A DNA segment has 75 cytosine and 40 thymine nucleotides. What shall be the total number of phosphates in the DNA segment?

Options

A. 115
B. 230
C. 75
D. 220

Answer

To determine the total number of phosphates in a DNA segment that contains 75 cytosine (C) and 40 thymine (T) nucleotides, we can follow these steps:

### Step 1: Understand the Structure of DNA
DNA is made up of nucleotides, and each nucleotide consists of three components: a phosphate group, a sugar (deoxyribose), and a nitrogenous base (adenine, thymine, cytosine, or guanine). Each nucleotide has one phosphate group.

### Step 2: Count the Total Number of Nucleotides
In this DNA segment, we have:
- 75 cytosine nucleotides
- 40 thymine nucleotides

To find the total number of nucleotides, we need to add the number of cytosine and thymine nucleotides together.

Total nucleotides = Number of cytosine + Number of thymine
Total nucleotides = 75 + 40 = 115

### Step 3: Determine the Number of Phosphates
Since each nucleotide contains one phosphate group, the total number of phosphates in the DNA segment is equal to the total number of nucleotides.

Total phosphates = Total nucleotides = 115

### Step 4: Consider the Double-Stranded Nature of DNA
DNA is double-stranded, meaning that for each nucleotide in one strand, there is a complementary nucleotide in the other strand. However, the question specifically asks for the total number of phosphates in the DNA segment, which refers to the number of phosphates present in one strand.

Thus, the answer remains 115 phosphates for the segment.

### Step 5: Conclusion
The total number of phosphates in the DNA segment is 115.

### Final Answer
The total number of phosphates in the DNA segment is **115**.

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