Which of the following statement is incorrect

Options

A. Prions consist of abnormally folded proteins
B. Viroids lack a protein coat
C. Viruses are obligate parasites
D. Infective constituent in viruses is the protein coat

Explanation

To determine which statement is incorrect among the given options, we can analyze each statement step by step:

### Step 1: Analyze the first statement about prions.
- **Statement**: Prions consist of abnormally folded proteins.
- **Analysis**: This statement is correct. Prions are indeed misfolded proteins that can induce other proteins to misfold, leading to disease.

### Step 2: Analyze the second statement about viroids.
- **Statement**: Viroids lack a protein coat.
- **Analysis**: This statement is also correct. Viroids are small, circular RNA molecules that do not have a protein coat, distinguishing them from viruses.

### Step 3: Analyze the third statement about viruses.
- **Statement**: Viruses are obligate parasites.
- **Analysis**: This statement is correct as well. Viruses can only replicate inside the living cells of a host organism, making them obligate parasites.

### Step 4: Analyze the fourth statement about the infective constituent of viruses.
- **Statement**: The infective constituent in viruses is the protein coat.
- **Analysis**: This statement is incorrect. The infective constituent of viruses is actually their nucleic acid, which can be either DNA or RNA, not the protein coat.

### Conclusion:
After analyzing all the statements, the incorrect statement is:
- **D**: The infective constituent in viruses is the protein coat.

### Final Answer:
The incorrect statement is option D.

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