DNA Replication WebsitesDNA Replication Overview
This website gives a great overview of the DNA replication process. DNA makes DNA Awesome website about DNA replication. A really cool graphic that give information for each and every step. DNA Replication |
DNA Replication Youtubes |
Enzymes Involved in DNA Replication
1. Helicase- splits the DNA strand apart.
2. DNA Polymerase- Binds a leading strand of DNA nucleotides starting at the 3' end of RNA primer working to the 5' end.
3. RNA Primase- lays down more RNA primer in the gaps, this makes the Okazaki Fragment.
4. Exonuclease- takes off the RNA primer so that DNA polymerase can replace it with DNA nucleotides.
5. Ligase- inserts phosphate into any gaps in the sugar-phosphate backbone of the DNA strand.
2. DNA Polymerase- Binds a leading strand of DNA nucleotides starting at the 3' end of RNA primer working to the 5' end.
3. RNA Primase- lays down more RNA primer in the gaps, this makes the Okazaki Fragment.
4. Exonuclease- takes off the RNA primer so that DNA polymerase can replace it with DNA nucleotides.
5. Ligase- inserts phosphate into any gaps in the sugar-phosphate backbone of the DNA strand.
DNA Relication
Image from: http://www.contexo.info/DNA_Basics/DNA%20Replication.htm
DNA Replication
DNA replication starts at a place called the origins of replication. These are short areas of DNA that have the sequence of nucleotides that code for the DNA to start replicating. The DNA recognizes the starter sequence and helicase attaches itself to the DNA and starts separating the two strands making a replication “bubble”. Replication occurs in both directions and continues to copy until both strands are copied identically. At the end of each replication bubble, there is a y-shaped region called the replication fork. This is where the parent strands, or the original strands of the DNA, are started to be separated by an enzyme called helicase. By the two strands separating this makes them available to be copied. After some is separated, single-strand binding proteins are bound to the unpaired DNA strands to stabilize them. These parent strands are going to be the templates for the new DNA. The initial strand put on top of the DNA parent chain is not actually DNA, it is a RNA primer. This primer is laid down, synthesized by another enzyme called primase. The RNA polymerase lays down an RNA chain of single nucleotides using the parent chain as a template. RNA polymerase is like DNA polymerase, it adds to the 3’ end but elongates the cell 5’ to 3’. Because of this layer of RNA polymerase, the DNA is now ready to get DNA laid on it and is elongated in the 3’ direction. It is read from 3’ to the 5’ end.
The enzyme DNA polymerase catalyzes the synthesis of DNA by adding nucleotides to the parent DNA strand. DNA polymerase requires the primer and a DNA template strand to replicate.
DNA Replication of the Antiparallel Strand
In DNA, the structure of the two stands are opposite, one strand runs from 5’ to 3’ and the other runs from 3’ to 5’. But when DNA is being replicated the new stuff is always added to the 3’ end. While the two strands are being replicated at the same time during replication gets complicated. This means that the two strands must also be replicated antiparallel as well. For the replication process this means that the new DNA strand must elongate 5’ to 3’. DNA polymerase has the ability to make a “complementary strand” that elongates the new DNA. DNA polymerase rests in the replication fork on the parent strand and adds nucleotides to the new strand and the fork moves. This strand that is being made this way is called the leading strand. This DNA polymerase used in this process only needs one primer.
When working with the other strand, it is necessary to work in the 5’ to 3’ direction. This means that DNA polymerase must work away from the replication fork. This DNA strand that is elongating is called the lagging strand. The lagging strand is made irregularly unlike the leading strand. The segments in the lagging strand are called Okazaki fragments. For these fragments they must be primed separately. Another DNA polymerase comes in and takes the spot of the RNA nucleotide by using the enzyme called Exonuclease. When DNA is added it is added one by one to the 3’ end that is next to the Okazaki fragment. But at this point DNA polymerase cannot join to the first nucleotide of the Okazaki fragment. So DNA ligase comes in and joins the two with a sugar-phosphate backbone.Information from: Campbell, Neil A., and Jane B. Reece. Biology. New York: Custom Publishing, 2008. Print.
DNA replication starts at a place called the origins of replication. These are short areas of DNA that have the sequence of nucleotides that code for the DNA to start replicating. The DNA recognizes the starter sequence and helicase attaches itself to the DNA and starts separating the two strands making a replication “bubble”. Replication occurs in both directions and continues to copy until both strands are copied identically. At the end of each replication bubble, there is a y-shaped region called the replication fork. This is where the parent strands, or the original strands of the DNA, are started to be separated by an enzyme called helicase. By the two strands separating this makes them available to be copied. After some is separated, single-strand binding proteins are bound to the unpaired DNA strands to stabilize them. These parent strands are going to be the templates for the new DNA. The initial strand put on top of the DNA parent chain is not actually DNA, it is a RNA primer. This primer is laid down, synthesized by another enzyme called primase. The RNA polymerase lays down an RNA chain of single nucleotides using the parent chain as a template. RNA polymerase is like DNA polymerase, it adds to the 3’ end but elongates the cell 5’ to 3’. Because of this layer of RNA polymerase, the DNA is now ready to get DNA laid on it and is elongated in the 3’ direction. It is read from 3’ to the 5’ end.
The enzyme DNA polymerase catalyzes the synthesis of DNA by adding nucleotides to the parent DNA strand. DNA polymerase requires the primer and a DNA template strand to replicate.
DNA Replication of the Antiparallel Strand
In DNA, the structure of the two stands are opposite, one strand runs from 5’ to 3’ and the other runs from 3’ to 5’. But when DNA is being replicated the new stuff is always added to the 3’ end. While the two strands are being replicated at the same time during replication gets complicated. This means that the two strands must also be replicated antiparallel as well. For the replication process this means that the new DNA strand must elongate 5’ to 3’. DNA polymerase has the ability to make a “complementary strand” that elongates the new DNA. DNA polymerase rests in the replication fork on the parent strand and adds nucleotides to the new strand and the fork moves. This strand that is being made this way is called the leading strand. This DNA polymerase used in this process only needs one primer.
When working with the other strand, it is necessary to work in the 5’ to 3’ direction. This means that DNA polymerase must work away from the replication fork. This DNA strand that is elongating is called the lagging strand. The lagging strand is made irregularly unlike the leading strand. The segments in the lagging strand are called Okazaki fragments. For these fragments they must be primed separately. Another DNA polymerase comes in and takes the spot of the RNA nucleotide by using the enzyme called Exonuclease. When DNA is added it is added one by one to the 3’ end that is next to the Okazaki fragment. But at this point DNA polymerase cannot join to the first nucleotide of the Okazaki fragment. So DNA ligase comes in and joins the two with a sugar-phosphate backbone.Information from: Campbell, Neil A., and Jane B. Reece. Biology. New York: Custom Publishing, 2008. Print.
Okazaki Fragments
Okazaki fragments are "a short segment of DNA synthesized away from the replication fork on a template strand during DNA replication, many of which are joined together to make up the lagging strand of the newly synthesized DNA." Information from: Campbell, Neil A., and Jane B. Reece. Biology. New York: Custom Publishing, 2008. Print.