Which of the following statements 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

Answer

To determine which statement is incorrect regarding viruses, prions, and viroids, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Understanding the Components of Viruses**:
- Viruses consist of two main components: a protein coat (capsid) and genetic material (either DNA or RNA). They do not have both types of genetic material; it is always one or the other.

2. **Analyzing the First Statement**:
- The first statement claims that "prions consist of abnormally folded proteins."
- This statement is **correct** because prions are indeed misfolded proteins that can cause diseases.

3. **Analyzing the Second Statement**:
- The second statement states that "viroids lack a protein coat."
- This statement is also **correct**. Viroids are composed solely of a short strand of RNA and do not have a protein coat.

4. **Analyzing the Third Statement**:
- The third statement mentions that "viruses are obligate parasites."
- This statement is **correct** as viruses cannot reproduce or carry out metabolic processes without a host cell.

5. **Analyzing the Fourth Statement**:
- The fourth statement claims that "the infective constituent in the virus is a protein coat."
- This statement is **incorrect**. The infective component of a virus is its genetic material (either DNA or RNA), not the protein coat.

### Conclusion:
- The incorrect statement is **Option 4**: "the infective constituent in the virus is a protein coat."