Introduction to DNA Repair: Study with Video Lessons, Practice Problems & Examples

DNA repair is crucial for maintaining cellular integrity, as even minor mutations can significantly impact cell function. Cells utilize various conserved mechanisms to repair DNA, categorized into four groups: nucleotide mismatch repair, damaged DNA repair, thymine dimer repair, and extensive damage repair. Key processes include DNA polymerase proofreading and mismatch repair for nucleotide mismatches, base excision repair for damaged DNA, nucleotide excision repair and photoreactivation for thymine dimers, and SOS repair for extensive damage. Understanding these mechanisms is essential for grasping cellular resilience and genetic stability.

Introduction to DNA Repair

In this video, we're going to begin our introduction to DNA repair. It's important to note that even small mutations to the DNA within a cell can have tremendous effects on the life of a cell. However, thankfully, there are multiple DNA repair mechanisms within a cell that are conserved across all domains of life. Moving forward in our course, we're going to talk about several different types of DNA repair mechanisms. We're showing you an image right here that represents our map of the lesson on DNA repair as we move forward in our course. You can use this map, to help guide you through our lesson as we discuss DNA repair mechanisms. Notice here we have at the top DNA repair mechanisms, and we've grouped these DNA repair mechanisms into four groups: those that repair nucleotide mismatches, those that repair damaged DNA, those that repair what are known as Thymine Dimers, and those for repairing many mutations, extensive damage. Moving forward, we're going to be following the leftmost branches first, and then we'll zoom out and continue to follow the path as you see here. First, we're going to talk about DNA repair mechanisms that repair nucleotide mismatches. This includes DNA Polymerase proofreading, and it also includes mismatch repair. After we cover those, we'll move on to talk about repairing damaged DNA, and this is going to be specifically referring to base excision repair. Then we'll talk about repairing Thymine Dimers, and this is going to include nucleotide excision repair. We'll then discuss photo reactivation. After that, we'll talk about repairing many mutations, repairing extensive damage and this is going to be followed by SOS repair. This is a map of our lesson moving forward and we'll get to talk about all of these different DNA repair mechanisms in their own individual separate videos, starting with the DNA polymerase proofreading. So, I'll see you all in our next video to talk more about that.

Based on the map above, if the cell needed to repair a nucleotide mismatch mutation, which form of repair could it use?

• A. Nucleotide excision repair.
• B. DNA Polymerase proofreading.
• C. Mismatch repair.
• D. Photoreactivation.
• E. A and D.
• F. B and C.

Based on the map above, if one of the bases in a strand of DNA is damaged and needs to be replaced, what mechanism will the cell use to repair the DNA?

• A. Mismatch repair.
• B. Nucleotide excision repair.
• C. Base excision repair.
• D. Photoreactivation.

Here’s what students ask on this topic:

What are the main types of DNA repair mechanisms?

The main types of DNA repair mechanisms are categorized into four groups: nucleotide mismatch repair, damaged DNA repair, thymine dimer repair, and extensive damage repair. Nucleotide mismatch repair includes DNA polymerase proofreading and mismatch repair. Damaged DNA repair primarily involves base excision repair. Thymine dimer repair includes nucleotide excision repair and photoreactivation. Extensive damage repair is managed by the SOS repair system. These mechanisms are crucial for maintaining genetic stability and cellular integrity by correcting various types of DNA damage.

How does DNA polymerase proofreading work in DNA repair?

DNA polymerase proofreading is a critical mechanism for correcting nucleotide mismatches during DNA replication. As DNA polymerase synthesizes a new DNA strand, it continuously checks each newly added nucleotide. If an incorrect nucleotide is incorporated, the enzyme's 3' to 5' exonuclease activity removes the mismatched nucleotide. The polymerase then replaces it with the correct nucleotide, ensuring high fidelity in DNA replication. This proofreading function significantly reduces the error rate, maintaining genetic stability.

What is base excision repair and how does it function?

Base excision repair (BER) is a mechanism that corrects damaged DNA bases resulting from oxidation, alkylation, or deamination. The process begins with a DNA glycosylase enzyme recognizing and removing the damaged base, creating an abasic site. An AP endonuclease then cleaves the DNA backbone at this site. DNA polymerase fills in the gap with the correct nucleotide, and DNA ligase seals the nick, restoring the DNA to its original state. BER is essential for maintaining DNA integrity and preventing mutations.

What role does nucleotide excision repair play in fixing thymine dimers?

Nucleotide excision repair (NER) is crucial for repairing thymine dimers, which are covalent linkages between adjacent thymine bases caused by UV radiation. NER involves several steps: recognition of the dimer, unwinding of the DNA around the lesion by helicases, excision of a short single-stranded DNA segment containing the dimer by endonucleases, synthesis of the correct DNA sequence by DNA polymerase, and sealing of the new DNA strand by DNA ligase. This process restores the DNA to its undamaged state, preventing mutations and maintaining genomic stability.

What is the SOS repair system and when is it activated?

The SOS repair system is a global response to extensive DNA damage that threatens cell survival. It is activated when the DNA damage is too severe for other repair mechanisms to handle. The system involves the induction of several genes, including those encoding error-prone DNA polymerases, which can bypass lesions but often introduce mutations. The SOS response is regulated by the RecA protein, which senses DNA damage and promotes the autocleavage of the LexA repressor, leading to the expression of SOS genes. While the SOS repair system can save the cell, it increases the risk of mutations.