Actin is actually a globular protein that assembles as a long beady structure consisting of two helical chains.

Explanation

### Step-by-Step Solution:

1. **Understanding Actin**: Actin is a globular protein, known as G-actin (globular actin), which plays a crucial role in muscle contraction and cellular movement.

2. **Structure of Actin**: G-actin monomers polymerize to form F-actin (filamentous actin), which consists of two helical chains. These chains coil around each other, creating a long, beady structure.

3. **Role in Muscles**: Actin is a contractile protein found in muscle cells. It is a key component of the sarcomere, the basic unit of muscle contraction.

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