Question

1. Calmodulin is found in smooth muscle cells and performs a similar function to troponin in striated muscle fibers. However, calmodulin not only gets activated by Ca2+ but also slows the release of Ca2+ from the sarcoplasmic reticulum. How might this difference relate to the different kinds of contractions smooth muscles do in comparison to striated muscles?

2. A study of muscle fibers between chimpanzees and humans revealed that although muscle mass per body size is approximately equivalent, the ratio of red (slow) and white (fast) fibers were significantly different. Chimps tend to have a ratio of 30% red to 70% white where humans are 60/40 respectively. Speculate about what this ratio difference means in terms of muscle activity potential and a possible evolutionary significance of this difference.

3. Fleas can jump up to 40 times their body length. However, calculation on the biomechanics of the leg extensor muscles, do not provide enough force to account for such jumps. If the flea's ability to jump high is not reliant upon muscle strength, how else could the leg structure be modified to assist in the flea jumping mechanism? How would you test your idea?

Answer 1

Answer:

$\rightarrow$ Smooth and Skeletal muscle contraction process:

Smooth Muscle	Skeletal Muscle
Muscle excitation	Muscle excitation
↓	↓
Rise in Cytosolic Ca2+ (majorly from extracellular fluid)	Rise in Cytosolic Ca2+ (fully from intracellular sarcoplasmic reticulum)
↓	↓
Ca2+ binding to calmodulin	Physical repositioning of troponin and tropomyosin
↓	↓
Phosphorylation of myosin in thick filament	Uncovering of cross-bridge binding sites on actin in thin filament
↓	↓
Binding of Actin and Myosin	Binding of Actin and Myosin
↓	↓
Muscle contraction	Muscle contraction

As shown above, the main differences between Smooth and Skeletal muscle contraction are:

• Extracellular fluid is the major source for Ca2+ in smooth muscle contraction, whereas intracellular sarcoplasmic reticulum is the source for Ca2+ in Skeletal muscle contraction
• Calmodulin involves in smooth muscle contraction, whereas troponin and tropomyosin are involved in skeletal muscle contraction
• Myosin in thick filament involves in smooth muscle contraction, whereas actin in thin filament involves in skeletal muscle contraction

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