MYTUTOR SUBJECT ANSWERS

266 views

Why is ATP required for skeletal muscle contraction?

When muscles contract, the length of the sarcomere (distance between the Z-lines*) shortens. ATP is required for the process of cross-bridge cycling which enables the sarcomere to shorten. The steps of cross-bridge cycling are as follows:

When ADP** is bound to myosin heads, they are able to bind to actin filaments of the adjacent myofibril to form a cross-bridge. Once they are attached, the myosin filaments change their angle, pulling back the actin filaments in a power stroke, releasing the ADP molecule in the process. This causes the sarcomere to shorten. Now, an ATP molecule binds to the myosin head, causing it to detach from the actin filament. The enzyme ATPase catalyses the breakdown of ATP to ADP and inorganic phosphate, which releases energy for the myosin head to return to its original position in a recovery stroke. Recall that myosin can only bind to actin when it has ADP attached, so myosin is now poised to bind once again to another actin molecule to contract the muscle further, and our cycle continues. Crucially, we need ATP to enable the actin-myosin cross-bridge to detach, and release energy through its hydrolysis to enable the myosin head to return to its resting position. Without this vital role of ATP, the cross-bridges will stay permanently bound, and the muscle will not be able to contract further, relax or initiate a new contraction. This is why, after death, when ATP is no longer being produced through respiration, muscles are permanently contracted, a condition known as rigor mortis.

ATP is also required to enable skeletal muscle to prevent further contractions when a muscle is no longer stimulated. If you recall, when a skeletal muscle is stimulated to contract, we need calcium to bind to the globular protein troponin, which causes the threadlike protein tropomyosin (which wraps itself around the actin filament) to pull away, leaving actin free to bind to myosin. To stop a muscle continually contracting after its stimulation has ended, calcium is taken up again by the sarcoplasmic reticulum*** by active transport through calcium ATPase. This requires energy from the hydrolysis of ATP.  

*Z-line marks the end of the sarcomere and is the attachment point for actin filaments at each end of the sarcomere.
**ADP is one of the products of ATP hydrolysis by the following reaction:  ATP à ADP + Pi (+ energy released).
***the specialised endoplasmic reticulum of muscle.

Surina F. A Level Biology tutor, GCSE Biology tutor

5 months ago

Answered by Surina, an A Level Biology tutor with MyTutor


Still stuck? Get one-to-one help from a personally interviewed subject specialist

118 SUBJECT SPECIALISTS

£20 /hr

Roshni R.

Degree: Dentistry (Bachelors) - Birmingham University

Subjects offered: Biology, Spanish+ 4 more

Biology
Spanish
Maths
Chemistry
-Personal Statements-
-Medical School Preparation-

“Tutoring approach Professional but friendly approach.  Work with my students to identify the areas the student is finding most difficult. Review the topic with my hand-written notes.  Explain any misunderstood areas. Work through examp...”

£20 /hr

Georgina H.

Degree: Marine Sciences (Doctorate) - Newcastle University

Subjects offered: Biology, -Personal Statements-

Biology
-Personal Statements-

“About me I am currently in my first year of my PhD at Newcastle University. From a young age, I have always been captivated by science and the natural world, which in turn has inspired me to pursue a doctorate degree in Marine Scien...”

MyTutor guarantee

£20 /hr

Victoria S.

Degree: Physiology (Bachelors) - Liverpool University

Subjects offered: Biology, Maths

Biology
Maths

“About me:Hey! My name is Tory and I am in my second year studying Physiology in the School of Life Sciences at The University of Liverpool. After completing my current degree, I hope undertake a Graduate-entry Medicine course to furt...”

About the author

Surina F.

Currently unavailable: for new students

Degree: Medicine (Bachelors) - Cambridge University

Subjects offered: Biology, Chemistry+ 2 more

Biology
Chemistry
-Oxbridge Preparation-
-Medical School Preparation-

“About me I am a medical student at Cambridge University. As long as I can remember, I have been fascinated by the study of our bodies and the other living organisms surrounding us. I think that studying Biology offers a fantastic oppo...”

You may also like...

Other A Level Biology questions

What is the function of the myelin sheath?

What causes bacteria to become antibiotic resistant?

How are blood glucose levels controlled in the body?

How is meiosis different to mitosis?

View A Level Biology tutors

Cookies:

We use cookies to improve our service. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok