EcoRI always cut DNA molecules at a particular point by recognizing a specific sequence between :

Options

A. G and A
B. T and C
C. A and A
D. T and T

Answer

To solve the question regarding EcoRI and its specific cutting site in DNA, we will follow these steps:

### Step 1: Understand the Role of EcoRI
EcoRI is a type of restriction endonuclease, which means it is an enzyme that cuts DNA at specific sequences.

**Hint:** Remember that restriction enzymes are crucial for molecular biology techniques, as they allow for the manipulation of DNA.

### Step 2: Identify the Recognition Sequence
EcoRI recognizes a specific palindromic DNA sequence. The sequence recognized by EcoRI is:
5' - GAATTC - 3'
3' - CTTAAG - 5'

**Hint:** Palindromic sequences read the same forwards and backwards on complementary strands.

### Step 3: Determine the Cutting Point
EcoRI cuts between the guanine (G) and adenine (A) nucleotides in the sequence. Specifically, it cleaves the DNA at the following site:
- Between the first G and the first A in the sequence GAATTC.

**Hint:** Look for the specific nucleotides in the recognition sequence to find the cutting point.

### Step 4: Analyze the Options
Now, we can analyze the options provided in the question:
- A) Between guanine and adenine (Correct)
- B) Between thiamine and cytosine (Incorrect)
- C) Between adenine and adenine (Incorrect)
- D) Between thiamine and thiamine (Incorrect)

**Hint:** Cross-reference the cutting point with the options to determine which one matches.

### Step 5: Conclusion
The correct answer is that EcoRI always cuts DNA molecules at a specific point by recognizing a sequence between guanine and adenine.

**Final Answer:** A) Between guanine and adenine.