Copying of DNA
CLASS NOTES from Science Prof Online
The process of copying the double-stranded DNA molecule is called replication.
Prokaryotes replicate their DNA (the nucleoid) throughout the interval between cell divisions. In eukaryotes, the timing of replication in the nucleus is highly regulated.
Article Summary: A cell must copy its DNA before it divides, so that both daughter cells have a complete copy of the genetic information. This article explains replication.
Genetic Replication – Copying of DNA
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Each double stranded
Replication begins at an origin (or many origins) along a DNA molecule, where the DNA is “unzipped” when paired nitrogenous bases are separated from each other. The openings in the DNA are called replication “bubbles.” At either end of these bubbles is a replication fork, a ‘Y’-shaped region of the bubble where new the strands of DNA are built. The enzyme helicase untwists the DNA at the replication fork, and another enzyme, DNA polymerase, catalyzes the construction of new DNA strands.
Prokaryotic DNA is arranged in a circular shape, with only one replication origin. Eukaryotes, which are more complex and have more DNA, form several replication bubbles, allowing the process of replication to be completed more quickly. Despite these differences, the underlying process of replication is the same for both prokaryotic and eukaryotic DNA.
The nucleotide building blocks of DNA are triphosphates (nucleotides with three phosphates) and energy is stored in the bonds that link the phosphates together. When one of these phosphate bonds break, this provides the energy to add that nucleotide to the growing nucleic acid molecule.
To learn more about molecular genetics see the following animations and SPO Class Note Articles:
- animation and review questions.
- animated video by FreeScienceLectures.com.
- step-through animation by John Kyrk.
- DNA Replication animated videos ( or ) from Howard Hughes Med Institute
- , Genetic Science Learning Center, University of Utah
- Deoxyribonucleic Acid Structure:
In the double-stranded DNA molecule, one strand runs from the 5’ end to the 3’ end, while the other runs 3’ to 5’. DNA polymerase, the enzyme that builds DNA strands, can only add nucleotides at the free 3’ end of a growing strand, always forming the new DNA strands in the 5’ to 3’ direction only.
How Do Nucleotides Put Themselves Together Into New Nucleic Acid Strands?
The construction of a nucleic acid is an anabolic polymerization process. Anabolic reactions use energy to build bigger molecules. Polymerization is the process of taking monomers, such as nucleotides, and putting them together into polymers (large molecules composed of many monomers).
Leading and Lagging Strand
Each of DNA’s two sugar phosphate backbones run in opposite directions, so they are considered anti-parallel. The end of each strand is distinct, with the 5’ (five prime) end terminating in a phosphate, and the 3’ (three prime) end with a dangling hydroxyl group (OH-).
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Portions of this article originally appeared on Suite101 online magazine.
Page last updated: 5/2013
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