The cross bridge cycle
Discipline: Biology (and other Life Sciences)
Type of Paper: Question-Answer
Academic Level: Undergrad. (yrs 3-4)
Paper Format: APA
Question
The cross bridge cycle starts when _________. select one
1.ATP binds to troponin and is hydrolyzed to ADP and Pi
2.acetylcholine diffuses away from the synaptic cleft
3.Ca2+ is actively transported into the sarcoplasmic reticulum
4.Ca2+ from the sarcoplasmic reticulum binds to tropomyosin
5.Ca2+ from the sarcoplasmic reticulum binds to troponin
Expert Solution Answer
5.Ca2+ from the sarcoplasmic reticulum binds to troponin
Influx of sodium ions depolarizes the membrane (activation) and the membrane becomes positively charged inside. This membrane activation triggers the release of Ca2+ from the sarcoplasmic reticulum. These calcium ions bind to the troponin in the muscle filament, which causes the exposure of myosin binding sites.
Actin-myosin cross bridges are formed, actin filaments contract over the stationary myosin filaments. After the action potential ends, the Ca2+ detaches and removed by active transport into sarcoplasmic reticulum, and the muscle fiber relaxes.