Concept explainers
Active sites on actin become available for binding when
(a) calcium binds to troponin.
(b) troponin binds to tropomyosin.
(c) calcium binds to tropomyosin.
(d) actin binds to troponin.
Introduction:
Muscles are made up of two main protein filaments namely, a thick filament that is made up of a protein called myosin and a thin filament that is composed of a protein known as actin. When these two filaments crossover one another in a row of repetitive events then muscle contraction takes place.
Answer to Problem 1RFT
Correct answer:
Thin filament consists of regulatory proteins called tropomyosin and troponin and the calcium ions binds with the troponin.
Explanation of Solution
Explanation for the correct answer:
Option (a) is given as calcium binds to troponin. The muscle contraction takes place in a series of steps. The cycle starts with electrical events in the sarcolemma. This accelerates the generation of calcium ions from the cisternae of the sarcoplasmic reticulum. The calcium ions then enter the zone of overlap. The next step involves binding of these calcium ions to troponin in the complex of troponin-tropomyosin. This alters the position and rolls the tropomyosin molecule away from the active sites present on the actin. This makes the active sites exposed for the formation of cross-bridges. Hence option (a) is correct.
Explanation for the incorrect answers:
Option (b) is given as troponin binds to tropomyosin. Troponin binds to the troponin-tropomyosin complex and rolls away from the tropomyosin complex. So, it is a wrong answer.
Option (c) is given as calcium binds to tropomyosin. Calcium binds to the troponin molecule instead of tropomyosin molecule. So, it is a wrong answer.
Option (d) is given as actin binds to troponin. Troponin binds to the calcium and makes actin sites exposed. So, it is a wrong answer.
Hence, option (b), (c) and (d) are incorrect.
Therefore, it can be concluded that calcium ions bind to the troponin and this troponin then binds to the troponin-tropomyosin complex, making active sites exposed during muscle contractions.
Want to see more full solutions like this?
Chapter 9 Solutions
HUMAN ANATOMY PACKAGE
- Do all three types of muscle: smooth, skeletal, and cardiac use cross bridges for movement of muscles? What about tropinoin and tropomysin? Is it only skeletal and cardiac that utilize these specific myosin and actin components?arrow_forwardList the various Myofibril Structures?arrow_forwardWhat event causes a troponin-tropomyosin complex to regain its original shape in muscle relaxation? a. stimulation of ACh receptors b. diffusion of Na+ back into transverse tubules c. return of Ca2+ into the sarcoplasmic reticulum d. breaking of the bond with tropomyosinarrow_forward
- Explain why myosin II in a sarcomere can produced force only for that sarcomere contraction and not for that sarcomere extension?arrow_forwardWhat two types of microfilament make up the muscle sarcomere? Which motor protein is primarily involved in muscle contraction?arrow_forwardMuscle relaxation occurs when ________. a. calcium ions are actively transported out of the sarcoplasmic reticulum b. calcium ions diffuse out of the sarcoplasmic reticulum c. calcium ions are actively transported into the sarcoplasmic reticulum d. calcium ions diffuse into the sarcoplasmic reticulumarrow_forward
- How are myofilaments and sarcomeres of myofibrils related?arrow_forwardFigure 13.22 To what structures in a skeletal muscle are the endoneurium, perineurium, and epineurium comparable? Figure 13.22 Close-Up of Nerve Trunk Zoom in on this slide of a nerve trunk to examine the endoneurium, perineurium, and epineurium in greater detail (tissue source: simian). LM × 1600. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)arrow_forwardHow does a muscle fiber incur an oxygen debt?arrow_forward
- what is a myofibrilarrow_forwardWhich region or organelle—cytosol, mitochondrion, or SR—contains the highest concentration of calcium ions in a resting muscle fiber? Which structure provides the ATP needed for muscle activity?arrow_forwardHow would muscle contractions be affected if skeletalmuscle fibers did not have T-tubules?arrow_forward
- Human Physiology: From Cells to Systems (MindTap ...BiologyISBN:9781285866932Author:Lauralee SherwoodPublisher:Cengage LearningAnatomy & PhysiologyBiologyISBN:9781938168130Author:Kelly A. Young, James A. Wise, Peter DeSaix, Dean H. Kruse, Brandon Poe, Eddie Johnson, Jody E. Johnson, Oksana Korol, J. Gordon Betts, Mark WomblePublisher:OpenStax CollegeHuman Biology (MindTap Course List)BiologyISBN:9781305112100Author:Cecie Starr, Beverly McMillanPublisher:Cengage Learning