Which among the following statements are correct ?
(i) A – T rich region of DNA denature at low temperature and are less stable than G – C rich regions.
(ii) RNA is more stable than DNA .
(iii) SNP are present at about 1 billion locations in humans.
(iv) DNA polymerase I have both 5' `rarr` 3' and `3' rarr5'` exonuclease activity.
(v) Rifampicin inhibits RNA synthesis by inhibiting RNA polymerase.

Options

A. (i) , (iii) and (iv)
B. (i), (ii) and (v)
C. (i) , (iv) and (v)
D. (ii) , (iii) and (v)

Answer

To determine which statements are correct, let's analyze each statement one by one:

### Step 1: Analyze Statement (i)
**Statement (i):** A – T rich region of DNA denature at low temperature and are less stable than G – C rich regions.

- **Analysis:** This statement is correct. A-T pairs are held together by two hydrogen bonds, while G-C pairs are held together by three hydrogen bonds. Therefore, A-T rich regions are less stable and denature at lower temperatures compared to G-C rich regions.

### Step 2: Analyze Statement (ii)
**Statement (ii):** RNA is more stable than DNA.

- **Analysis:** This statement is incorrect. RNA is generally less stable than DNA due to the presence of a hydroxyl group (-OH) on the 2' carbon of the ribose sugar in RNA, making it more reactive and prone to hydrolysis. DNA, with its deoxyribose sugar, is more stable.

### Step 3: Analyze Statement (iii)
**Statement (iii):** SNPs are present at about 1 billion locations in humans.

- **Analysis:** This statement is incorrect. Single Nucleotide Polymorphisms (SNPs) are estimated to be present at about 1.4 million locations in the human genome, not 1 billion.

### Step 4: Analyze Statement (iv)
**Statement (iv):** DNA polymerase I has both 5' → 3' and 3' → 5' exonuclease activity.

- **Analysis:** This statement is correct. DNA polymerase I has exonuclease activity in both directions. The 3' → 5' exonuclease activity is involved in proofreading, while the 5' → 3' exonuclease activity is involved in removing RNA primers and replacing them with DNA.

### Step 5: Analyze Statement (v)
**Statement (v):** Rifampicin inhibits RNA synthesis by inhibiting RNA polymerase.

- **Analysis:** This statement is correct. Rifampicin is an antibiotic that inhibits bacterial RNA polymerase, thereby preventing RNA synthesis.

### Conclusion:
The correct statements are:
- (i) A – T rich region of DNA denature at low temperature and are less stable than G – C rich regions.
- (iv) DNA polymerase I has both 5' → 3' and 3' → 5' exonuclease activity.
- (v) Rifampicin inhibits RNA synthesis by inhibiting RNA polymerase.

Thus, the correct statements are (i), (iv), and (v).

### Final Answer:
The correct statements are (i), (iv), and (v).

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