Problem 9 - Biology: The Dynamic Science

Question

Mismatch repair is the ability: a. to seal Okazaki fragments with ligase into a continual DNA strand. b. of primase to remove the RNA primer and replace it with the correct DNA. c. of some enzymes to sense the insertion of an incorrect nucleotide, remove it, and use a DNA polymerase to insert the correct one. d. to correct mispaired chromosomes in prophase I of meiosis. e. to remove worn-out DNA by telomerase and replace it with newly synthesized nucleotides.

Step-by-Step Solution

Answer

The correct answer is (c). Mismatch repair is the ability of some enzymes to sense the insertion of an incorrect nucleotide, remove it, and use a DNA polymerase to insert the correct one.

Step 1: Understanding the Concept of Mismatch Repair

Mismatch repair is a cellular process used to repair incorrect nucleotides that have been incorporated into DNA. This system recognizes and fixes errors that escape the proofreading activity of DNA polymerase during DNA replication. The incorrect nucleotides are removed and the correct ones are inserted.

Step 2: Analyzing Each Option

Review each provided option and compare it with the concept of mismatch repair: (a) refers to DNA ligase function in joining Okazaki fragments, not mismatch repair. (b) involves the action of primase and is not related to mismatch repair. (c) correctly describes mismatch repair enzymes sensing and correcting incorrect nucleotides. (d) refers to correction of mispairing during meiosis, not mismatch repair. (e) discusses the role of telomerase, which is unrelated to mismatch repair.

Step 3: Identifying the Correct Statement

Compare the definition of mismatch repair with the options given. The statement that matches the definition is the correct answer.

Key Concepts

DNA Replication

DNA replication is a critical process in which the DNA double helix unwinds and creates two identical copies of itself before the cell divides. This process ensures that each new cell has the same genetic information as the parent cell. The replication is performed by enzymes known as DNA polymerases. However, it's not a flawless mechanism, as errors can occur when DNA polymerase incorporates incorrect nucleotides into the new DNA strand.

During replication, unwinding of the double helix is initiated at specific regions known as origins of replication. DNA polymerase then adds nucleotides to a primer sequence, synthesizing the new strand in a 5' to 3' direction. This occurs on the leading strand continuously and on the lagging strand in short fragments called Okazaki fragments, which are later joined by DNA ligase.

DNA Polymerase Proofreading

DNA polymerase is a vital enzyme with an intrinsic proofreading ability that helps maintain the accuracy of DNA replication. This proofreading function is due to the enzyme's 3' to 5' exonuclease activity, which allows it to remove incorrectly paired nucleotides as they are incorporated.

When a DNA polymerase adds a nucleotide that does not correctly base pair with the opposing nucleotide strand, it detects the mistake and excises the wrong nucleotide. The enzyme then inserts the correct nucleotide to maintain the fidelity of the DNA sequence. Despite this proofreading capability, some errors still manage to persist and make it past this checkpoint. These errors are what give rise to the need for further repair mechanisms, like mismatch repair.

Cellular Repair Processes

Cellular repair processes, such as mismatch repair, are crucial for correcting errors that escape the proofreading activity of DNA polymerase. Mismatch repair enzymes recognize the misincorporated nucleotide, excise a short stretch of the DNA strand containing the error, and fill in the gap with the correct nucleotides.

This process is essential for maintaining genome stability and preventing mutations that could lead to diseases, including cancer. The mismatch repair mechanism is just one of the several cellular repair systems. Others include base excision repair and nucleotide excision repair, both of which address different types of DNA damage.