skeletal muscle and contain two types of protein filament:
- Thin filaments, which are aligned to make up the light band. These are held together by the z line.
- Thick filaments, which make up the dark band.
How much overlap is there between the thick and thin filaments?
- The thick and thin filaments overlap, but in the middle of the dark band there is no overlap.
- This is called the H zone.
What is the distance between two Z lines called?
-A sarcomere.
What is the function and size of the sarcomere?
- This is the functional unit of the muscle.
- At rest, a sarcomere is about 2.5 um long.
What are the thick and thin filaments surrounded by?
Sarcoplasmic reticulum.
What are the thin filaments made up of?
- Actin
- Each filament consists of two chains of actin subunits twisted around each other.
- Wound around the actin is a molecule of tropomyocin to which are attached globular molecules of troponin.
What does each troponin complex consist of?
- Three polypeptides.
- One binds to actin, one to tropomyosin and the third binds to calcium when it is available.
What is the function of tropomyosin and troponin?
- Tropomyosin and troponin are part of the mechanism to control muscular contraction.
- At rest, these molecules cover binding sites to which the thick filaments can bind.
What does each thick filament consist of?
- A bundle of myosin molecules.
- Each myosin molecule has two protruding heads, which stick out at each end of the molecule.
- These heads are mobile and can bind to the actin when the binding sites are exposed.
Which observation led to the sliding filament hypothesis?
- During contraction, the light band and the H zone get shorter.
- Therefore, the Z lines move closer together and the sarcomere gets shorter.
- During contraction, the thick and thin filaments slide past one another.
What is the sliding action in muscles caused by?
- The movement of the myosin heads.
- When the muscle is stimulated, the tropomyosin is moved aside, exposing the binding sites on the actin.
- The myosin heads attach to the actin and move, causing the actin to slide past the myosin.
Describe the stages in the control of muscle contraction.
Step 1:
- When the muscle is stimulated, the action potential passes along the sarcolemma and down the transverse tubules into the muscle fibre.
Describe the stages in the control of muscle contraction.
Step 1: When the muscle is stimulated, the action potential passes along the sarcolemma and down the transverse tubules into the muscle fibre.
Step 2:
- The action potential is carried to the sarcoplasmic reticulum, which stores calcium ions, and causes the release of calcium ions into the sarcoplasm.
Describe the stages in the control of muscle contraction.
Step 2: The action potential is carried to the sarcoplasmic reticulum, which stores calcium ions, and causes the release of calcium ions into the sarcoplasm.
Step 3:
- The calcium ions bind to the troponin, which alters the shape pulling the tropomyosin aside. This exposes the binding sites on the actin.