DNA Replication

DNA can replicate to make identical copies of the DNA strands. DNA replication starts with the double helix during the initiation stage when Helicase (an enzyme) is used to "unzip" the DNA. In other words Helicase seperates the two double stranded DNA to seperate strands of DNA, one being the lagging strand and the other the leading strand.

The next step in DNA replication is Elongation , this starts at the replication fork. RNA primase starts this process by adding RNA primers to the DNA strands. the primers are like a green light for the replication to start. DNA replication cannot start though, until RNA primase has added a primer. DNA polymerase starts to add DNA nucleotides from the 3' to 5' ends of the DNA. Since the nucleotides can only be added from the 3' to 5' end, the lagging strand is discontinual. polyermase will add a fragment of DNA nucleotides known as Okazaki fragments (shown in picture above). Polymerase will make a bunch of these Okazaki fragments on the lagging strand. The leading strand on the other hand is a continous replication. The leading strand is already in the 3' to 5', so DNA polymerase can start from the primers and continue without stoping or making Okazaki fragments.

The last step of DNA replication is Termination. Termination occurs when DNA polymerase reaches the end of the strands. the RNA primers are removed and ligase comes and connects the Okazaki fragments together on the lagging strand. This completes the replication of DNA.

DNA Structure

Adenine and Guanine are purines. Cytosine and Thymine are pyrimidines. Purines are larger. A purine and a pyrimidine must pair together, so that the DNA is a certian width. If two pyrimidines were paired together, the DNA would be too narrow, if two purines were paired together the DNA would be too wide. This is way Adenine pairs with Thymine and Guanine pairs with Cytosine.

DNA is constructed by a phosphate backbone, which are held together by phosodiester bonds. DNA starts with a phosphate attached to a deoxyribose sugar, which is attached to one for the four base pairs. DNA is double stranded, which forms a twist of the strands, which is called a double helix.

Rosalind Franklin took the first x-ray of DNA, this x-ray is known as photo 51. From this photo Watson and Crick were able to make the first model of DNA as a double helix. From the photo they were also able to tell how far apart the nucleotides are from eachother. They figured out that DNA makes one complete twist every 10 nucleotides. There are also .34 nm between each base pair and 3.4 nm is one full twist. DNA is also antiparell, which runs 3' to 5'. Watson and Crick later received a noble prize for their work with DNA structure. Rosalind Franklind died before she was recognized and never received a noble prize.

What is DNA?

DNA is short for Deoxyribonucleic acid. Every person has DNA inside of almost all of the cells in their body. It is the building block for each persons genetic makeup. No two people have the same DNA, and is inherited from parent to offspring (will be covered later). Most DNA is located in the the cell nucleus and some is located in the mitochondria. DNA is made up of four base pairs, A (Adenine), G (Guanine), T (Thymine) and C (Cytosine). In DNA Adenine always pairs with Thymine and Cytosine always pairs with Guanine. DNA has a specific structure and can be replicated ( will be discussed later). DNA is often compared to a blueprint that construction workers use before the actual construction of a building, because it contains the information needed for the entire body.