Biology worksheet focusing on DNA replication processes and key enzymes involved.

Problem: Solve the DNA Replication Questions

Below is a detailed explanation and solution for each question related to DNA replication:

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#### 15. What is the first step in the process of DNA replication?
- Answer: The first step in the process of DNA replication is the unwinding or separation of the two strands of the DNA double helix.
- Explanation: This step is facilitated by an enzyme called helicase, which breaks the hydrogen bonds between the complementary base pairs (A-T and C-G) in the DNA double helix. This unwinding creates a replication fork, where the two strands are separated and serve as templates for new DNA synthesis.

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#### 16. Which enzyme is responsible for "unzipping" the DNA double helix?
- Answer: The enzyme responsible for "unzipping" the DNA double helix is helicase.
- Explanation: Helicase acts at the replication fork, breaking the hydrogen bonds between the complementary base pairs. This action separates the two strands of DNA, allowing them to serve as templates for new DNA synthesis.

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#### 17. Which enzyme is responsible for facilitating the hydrogen bonding between nucleotides in a new DNA molecule?
- Answer: The enzyme responsible for facilitating the hydrogen bonding between nucleotides in a new DNA molecule is DNA polymerase.
- Explanation: DNA polymerase adds complementary nucleotides to the template strand based on the rules of base pairing (A with T, C with G). It ensures that the newly synthesized strand forms correct hydrogen bonds with the template strand.

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#### 18. Which enzyme is responsible for creating the covalent bonds that connect the sugar-phosphate backbone of the new DNA molecules?
- Answer: The enzyme responsible for creating the covalent bonds that connect the sugar-phosphate backbone of the new DNA molecules is DNA ligase.
- Explanation: During DNA replication, short segments of DNA called Okazaki fragments are synthesized on the lagging strand. DNA ligase connects these fragments by forming covalent bonds between the phosphate and sugar groups of adjacent nucleotides, completing the sugar-phosphate backbone.

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#### 19. If the sequence of one single strand of DNA is C-A-A-G-T-A-G-G-C-T, what is the sequence of the complementary strand?
- Answer: The sequence of the complementary strand is G-T-T-C-A-T-C-C-G-A-G.
- Explanation: The base-pairing rules for DNA are:
- Adenine (A) pairs with Thymine (T).
- Cytosine (C) pairs with Guanine (G).

Given the sequence of the template strand: C-A-A-G-T-A-G-G-C-T, we can determine the complementary strand by pairing each base with its complement:
- C → G
- A → T
- A → T
- G → C
- T → A
- A → T
- G → C
- G → C
- C → G
- T → A

Therefore, the complementary strand is G-T-T-C-A-T-C-C-G-A-G.

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#### 20. Describe the origin of each strand of the new double helices created after DNA replication.
- Answer: After DNA replication, each new double helix consists of one original parental strand and one newly synthesized daughter strand.
- Explanation: DNA replication is semi-conservative, meaning that each new DNA molecule retains one strand from the original DNA molecule (the parental strand) and one newly synthesized strand (the daughter strand). This ensures that genetic information is accurately passed on to the next generation of cells.

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#### 21. Why is DNA replication important to the growth and development of a multi-cellular organism?
- Answer: DNA replication is crucial for the growth and development of a multi-cellular organism because it ensures that each new cell receives an exact copy of the genetic material from the parent cell. This process is essential for:
1. Cell Division: During mitosis, DNA replication allows each daughter cell to receive a complete set of chromosomes, ensuring genetic continuity.
2. Development: As cells divide and differentiate, accurate DNA replication ensures that all cells in the organism have the same genetic information, which is necessary for proper development and function.
3. Repair and Maintenance: In some cases, DNA replication is involved in repairing damaged DNA, maintaining the integrity of the genome.

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#### 22. List the 3 basic steps of DNA replication:
- Answer:
a. Unwinding/Unzipping: The DNA double helix is separated into two single strands by helicase.
b. Synthesis of New Strands: DNA polymerase synthesizes new complementary strands using the original strands as templates.
c. Sealing: DNA ligase seals the gaps between Okazaki fragments on the lagging strand, completing the sugar-phosphate backbone.

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Final Answers:

15. The first step is the unwinding/separation of the two strands of the DNA double helix.
16. Helicase
17. DNA polymerase
18. DNA ligase
19. G-T-T-C-A-T-C-C-G-A-G
20. Each new double helix consists of one original parental strand and one newly synthesized daughter strand.
21. DNA replication ensures accurate transmission of genetic information during cell division, supporting growth, development, and repair in multi-cellular organisms.
22.
a. Unwinding/Unzipping
b. Synthesis of New Strands
c. Sealing

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Final Answer Box:

\boxed{
\begin{aligned}
&15. \text{Unwinding/separation of the two strands of the DNA double helix.} \\
&16. \text{Helicase} \\
&17. \text{DNA polymerase} \\
&18. \text{DNA ligase} \\
&19. \text{G-T-T-C-A-T-C-C-G-A-G} \\
&20. \text{Each new double helix consists of one original parental strand and one newly synthesized daughter strand.} \\
&21. \text{Ensures accurate transmission of genetic information during cell division, supporting growth, development, and repair.} \\
&22. \text{a. Unwinding/Unzipping, b. Synthesis of New Strands, c. Sealing} \\
\end{aligned}
}