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 and disease.

DNA Repair

In this video, we're going to begin our lesson on DNA repair. And so it turns out that DNA replication is not always a perfect process. And so most of the time, DNA replication works exactly as it's supposed to, but occasionally DNA replication will not work perfectly, and it will create errors. And so base pairing errors can occur during DNA replication. And so, for example, we know that A's or adenines are normally supposed to be paired up with T's or thymines. But if there's a base pairing error that occurs, then this A might be base-paired with a C or cytosine instead of being base-paired with the T thymine like what it's supposed to be. And so 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. Now unrepaired errors can actually result in permanent mutations, and these permanent mutations in the DNA can actually lead to diseases like cancer, for example.

And so 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. And so 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 over to the big boss over here. The boss is reading through the resume and he says, says here that you're a professional booger. And this guy's trying to clear it up. He's like, oops, I meant blogger. And so 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. And so mutations, these unrepaired errors in the DNA kind of resemble typos in a resume. And so they can actually significantly change the end result of the product that's supposed to be encoded by the DNA. And so, these unrepaired errors or mutations can lead to diseases like cancer.

And so 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 really 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 of these DNA polymerases 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, they are still possible because 1 in 10,000,000,000 is still possible. Other DNA repair enzymes, on top of the DNA polymerase proofreading, can also be involved with helping to correct errors that may not have been fixed by proofreading. Below in our image, we are showing you a cartoon of a DNA polymerase proofreading the DNA sequence after replication. It says, "Looks like you made a typo here," and this proofreading ability allows for fixing those errors and mistakes in the DNA. Again, that will reduce the error rate to just 1 in 10,000,000,000 base pairs, which is significantly lower and makes mutations due to errors in DNA replication much less likely. This here 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 the error rate of DNA replication without proofreading?

The error rate of DNA replication without proofreading is approximately 1 in 100,000 base pairs. This means that for every 100,000 base pairs replicated, one error is likely to occur. While this might seem like a low error rate, considering the vast amount of DNA in an organism and the frequency of DNA replication, these errors can accumulate and potentially lead to mutations and diseases such as cancer.

How does DNA polymerase proofreading reduce the error rate in DNA replication?

DNA polymerase proofreading significantly reduces the error rate in DNA replication by identifying and correcting mismatched base pairs during the replication process. This proofreading ability decreases the error rate from 1 in 100,000 base pairs to 1 in 10,000,000,000 base pairs. The enzyme detects errors and excises the incorrect nucleotide, replacing it with the correct one, thereby ensuring the accuracy and integrity of the genetic information.

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 alter the function of genes and proteins, potentially leading to various diseases, including cancer. Mutations can disrupt normal cellular processes, cause uncontrolled cell growth, and result in the development of tumors. Therefore, efficient DNA repair mechanisms are crucial for maintaining genetic stability and preventing disease.

What role do DNA repair enzymes play in maintaining genetic integrity?

DNA repair enzymes play a critical role in maintaining genetic integrity by correcting errors that escape the proofreading activity of DNA polymerases. These enzymes detect and repair mismatches, insertions, deletions, and other types of DNA damage. By fixing these errors, DNA repair enzymes help prevent mutations, ensuring the accurate transmission of genetic information and protecting against diseases such as cancer.

How do mutations caused by DNA replication errors lead to cancer?

Mutations caused by DNA replication errors can lead to cancer by disrupting the normal regulation of cell growth and division. If a mutation occurs in a gene that controls cell cycle checkpoints, apoptosis, or DNA repair, it can result in uncontrolled cell proliferation. Accumulation of such mutations can transform normal cells into cancerous cells, leading to the formation of tumors and the spread of cancer throughout the body.