The structure myosin II essay - stuck on word count

Okay so the essay title is 'Explain how the structure of myosin II relates to its function in muscle action' and it needs a maximum of 1500 words. Basically I have written a few things but I've got to 500 words and am a little stuck. What on earth can i write about that will pack out the word count? Any advice would be much appreciated. Thanks :) in advance

It will be much easier to help you, once you post what you've got so far. Don't panic, just send what you have, and we'll have a look at how we can help you fluff it up!

:)

okay ive done this much

Muscle contraction is fundamental process that allows locomotion to occur. The structures of the proteins involved are key to enabling muscle action to work. Myosin is one of the major proteins that works in conjunction with actin and others to make muscles contract in muscle cells. 55% of the weight of a muscle is myosin.

Myosin II has a very specific structure that allows it to carry out its function effectively. A molecule of myosin is made up of 6 main component chains; 2 'heavy chains' which are both around 2000 amino acids in length and 4 'light chains'. The 'heavy chains' have an N-terminus head and a C-terminus end which takes the shape of an alpha helix. The alpha helix sections of the 2 heavy chains, coil around each other tightly to form a dimer (Cooper, 2000).Therefore each molecule of myosin has 2 heads on it. There are 2 light chains associated with each head on the heavy chain and they bind around the 'neck' region (between the head and tail). There is one regulatory light chain and an essential light chain that have different roles in the myosin molecule. Hundreds of myosin molecules group together to form thick filaments which are part of the sliding filament model which illustrates how muscle contraction works.

Muscle contraction begins when a calcium ion (Ca2+) binds to troponin, another protein that makes up muscle fibres. This results in a second protein, tropomyosin being moved out of the way, uncovering the binding sites where myosin can bind to the actin myofilaments. On the myosin head, there is a molecule of ADP and an inorganic phosphate from the previous muscle contraction cycle. The heads are now able to bind to the newly revealed binding sites on the actin filament. This forms cross bridges and the phosphate is released. The release of the phosphate induces a conformational change in the shape of the myosin head (Wikipedia, 2012). This conformational change causes the 'power stroke' which drives the movement of the actin filaments past the myosin filaments (Murray et al, 2009). The ADP molecule is released from the myosin head as movement occurs. The next molecule of ATP arrives and binds to the myosin head which stops the interaction between myosin and actin. The ATP is hydrolysed to ADP and an inorganic phosphate, the myosin heads return to their initial positions and so the muscle contraction cycle continues as long as there are more calcium ions present. The constant attaching and detaching of actin and myosin from one another allows muscle action to occur.

The structure of myosin II allows it to perform the power stroke and allow muscle contraction occur. The head on the myosin molecules must be the correct shape that is complementary to the binding site on the actin filament. If the shape was wrong then myosin would be unable to bind to actin then the power stroke and muscle contraction would not occur.

Muscle contraction is a fundamental process that allows locomotion to occur. The structures of the proteins involved are key to enabling muscle action to work. Myosin is one of the major proteins that works in conjunction with actin and others to make muscles contract in muscle cells. 55% of the weight of a muscle is composed of myosin.

This is a good factual essay. I can't determine the accuracy of the facts, sorry :)
Good luck, and can you look at mine?