At some points a protein molecule may be folded back on itself. This called _____ structure and folds or coils are held together in place by _______.

Options

A. a) `2^(@)`, H-bonds
B. b) `2^(@)`, peptide bonds
C. c) `3^(@)`, H-bonds
D. d) `1^(@)`, peptide bonds

Answer

To solve the question, we need to identify the type of protein structure that involves folding back on itself and the type of bonds that hold these folds or coils together.

### Step-by-Step Solution:

1. **Understanding Protein Structures**:
- Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.
- The primary structure is the linear sequence of amino acids connected by peptide bonds.

2. **Identifying the Structure**:
- The question specifies that the protein molecule is "folded back on itself." This description aligns with the **secondary structure** of proteins.
- The secondary structure includes formations such as alpha helices and beta sheets, which occur due to the folding of the linear polypeptide chain.

3. **Understanding the Bonds**:
- The folds or coils in the secondary structure are stabilized by **hydrogen bonds**. These bonds form between the hydrogen atom of one amino acid and the oxygen atom of another, contributing to the overall stability of the structure.

4. **Final Answer**:
- Therefore, the correct answers to fill in the blanks are:
- The first blank is **secondary** structure.
- The second blank is **hydrogen bonds**.

### Complete Answer:
At some points, a protein molecule may be folded back on itself. This is called **secondary** structure, and folds or coils are held together in place by **hydrogen bonds**.

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