Ch. 11 - DNA Replication and Recombination

Klug - Concepts of Genetics 12th Edition

Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook

Klug 12th Edition

Ch. 11 - DNA Replication and Recombination

Problem 27b

Chapter 11, Problem 27b

DNA polymerases in all organisms add only 5' nucleotides to the 3' end of a growing DNA strand, never to the 5' end. One possible reason for this is the fact that most DNA polymerases have a proofreading function that would not be energetically possible if DNA synthesis occurred in the 3' to 5' direction.
Consider the information in your sketch and speculate as to why proofreading would be problematic.

Verified step by step guidance

Understand the directionality of DNA synthesis: DNA polymerases synthesize DNA in the 5' to 3' direction by adding nucleotides to the 3' hydroxyl (-OH) group of the growing strand. This directionality is crucial for the mechanism of DNA replication.

Recognize the role of proofreading: DNA polymerases have a proofreading function, which involves the removal of incorrectly paired nucleotides using their 3' to 5' exonuclease activity. This ensures high fidelity during DNA replication.

Consider the energy requirements for proofreading: In the 5' to 3' synthesis direction, the incoming nucleotide provides the energy for bond formation via its triphosphate group. If synthesis occurred in the 3' to 5' direction, the energy source for proofreading would be unavailable because the triphosphate group would already be part of the growing strand.

Speculate on the consequences of 3' to 5' synthesis: If DNA synthesis occurred in the 3' to 5' direction, removing an incorrect nucleotide during proofreading would leave the strand without a triphosphate group at the 3' end. This would prevent the addition of new nucleotides, halting DNA synthesis entirely.

Conclude why 5' to 3' synthesis is advantageous: The 5' to 3' direction ensures that proofreading can occur without disrupting the energy supply for continued synthesis, maintaining the efficiency and accuracy of DNA replication.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

DNA Polymerase Function

DNA polymerases are enzymes responsible for synthesizing new DNA strands by adding nucleotides to the growing chain. They can only add nucleotides to the 3' end of the strand, which means that DNA synthesis occurs in a 5' to 3' direction. This unidirectional synthesis is crucial for maintaining the integrity and accuracy of DNA replication.

Proofreading Mechanism

Proofreading is a critical function of DNA polymerases that allows them to correct errors during DNA replication. This mechanism involves the enzyme's ability to detect and remove incorrectly paired nucleotides. If DNA synthesis were to occur in the 3' to 5' direction, the proofreading function would be less efficient, as the enzyme would need to backtrack to correct errors, complicating the replication process.

Energetics of DNA Synthesis

The energetics of DNA synthesis refers to the energy requirements for adding nucleotides to a growing DNA strand. The process of adding nucleotides in the 5' to 3' direction is energetically favorable due to the release of pyrophosphate, which drives the reaction forward. If synthesis occurred in the opposite direction, it would require additional energy input to reverse the process, making it less viable for efficient DNA replication.

Recommended video:

Guided course

02:43

Translesion Synthesis

Related Practice

Textbook Question

The genome of D. melanogaster consists of approximately 1.7x10⁸ base pairs. DNA synthesis occurs at a rate of 30 base pairs per second. In the early embryo, the entire genome is replicated in five minutes. How many bidirectional origins of synthesis are required to accomplish this feat?

Textbook Question

Assume a hypothetical organism in which DNA replication is conservative. Design an experiment similar to that of Taylor, Woods, and Hughes that will unequivocally establish this fact. Using the format established in Figure 11.5, draw sister chromatids and illustrate the expected results establishing this mode of replication.

views

Textbook Question

DNA polymerases in all organisms add only 5' nucleotides to the 3' end of a growing DNA strand, never to the 5' end. One possible reason for this is the fact that most DNA polymerases have a proofreading function that would not be energetically possible if DNA synthesis occurred in the 3' to 5' direction.

Sketch the reaction that DNA polymerase would have to catalyze if DNA synthesis occurred in the 3' to 5' direction.

Textbook Question

Assume that the sequence of bases shown below is present on one nucleotide chain of a DNA duplex and that the chain has opened up at a replication fork. Synthesis of an RNA primer occurs on this template starting at the base that is underlined.

If the RNA primer consists of eight nucleotides, what is its base sequence?

3'.......GGCTACCTGGATTCA....5'

Textbook Question

In the intact RNA primer, which nucleotide has a free 3'-OH terminus?

3'.......GGCTACCTGGATTCA....5'

Textbook Question

Reiji and Tuneko Okazaki conducted a now classic experiment in 1968 in which they discovered a population of short fragments synthesized during DNA replication. They introduced a short pulse of ³H-thymidine into a culture of E. coli and extracted DNA from the cells at various intervals. In analyzing the DNA after centrifugation in denaturing gradients, they noticed that as the interval between the time of ³H-thymidine introduction and the time of centrifugation increased, the proportion of short strands decreased and more labeled DNA was found in larger strands. What would account for this observation?

views