DNA Replication Practice Worksheet showing the steps of DNA replication with diagrams and questions.

Here is the solution to the DNA replication practice worksheet, explained step by step:

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1. What is happening to the DNA molecule in the figure? (Explain the first step in DNA replication)

> Answer:
> In the first step, called initiation, the DNA double helix is being “unzipped” by an enzyme called helicase. This enzyme breaks the hydrogen bonds between the complementary base pairs (A-T and G-C), separating the two strands of the original DNA molecule. This creates a “replication fork,” where each strand will serve as a template for building a new complementary strand.

> *In the image, you can see the original double-stranded DNA splitting apart into two single strands — this represents the action of helicase.*

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2. What happens to the DNA molecule during the second step of DNA replication?

> Answer:
> The second step is called elongation. During this phase, the enzyme DNA polymerase moves along each separated template strand and adds complementary nucleotides to build a new strand. For example, if the template strand has an ‘A’, DNA polymerase adds a ‘T’; if it has a ‘G’, it adds a ‘C’, and so on. This results in two new DNA molecules, each consisting of one original (parental) strand and one newly synthesized strand — this is known as semi-conservative replication.

> *The image shows small nucleotide pieces (with bases A, T, C, G) being added to each template strand, forming new complementary strands.*

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3. What happens during the third step of DNA replication?

> Answer:
> The third step is called termination. At this stage, DNA polymerase performs a final proofreading function — it checks the newly synthesized strands for any mismatched or incorrect bases and corrects them. After proofreading, the two new DNA molecules rewind into their familiar double-helix structure. Each resulting DNA molecule is identical to the original and contains one old strand and one new strand.

> *The image shows two complete double-stranded DNA molecules, indicating that replication is finished and the DNA has re-formed its helical shape.*

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✔ Summary of the 3 Steps:

1. Initiation — Helicase unzips DNA.
2. Elongation — DNA polymerase builds new complementary strands.
3. Termination — DNA polymerase proofreads and fixes errors; DNA rewinds into double helix.

This process ensures accurate copying of genetic information before cell division.

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