All proteins -

Options

A. Are enzymes
B. Are homopolymer
C. Consists of one or more polypeptide chains
D. Have a linear or flat shape

Answer

### Step-by-Step Solution:

1. **Understanding Proteins**: Proteins are essential biomolecules that play a variety of roles in biological systems. They are made up of smaller units called amino acids.

2. **Composition of Proteins**: Proteins are polymers of amino acids. However, they are not homopolymers because they are made from 20 different types of amino acids, which makes them heteropolymers.

3. **Structure of Proteins**:
- The primary structure of a protein refers to the linear sequence of amino acids linked by peptide bonds.
- As the protein folds, it can form secondary structures such as alpha helices and beta-pleated sheets.
- The tertiary structure refers to the overall three-dimensional shape of the protein, which can be globular or fibrous.

4. **Distinction Between Proteins and Enzymes**: Not all proteins are enzymes, but all enzymes are proteins. This means that while enzymes are a specific type of protein that catalyzes biochemical reactions, there are many proteins that do not have enzymatic functions.

5. **Final Note on Protein Structure**: The shape of proteins is crucial for their function. The folding and interactions between different parts of the protein determine its specific role in the cell.