DNA Repair - Online Tutor, Practice Problems & Exam Prep

DNA replication can introduce errors, with a base pairing error rate of 1 in 100,000 base pairs, potentially leading to mutations and diseases like cancer. DNA polymerases possess proofreading abilities that reduce this error rate to 1 in 10,000,000,000 base pairs. Additional DNA repair enzymes further correct any remaining errors, ensuring the integrity of genetic information. Understanding these mechanisms is crucial for grasping how mutations occur and their implications for health.

DNA Repair

In this video, we're going to begin our lesson on DNA repair. It turns out that DNA replication is not always a perfect process. Most of the time DNA replication works exactly as it's supposed to, but occasionally it will not work perfectly, creating errors. Base pairing errors can occur during DNA replication. For example, we know that adenines (A) are normally supposed to be paired up with thymines (T).

But if there's a base pairing error that occurs, then an A might be base paired with a cytosine (C) instead of being base paired with the T (thymine) like what it's supposed to be. These base pairing errors can occur, and these errors occur 1 out of every 100,000 base pairs, which at first glance might seem like a really low error rate, only one error out of 100,000 base pairs, but it's actually a relatively high error rate considering that there's a lot of DNA and the DNA replication needs to occur often. Unrepaired errors can actually result in permanent mutations, and these permanent mutations in the DNA can actually lead to diseases like cancer, for example. Down below in our image, in our example image, we're showing you how these DNA errors can kind of resemble typos in a resume. In this cartoon that we're showing you down below, this guy over here is coming in for an interview for a job position, and he hands his resume to the big boss over here.

The boss is reading through the resume, and he says, "It says here that you're a professional bugger." This guy is trying to clear it up. He's like, "Oops, I meant blogger." That's a typo that's in the resume. And that is going to greatly affect this guy's chances of landing this job position.

Mutations, these unrepaired errors in the DNA kind of resemble typos in a resume. They can significantly change the end result of the product that's supposed to be encoded by the DNA. These unrepaired errors or mutations can lead to diseases like cancer. This here concludes our brief introduction to DNA repair, and we'll be able to talk a little bit more as we move forward in our course. So I'll see you in our next video.

DNA Proofreading & Repair Enzymes

In this video, we're going to briefly introduce DNA proofreading and DNA repair enzymes. DNA polymerases actually have a proofreading ability. This proofreading ability is just an ability that these DNA polymerases have to find and fix many of the errors or mistakes that might occur during DNA replication. The proofreading ability that these DNA polymerases have actually allows them to significantly reduce the error rate from 1 in 100,000 to just 1 in 10,000,000,000 base pairs, making mutations a lot less likely due to mistakes with DNA polymerases. However, mutations are still possible because 1 in 10,000,000,000 is still a possibility.

Other DNA repair enzymes, on top of the DNA polymerase proofreading, can also be involved in helping to correct errors that may not have been fixed by proofreading. Below in our image, we're showing you a little cartoon of a DNA polymerase proofreading the DNA sequence after replication. It says, "Looks like you made a typo here," and what this proofreading ability allows for is fixing those errors and mistakes in the DNA. Again, that will reduce the error rate to just 1⁢in⁢10000000000 base pairs, which is significantly lower and makes mutations due to errors in DNA replication much less likely. This concludes our brief introduction to DNA proofreading ability and repair enzymes that can also help reduce error rates.

We'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

Researchers found a strain of E. coli bacteria that had mutation rates one hundred times higher than normal. Which of the following statements correctly describes the most likely cause of these mutations?

• A. The single-stranded binding proteins were malfunctioning during DNA replication.
• B. There were one or more mutations in the RNA primer.
• C. The proofreading mechanism of DNA polymerase was malfunctioning.
• D. The DNA polymerase was unable to add bases to the 3′ end of the growing DNA strand.

Here’s what students ask on this topic:

What is DNA proofreading and how does it reduce mutation rates?

DNA proofreading is a mechanism by which DNA polymerases correct errors that occur during DNA replication. These enzymes have the ability to identify and fix mismatched base pairs, significantly reducing the error rate. Initially, the error rate is about 1 in 100,000 base pairs, but with proofreading, it drops to 1 in 10,000,000,000 base pairs. This drastic reduction makes mutations due to replication errors much less likely, thereby maintaining the integrity of genetic information and reducing the risk of diseases like cancer.

What are the consequences of unrepaired DNA replication errors?

Unrepaired DNA replication errors can lead to permanent mutations in the genetic code. These mutations can significantly alter the function of genes, potentially leading to various diseases, including cancer. For example, a base pairing error where adenine (A) is incorrectly paired with cytosine (C) instead of thymine (T) can result in a faulty protein being produced. Over time, the accumulation of such mutations can disrupt normal cellular functions and lead to serious health issues.

How do DNA repair enzymes complement the proofreading function of DNA polymerases?

DNA repair enzymes provide an additional layer of error correction beyond the proofreading function of DNA polymerases. While DNA polymerases can correct many errors during replication, some mistakes may still slip through. DNA repair enzymes can identify and fix these remaining errors, further ensuring the accuracy of the genetic information. This multi-tiered approach helps maintain the low mutation rate and protects against genetic diseases.

Why is understanding DNA repair mechanisms important for health?

Understanding DNA repair mechanisms is crucial for health because it helps us comprehend how genetic mutations occur and their potential consequences. Effective DNA repair processes are essential for preventing mutations that can lead to diseases like cancer. By studying these mechanisms, researchers can develop targeted therapies and preventive measures to combat genetic disorders, ultimately improving health outcomes and advancing medical science.

What is the error rate of DNA replication before and after proofreading?

Before proofreading, the error rate of DNA replication is approximately 1 in 100,000 base pairs. After the proofreading function of DNA polymerases is applied, this error rate is significantly reduced to about 1 in 10,000,000,000 base pairs. This substantial decrease in errors helps ensure the accuracy of genetic information and reduces the likelihood of mutations that could lead to diseases.