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Mobile App Chapter 10: Problem 23
Single-stranded regions of DNA are attacked by nucleases in the cell, yet portions of DNA are in a single-stranded form during the replication process. Explain.
Short Answer
Expert verified
SSBs protect ssDNA during replication from nuclease degradation.
Step by step solution
01
Understand DNA Structure
DNA typically exists as a double helix with two complementary strands that protect it from nucleases.
02
Initiate DNA Replication
During replication, the DNA double helix is unwound by helicase to create two single-stranded templates for synthesis.
03
Function of Single-Stranded Binding Proteins (SSBs)
SSBs bind to single-stranded DNA (ssDNA) during replication to prevent nucleases from degrading it and to avoid secondary structure formation.
04
Role of Nucleases
Nucleases degrade exposed ssDNA to protect the integrity of the genetic material. However, during replication, ssDNA is temporarily formed and is protected by replication machinery.
05
Conclusion
While ssDNA is vulnerable, it is protected by proteins and enzymes during replication, preventing nuclease degradation.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
DNA Structure
DNA, or deoxyribonucleic acid, is the molecule that carries the genetic instructions for life. It has a special structure known as a double helix. Imagine a twisted ladder, where the sides of the ladder are made up of sugar and phosphate molecules, and the rungs are pairs of nitrogenous bases.
The double helix structure is stable and protects the genetic code from damage.
Each base pair consists of a purine (adenine or guanine) and a pyrimidine (thymine or cytosine), connected by hydrogen bonds. This complementary base pairing is central to DNA replication.
The double helix structure is stable and protects the genetic code from damage.
Each base pair consists of a purine (adenine or guanine) and a pyrimidine (thymine or cytosine), connected by hydrogen bonds. This complementary base pairing is central to DNA replication.
Single-Stranded Binding Proteins (SSBs)
Single-Stranded Binding Proteins (SSBs) are crucial for DNA replication. During the replication process, the double helix is unwound, exposing single strands of DNA.
These single strands are unstable and prone to attack by nucleases, but SSBs come to the rescue.
SSBs bind to the single-stranded DNA (ssDNA), stabilizing it and preventing the formation of secondary structures that could interfere with replication.
These single strands are unstable and prone to attack by nucleases, but SSBs come to the rescue.
SSBs bind to the single-stranded DNA (ssDNA), stabilizing it and preventing the formation of secondary structures that could interfere with replication.
- SSBs keep ssDNA straight and accessible for replication enzymes.
- They help prevent premature re-annealing of the DNA strands.
- SSBs play a role in signaling other proteins to the replication fork.
Nucleases
Nucleases are enzymes that cut DNA strands by breaking the phosphodiester bonds between nucleotides. They play a role in protecting the cell by degrading foreign DNA and faulty sections of its own DNA.
In the context of replication, nucleases are a double-edged sword. They can degrade single-stranded DNA, potentially causing damage.
However, the cell's replication machinery has evolved ways to protect ssDNA from nucleases during replication, primarily through the action of SSBs and other protective measures.
This balance ensures the integrity and continuity of the genetic information during cell division.
In the context of replication, nucleases are a double-edged sword. They can degrade single-stranded DNA, potentially causing damage.
However, the cell's replication machinery has evolved ways to protect ssDNA from nucleases during replication, primarily through the action of SSBs and other protective measures.
This balance ensures the integrity and continuity of the genetic information during cell division.
Helicase
Helicase is an enzyme that unwinds the DNA double helix ahead of the replication fork. This unwinding is necessary for the replication machinery to access the DNA template for synthesizing new strands.
By breaking the hydrogen bonds between base pairs, helicase separates the two strands of DNA, creating a forked structure.
By breaking the hydrogen bonds between base pairs, helicase separates the two strands of DNA, creating a forked structure.
- Helicase requires energy, which it obtains from the hydrolysis of ATP (adenosine triphosphate).
- Efficient function of helicase is paramount for the replication process.
- Malfunctions in helicase activity can lead to replication stress and genomic instability.
Replication Machinery
DNA replication is a complex process involving a host of specialized proteins and enzymes, collectively referred to as the replication machinery. This includes DNA polymerases, primase, ligase, and various accessory proteins.
DNA polymerases synthesize new DNA strands by adding nucleotides complementary to the template strand.
Primase synthesizes short RNA primers necessary for DNA polymerases to begin synthesis.
Ligase seals nicks in the DNA backbone, ensuring a continuous double-stranded DNA molecule.
DNA polymerases synthesize new DNA strands by adding nucleotides complementary to the template strand.
Primase synthesizes short RNA primers necessary for DNA polymerases to begin synthesis.
Ligase seals nicks in the DNA backbone, ensuring a continuous double-stranded DNA molecule.
- This machinery coordinates to ensure accurate, fast, and faithful replication of the DNA.
- SSBs, helicase, and other proteins work in concert to protect and replicate DNA efficiently.
