DNA Replication Honors

Summary

DNA replication is a vital process where cells make an exact copy of their DNA. This semi-conservative process involves enzymes like helicase, DNA polymerase, and DNA ligase. The DNA double helix unwinds at the replication fork, and new nucleotides are added to form complementary strands. The leading strand is synthesized continuously, while the lagging strand is made in Okazaki fragments, later joined by DNA ligase. This replication process occurs in the S phase of the cell cycle, ensuring each daughter cell receives identical genetic material for cell division.

Takeaways

• 😀 DNA has a double helix shape, consisting of two long nucleotide chains with a sugar-phosphate backbone on the outside.
• 😀 DNA is anti-parallel, meaning one strand runs in one direction, while the other runs in the opposite direction.
• 😀 DNA replication, also known as DNA synthesis, occurs in the nucleus during the S phase of the cell cycle before mitosis.
• 😀 DNA replication is semi-conservative, meaning each new DNA molecule contains one old template strand and one new strand.
• 😀 The first step in DNA replication is the binding of enzymes to the DNA strand being replicated.
• 😀 Helicase unwinds the DNA double helix, separating the strands to allow for the synthesis of new strands.
• 😀 DNA polymerase adds new nucleotides to the template strand, following base pairing rules to form a complementary strand.
• 😀 The replication bubble is the region where DNA replication begins, containing two replication forks on either side.
• 😀 DNA is synthesized in the 5' to 3' direction, with one strand being made continuously (leading strand) and the other in fragments (lagging strand).
• 😀 Okazaki fragments are short DNA segments on the lagging strand that are later joined together by DNA ligase to form a continuous strand.
• 😀 The three key enzymes involved in DNA replication are helicase (unwinds DNA), DNA polymerase (adds nucleotides), and DNA ligase (joins Okazaki fragments).

Q & A

What is the structure of DNA?

DNA has a double helix shape, often described as a twisted ladder. It consists of two long nucleotide chains with a sugar-phosphate backbone on the outside, and the strands run in opposite (anti-parallel) directions.

Where does DNA replication occur?

DNA replication occurs in the nucleus of the cell, as that is where the DNA is located.

What is meant by semi-conservative replication?

Semi-conservative replication means that each new DNA molecule consists of one original (old) strand and one newly synthesized strand.

What is the role of helicase in DNA replication?

Helicase unwinds the DNA double helix by separating the two strands, providing space for the new strands to be synthesized.

What is the role of DNA polymerase during replication?

DNA polymerase adds new nucleotides to the template strand following the base-pairing rules (A with T, G with C) to synthesize the new DNA strand.

Why is the lagging strand synthesized in Okazaki fragments?

The lagging strand is synthesized in fragments because DNA can only be synthesized in the 5' to 3' direction, and the anti-parallel nature of the strands forces the synthesis to occur in segments.

How are Okazaki fragments joined together?

Okazaki fragments on the lagging strand are joined together by the enzyme DNA ligase, which forms covalent bonds between the fragments.

What is the difference between the leading strand and the lagging strand?

The leading strand is synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized in fragments due to its opposite direction, later joined by DNA ligase.

What happens at the origin of replication?

At the origin of replication, the DNA begins to separate, forming a replication bubble where the helicase unwinds the strands and replication forks are formed for the synthesis of new DNA strands.

Which enzymes are involved in DNA replication, and what are their functions?

The key enzymes involved in DNA replication include helicase (which unwinds the DNA), DNA polymerase (which adds nucleotides to form the new strand), and DNA ligase (which joins Okazaki fragments on the lagging strand).