RNA Primer in DNA Replication: Definition, Function & Sequence

RNA Primer in DNA Replication: Definition, Function & Sequence
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  • 0:00 Complementary Nucleotides
  • 1:43 Overview of DNA Replication
  • 2:46 The Role of RNA Primers
  • 4:15 Lesson Summary
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Lesson Transcript
Instructor: Jennifer Gilley
During DNA replication, an RNA primer serves as a starting point for DNA polymerase, which builds complementary DNA. This lesson will focus on the sequence, function, and definition of the RNA primer during this process.

Complementary Nucleotides

Our cells use both DNA and RNA to make the various proteins required for daily cellular activities. DNA and RNA are made up of different sequences of nucleotides, or genetic building blocks. Adenine (A), cytosine (C), and guanine (G) are nucleotides found within both DNA and RNA. However, only DNA contains thymine (T), and only RNA contains uracil (U).

Each nucleotide within DNA and RNA has a complementary nucleotide that it can pair with. This is somewhat similar to the idea of complementary colors that work well together: blue always complements orange, just as green works well with red. In DNA, adenine is complementary to thymine, and guanine is complementary to cytosine. In RNA, adenine is complementary to uracil, and guanine remains complementary to cytosine.

Keep in mind that there is no uracil in DNA and no thymine in RNA. However, DNA and RNA can still be complementary to one another even though they may have different nucleotides. For instance, uracil within RNA will still be complementary to an adenine in DNA just as an adenine in RNA will be complementary to a thymine in DNA. In other words, adenine will pair with either thymine in DNA or uracil in RNA, and guanine will always pair with cytosine in both DNA and RNA. Therefore, each nucleotide has a partner that it always associates with depending on if it's in a molecule of DNA or RNA. The following figure demonstrates the complementary nature of both DNA and RNA nucleotides.

Overview of DNA Replication

Now that we understand how complementarity works in DNA and RNA, we can begin to understand how our cells make copies of DNA when necessary. Our cells age and constantly need to be replaced by new cells. For this to happen, the cell must first make a copy of the DNA before a new one is produced through cell division. This ensures that the new cell will have the full set of DNA found in every other cell. DNA replication is the term for the process that copies our DNA before a new cell is made. During this process, the DNA must first be unwound or unzipped from its complementary strand. Then each strand is used as a template to build a new complementary piece of DNA. In the figure seen here, the red strands of DNA represent the original pieces of DNA, and the pink strands signify the new complementary pieces of DNA that are built during replication.

At the end of replication, each set of DNA consists of one original strand and one new strand.

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