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PCR was used to amplify a region of DNA - Scottish Highers Human Biology - Question 3 - 2023

Question 3

PCR was used to amplify a region of DNA. After 5 cycles 32 copies were present. Calculate the number of additional copies present after 4 further cycles.

Worked Solution & Example Answer:PCR was used to amplify a region of DNA - Scottish Highers Human Biology - Question 3 - 2023

Step 1

Calculate the number of copies after 5 cycles

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Answer

In PCR, the number of copies can be calculated using the formula: $N = N_0 imes 2^n$ where:

$N$ is the final number of copies,
$N_0$ is the initial number of copies,
$n$ is the number of cycles.

After 5 cycles, we know $N = 32$ . To find the initial number of copies ( $N_0$ ), we can rearrange the formula: $N_0 = \frac{N}{2^n}$ Substituting in the values gives us: $N_0 = \frac{32}{2^5} = \frac{32}{32} = 1$ Therefore, there was 1 initial copy before amplification.

Step 2

Calculate the number of copies after 9 cycles

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Answer

Now we want to calculate the number of copies after 9 total cycles (5 + 4). Using the same formula, we have: $N = N_0 \times 2^n$ $N = 1 \times 2^9 = 2^9 = 512$ So, after 9 cycles, there will be 512 copies.

Step 3

Additional copies after 4 more cycles

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Answer

To find the number of additional copies, we subtract the number of copies after 5 cycles from the total number after 9 cycles: $\text{Additional copies} = N(9) - N(5) = 512 - 32 = 480$ Thus, the additional copies present after 4 more cycles are 480.

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