What is meant by the term semiconservative replication? What are the functions of DNA Pol I and III, helicase, and primase? How does a leading strand differ from a lagging strand?

Step 1: Define the Problem

Identify the key components of the question:

• Definition of semiconservative replication
• Functions of DNA Pol I, DNA Pol III, helicase, and primase
• Differences between leading and lagging strands

Step 2: Break Down the Problem

1. Explain semiconservative replication.
2. Describe the functions of the enzymes involved in DNA replication.
3. Compare the leading and lagging strands.

Step 3: Apply Relevant Concepts

Semiconservative Replication

• Definition: Semiconservative replication is the process by which DNA is replicated in cells, resulting in two DNA molecules, each with one original strand and one newly synthesized strand.

Functions of Enzymes

• DNA Polymerase I (Pol I): Involved in removing RNA primers and replacing them with DNA nucleotides. It also has exonuclease activity for proofreading.
• DNA Polymerase III (Pol III): The primary enzyme responsible for DNA synthesis, adding nucleotides to the growing DNA strand in a 5' to 3' direction.
• Helicase: Unwinds the DNA double helix at the replication fork to allow the two strands to be copied.
• Primase: Synthesizes short RNA primers that provide a starting point for DNA synthesis by DNA polymerases.

Leading vs. Lagging Strand

• Leading Strand: Synthesized continuously in the direction of the replication fork movement.
• Lagging Strand: Synthesized discontinuously in short segments called Okazaki fragments, which are later joined together.

Step 4: Analysis, Verify and Summarize

• Semiconservative Replication: Ensures genetic consistency across generations by preserving one original DNA strand in each daughter molecule.
• Enzyme Functions: Each enzyme plays a crucial role in ensuring accurate and efficient DNA replication.
• Strand Differences: The leading strand allows for continuous synthesis, while the lagging strand requires multiple initiation events and fragment joining.

Final Answer

Semiconservative replication involves creating two DNA molecules, each with one old and one new strand. DNA Pol I removes RNA primers and fills gaps with DNA, DNA Pol III synthesizes new DNA strands, helicase unwinds the DNA, and primase lays down RNA primers. The leading strand is synthesized continuously, while the lagging strand is synthesized in Okazaki fragments.