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Animation: DNA Replication: An Overview

by Pearson
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DNA Replication: An Overview In principle, copying DNA, a process called DNA replication, is very simple. The two complementary DNA strands separate, and because each nucleotide can only pair with its complement, adenine with thymine and cytosine with guanine, each strand can be used as a template to build a new complementary strand, producing two DNA molecules. Here is a simplified close up of replication, showing what happens along one of the template DNA strands. Using a supply of free nucleotides, DNA polymerase assembles a new DNA strand along the template strand, following the base-pairing rules: adenine pairs with thymine, and cytosine pairs with guanine. Now let’s look at the DNA replication process. Replication of a DNA molecule begins at a specific sequence called an origin of replication. The two strands separate, forming a small replication bubble. DNA replication starts and then proceeds in both directions until the original DNA molecule is completely replicated. Each of the two daughter molecules consists of one old strand, shown in purple, and one new strand, shown in green. The DNA of a eukaryotic chromosome has multiple origins of replication. The multiple replication bubbles allow this very long molecule to be copied quite quickly, resulting in two daughter DNA molecules. In the cell, DNA replication is a little more complicated, but the principle is the same. For clarity, we have untwisted the double helix. Remember that each DNA strand has a 3 prime and 5 prime end, and the strands run in opposite directions. DNA replication begins at specific sites called origins of replication. Proteins attach here and separate the DNA strands, forming replication bubbles, which grow in both directions. Enzymes called DNA polymerases move along the template DNA strands and catalyze the elongation of new strands. Because DNA polymerases can only assemble new DNA in the 5 prime to 3 prime direction, only half of the new DNA can be synthesized in one continuous piece. The other half is synthesized in short pieces. As the replication bubbles grow, one daughter strand is synthesized continuously, while the other daughter strand is synthesized in pieces. The pieces are joined together by the enzyme DNA ligase. Eventually, all the replication bubbles merge, yielding two identical daughter DNA molecules. Now, let’s review the synthesis of DNA by assembling a new DNA strand. We’ll use the top DNA strand as the template and choose from the free nucleotides below. Note that D stands for deoxyribose and R stands for ribose. We're only using the deoxyribose nucleotides because we're building DNA, deoxyribonucleic acid.
DNA Replication: An Overview In principle, copying DNA, a process called DNA replication, is very simple. The two complementary DNA strands separate, and because each nucleotide can only pair with its complement, adenine with thymine and cytosine with guanine, each strand can be used as a template to build a new complementary strand, producing two DNA molecules. Here is a simplified close up of replication, showing what happens along one of the template DNA strands. Using a supply of free nucleotides, DNA polymerase assembles a new DNA strand along the template strand, following the base-pairing rules: adenine pairs with thymine, and cytosine pairs with guanine. Now let’s look at the DNA replication process. Replication of a DNA molecule begins at a specific sequence called an origin of replication. The two strands separate, forming a small replication bubble. DNA replication starts and then proceeds in both directions until the original DNA molecule is completely replicated. Each of the two daughter molecules consists of one old strand, shown in purple, and one new strand, shown in green. The DNA of a eukaryotic chromosome has multiple origins of replication. The multiple replication bubbles allow this very long molecule to be copied quite quickly, resulting in two daughter DNA molecules. In the cell, DNA replication is a little more complicated, but the principle is the same. For clarity, we have untwisted the double helix. Remember that each DNA strand has a 3 prime and 5 prime end, and the strands run in opposite directions. DNA replication begins at specific sites called origins of replication. Proteins attach here and separate the DNA strands, forming replication bubbles, which grow in both directions. Enzymes called DNA polymerases move along the template DNA strands and catalyze the elongation of new strands. Because DNA polymerases can only assemble new DNA in the 5 prime to 3 prime direction, only half of the new DNA can be synthesized in one continuous piece. The other half is synthesized in short pieces. As the replication bubbles grow, one daughter strand is synthesized continuously, while the other daughter strand is synthesized in pieces. The pieces are joined together by the enzyme DNA ligase. Eventually, all the replication bubbles merge, yielding two identical daughter DNA molecules. Now, let’s review the synthesis of DNA by assembling a new DNA strand. We’ll use the top DNA strand as the template and choose from the free nucleotides below. Note that D stands for deoxyribose and R stands for ribose. We're only using the deoxyribose nucleotides because we're building DNA, deoxyribonucleic acid.