MYTUTOR SUBJECT ANSWERS

356 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

6 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

150 SUBJECT SPECIALISTS

£20 /hr

Anna H.

Degree: Anthropology (Bachelors) - Durham University

Subjects offered: Biology, Drama

Biology
Drama

“About me: Hi I’m Anna and I’m in first year, studying Anthropology at Durham University. My course has a fair bit of biology in it (genetics, evolution, health, disease etc.), and I also did Biology at A level, along with Geography an...”

MyTutor guarantee

£20 /hr

Catherine T.

Degree: BSc Medical Sciences with Professional Training Year (Bachelors) - Exeter University

Subjects offered: Biology, Science+ 3 more

Biology
Science
Human Biology
Extended Project Qualification
English Literature

“Aims and methods: I focus on breaking things down in to easy to digest pieces of information and will use a variety of methods to look at an aspect of your course. I will aim to make things clear and easy to remember, whilst also hopi...”

MyTutor guarantee

£20 /hr

Emma D.

Degree: Philosophy and Psychology (Bachelors) - Durham University

Subjects offered: Biology, Philosophy and Ethics+ 2 more

Biology
Philosophy and Ethics
Maths
-Personal Statements-

“First year Durham University student with exepertise in Maths, Biology and Religious Studies.  Friendly, dedicated and personable student who has prior experience working as a tutor and advisor. ”

MyTutor guarantee

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

Why does the thickness of the heart's chamber walls vary?

When do mutations not cause a change in amino acid sequence?

Genetics: How does our genotype influence our phenotype?

How does the Meselson and Stahl Experiment provide evidence for the semi conservative theory of DNA replication?

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