Q.(a) Name the protein found in the light and dark bands of myofibril respectively. [2M]

If you have ever noticed that some cuts of meat look deep red while others look pale, you have already met the idea behind muscle fibre types. Not all skeletal muscle fibres are built the same way; they differ in colour and, more importantly, in how they get the energy to keep working. The difference comes down largely to a red, oxygen-storing pigment called myoglobin and to how each fibre chooses to make its ATP.

Myoglobin is the key character. It is a reddish pigment that holds a store of oxygen inside the muscle. A fibre packed with myoglobin looks red and has oxygen on hand; a fibre with very little myoglobin looks pale. This single difference sorts fibres into two broad kinds.

• Red fibres have a high content of myoglobin, which gives them their reddish colour. They also carry plenty of mitochondria, the structures that use the stored oxygen to produce ATP. Because they rely on oxygen to make their energy, red fibres are also called aerobic muscles. Their large oxygen store lets them keep working steadily.
• White fibres have very little myoglobin, so they look pale or whitish. They have few mitochondria, but the amount of sarcoplasmic reticulum inside them is high. For their energy they depend not on oxygen but on an anaerobic process — making ATP without using oxygen. …