Untitled Quiz

Questions and Answers

What is the beginning of DNA replication?

DNA strands are synthesized continuously.

Only two origins of replication are present.

Only one strand of DNA is separated.

Two strands of DNA are separated, opening a replication bubble. (correct)

What is the role of DNA polymerase I?

Removes RNA primer and replaces it with newly synthesized DNA.

What does DNA polymerase III do?

Adds nucleotides in the 5' to 3' direction.

What is the function of helicase?

Opens the DNA helix by breaking hydrogen bonds between nitrogenous bases. Signup and view all the answers

What does ligase do in DNA replication?

Seals gaps between Okazaki fragments to create a continuous strand. Signup and view all the answers

What is the role of primase in DNA replication?

Synthesizes RNA primers needed to start replication. Signup and view all the answers

What is the purpose of the sliding clamp?

Helps hold the DNA polymerase in place when nucleotides are being added. Signup and view all the answers

How does topoisomerase help during DNA replication?

Relieves stress on DNA when unwinding by causing breaks and resealing it. Signup and view all the answers

What is the function of single-strand binding proteins (SSB)?

Binds to single-stranded DNA to prevent it from rewinding. Signup and view all the answers

What is a replication fork?

A Y-shaped region where DNA strands are elongating. Signup and view all the answers

What is the rate of elongation in bacteria?

500 nt/s. Signup and view all the answers

What is a leading strand?

Strand synthesized continuously in the direction of the replication fork (5' to 3'). Signup and view all the answers

What characterizes a lagging strand?

Replicated in short fragments and away from the replication fork (3' to 5'). Signup and view all the answers

What are Okazaki fragments?

DNA fragments synthesized in short stretches by the lagging strand. Signup and view all the answers

List the steps of DNA replication.

<ol> <li>DNA unwinds at the origin of replication. 2. Helicase opens up the DNA, forming replication forks. 3. SSB proteins coat the DNA around the replication fork to prevent rewinding. 4. Topoisomerase binds at the region ahead of the replication fork to prevent supercoiling. 5. Primase synthesizes RNA primers. 6. DNA polymerase adds nucleotides. 7. Both lagging and leading strand elongation continues. 8. RNA primers are removed. 9. Gaps are filled by DNA polymerase. 10. DNA ligase seals gaps between DNA fragments.</li> </ol> Signup and view all the answers

Study Notes

DNA Replication Overview

Initiation occurs at a single origin of replication, forming a replication "bubble" as DNA strands separate.
A replication fork is created, resembling a Y-shape, where elongation of DNA strands happens.

Key Enzymes and Proteins

Helicase: Unzips the DNA helix by breaking hydrogen bonds between nitrogenous bases.
DNA polymerase III: Primary enzyme responsible for adding nucleotides in the 5' to 3' direction during replication.
DNA polymerase I: Replaces RNA primers with newly synthesized DNA segments after initial replication.
Primase: Synthesizes RNA primers that provide a starting point for DNA synthesis.
Ligase: Seals gaps between Okazaki fragments on the lagging strand, forming a continuous DNA molecule.
Topoisomerase: Alleviates tension in the DNA helix by creating temporary breaks before resealing the strands.
Single-strand binding proteins (SSB): Attach to exposed single-stranded DNA to prevent it from rejoining.

Strands and Their Characteristics

Leading strand: Synthesized continuously toward the replication fork in the 5' to 3' direction.
Lagging strand: Discontinuously synthesized away from the replication fork in 3' to 5' direction, creating Okazaki fragments.

Okazaki Fragments

Short DNA segments synthesized on the lagging strand; necessary due to the nature of DNA's antiparallel structure.

Rate of Elongation

Bacterial DNA elongates at approximately 500 nucleotides per second.
Human cells replicate DNA at a rate of about 50 nucleotides per second.

DNA Replication Process Steps

DNA unwinds at the origin, helicase separates strands, and SSBs prevent rewinding.
Topoisomerase prevents supercoiling ahead of the replication fork.
Primase lays down RNA primers, allowing DNA polymerase to start adding nucleotides.
Following elongation, RNA primers are removed, gaps are filled with DNA, and ligase seals the fragments.