11.2 Movement

The image below shows an electron micrograph cross section through a skeletal muscle.

 Identify structures A-C labelled in the image above.

The structures labelled E in the image in part a) are called myofibrils.
 

Describe the structure of a myofibril.

The structure labelled C in the image in part a) is 30 mm long when relaxed, but only 22.5 mm long when contracted.

Calculate the percentage decrease in length of the contracted structure C.

Suggest two reasons why it may be beneficial to study skeletal muscle fibres using an electron microscope rather than an optical microscope.

The image below is a transmission electron micrograph of a longitudinal section of skeletal muscle.

 Identify structures X, Y and Z.

Identify the molecules present in the regions labelled 1 and 2 in the image in part a).

During intense exercise the pH of skeletal muscle tissue falls sharply, causing alterations in the 3D structure of some calcium receptors within muscle fibres and lowering their contractile ability.

Use the information provided and your own knowledge to explain the reduced contractile ability of muscle fibres that results from intense exercise.

The table below describes three molecules involved with muscle contraction.

 Identify molecules A-C below.

Description	Molecule
Attaches to M line at the centre of the sarcomere	A
Hydrolysis of this molecule is required for the recovery stroke	B
Ion that diffuses across the sarcolemma	C

Outline how the filaments within muscle fibres slide past each other in the sliding filament mechanism of muscle contraction.

A recent discovery has shown that a third protein filament, known as titin, is also present in muscle fibres. The role played by titin is still being investigated, but one study looked at the effects of removing titin from the muscles of mice.

To remove the titin protein the mice had their muscles modified so that their titin filaments contained a cutting site for a plant enzyme called TEV protease. This meant that the scientists could use TEV protease to cut the titin proteins.

Suggest why the plant enzyme TEV protease was used rather than an animal protease.

The image below shows the location of titin within the sarcomere, as well as some of the results gained from the study described in part c) above.

Use the image and your existing knowledge to suggest a possible function of titin filaments.

Draw a labelled diagram of a sarcomere.

Describe the mechanism of muscle contraction from the point at which myosin binds to actin.

Explain how fluorescent dye can be used to show the role of ATP in muscle contraction.