Textbook Question
Which characteristics of DNA polymerase I raised doubts that its in vivo function is the synthesis of DNA leading to complete replication?
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8. DNA Replication
Overview of DNA Replication
1:51 minutesProblem 12
Textbook Question
Explain how RNA participates in DNA replication.
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RNA plays a role in DNA replication by providing a starting point for DNA synthesis. This is achieved through the synthesis of short RNA primers by the enzyme primase.
Primase synthesizes RNA primers complementary to the DNA template strand. These primers are typically 10-12 nucleotides long and are necessary because DNA polymerase cannot initiate synthesis on its own; it requires a free 3' hydroxyl group to add nucleotides.
Once the RNA primer is in place, DNA polymerase begins synthesizing the new DNA strand by adding deoxyribonucleotides to the 3' end of the primer, extending the strand in the 5' to 3' direction.
As replication progresses, the RNA primers are eventually removed by enzymes such as RNase H or DNA polymerase I, which degrade the RNA and replace it with DNA nucleotides.
Finally, DNA ligase seals the gaps between the newly synthesized DNA fragments (Okazaki fragments on the lagging strand), ensuring the continuity of the DNA molecule.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Role of RNA in DNA Replication
During DNA replication, RNA plays a crucial role as a primer. Primase, an enzyme, synthesizes short RNA primers that provide a starting point for DNA polymerase to begin adding DNA nucleotides. This is essential because DNA polymerase cannot initiate synthesis on its own; it can only extend an existing strand.
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Steps to DNA Replication
Types of RNA Involved
The primary type of RNA involved in DNA replication is messenger RNA (mRNA) and transfer RNA (tRNA), but in the context of replication, the focus is on the RNA primers synthesized by primase. These primers are complementary to the DNA template and are critical for ensuring accurate and efficient replication of the DNA strands.
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DNA Polymerase Function
DNA polymerase is the enzyme responsible for synthesizing new DNA strands by adding nucleotides to the growing chain. It requires the RNA primer to provide a free 3' hydroxyl group for nucleotide addition. Understanding the interaction between RNA primers and DNA polymerase is essential for grasping the mechanics of DNA replication.
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