In this IBDP Biology post, we will be understanding the different types of relaxation as well as contraction of the muscles.
Myosin Filaments: Relaxed and Contracted Muscles
1. Myosin heads form cross-bridges and then attach to binding sites on Actin
2. ATP binds to Myosin heads which cause them to break cross-bridges and detach from binding sites
3. ATP is hydrolised to ADP and Phosphate provides energy for Myosin heads to change angle and swievel outwards away from sacromere centre
4. Heads attach to the binding side of Actin that are further from the centre of the sacromere than the previous site (new cross-bridges)
5. ADP is released and the heads push the Actin filament inwards towards the centre of sacromere
Actin Filaments: Relaxed and Contracted Muscles
1. Motor neuron stimulates muscle
2. Calcium ions are released from the Sacroplasmic Reticulium into muscle fibre
3. Calcium binds to troponin and causes Actin to change shape
4. The changed shape of Actin causes tropomyosin to move exposing the binding sites on Actin
5. When the Myosin heads binds to Actin, the filament swievels to the centre of the sacromere forming cross-bridges
Aequorin and Calcium Contraction
- Ashley and Ridgway studied the role of Calcium in the relationship between nerve impulses and muscle contraction
Aequorin: Calcium binding bioluminescent protein
When Calccium binds to Aequorin it emits light. The timing of the light emission between the arrival of an electrical impulse and the contraction of a muscle fibre.
This action is consistent with the release of Calcium from the Sacroplasmic Reticulum
The light emissions are detected and recorded using specialised microscopes and cameras
Researchers have also used fluorescent dyes to visualise and measure the movement of Actin and Myosin
Aequorin and Fluorescent dyes only emit light for a few nano seconds therefore they are ideal to measure the rapid movements of muscle cells
That's all!
Drafted by Venetia (Biology)