Dna 4 Essay, Research Paper
The molecule responsible for the transformation of characteristics form one generation to the next is called DNA. The genetic material, located in the chromosomes is a combination of acid and histones. DNA is made up of units called nucleotides. Nucleotides are made up of 3 components, a five carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base. This base can be either adenine, guanine, thymine or cytosine.
There are 2 strands of nucleotides in a double-helix – they are anti-parallel, meaning they go in opposite directions. Double stranded DNA is located in the chromosome. DNA and proteins together make up chromatin which is foiled and coiled.
DNA makes an exact copy of itself just before cell division begins. This process of DNA duplication is known as replication. The hydrogen bond between the base pairs of the 2 nucleotide strands weaken, and the 2 strands break apart. Each strand acts as a template forming a new nucleotide. This is accomplished by the acting of 2 sets of enzymes – DNA helicase enzymes and DNA polymerase enzymes. The DNA helicase enzymes separate the 2 nucleotide strands. The site where the helicase is working and where replication is taking place is known as the DNA fork. The polymerase enzyme helps the nitrogenous base in a given nucleotide to pick up and attach to a complementary base at the 3′ end of the DNA template. The 5′-3′ strand of template is duplicated in short segments called Okazaki fragments. Ligase is the enzyme that joins the fragments together. The end product of this is an exact copy of the original DNA.
DNA must also be stable, but able to be changed. We know that DNA is stable because of the tightly wound, double helix ladder formation. Also the bonds that keep everything together are hydrogen bonds, one of the stronger bonds. We also know that DNA can be changed because during the replication process, DNA crosses over and reverses the order of the material. The base pairs can be altered during the crossing over process. This altering is what causes different characteristics in offspring.
DNA is complex enough to determine an organisms phenotype. Phenotype is determined by the combination and location of the different base pairs. These base pairs mix and match during the crossing over phase. Different combinations of base pairs create different features and characteristics. These combinations are responsible for making me look different from you.
The idea that DNA copies itself was proved in the famous 1952 Hershey-Chase experiment. In this experiment they prepared 2 samples of viruses, one in which the DNA was radioactive isotope of phosphorous, and the other in which the protein was labeled with radioactive isotope of sulphur. After some time it was visible that radioactive phosphorous was present in the virus, and not the radioactive sulphur. The 2 scientists then concluded that DNA was responsible for the transmission of characteristics, and that protein had nothing to do with it. If DNA did not have the ability to copy itself, Hershey and Chase would have never been able to prove the DNA is in fact responsible for the transmission of traits.
In conclusion, DNA – God’s secret recipe for making you, has the ability to copy itself, is stable, yet able to be changed, and is also complex enough to determine a persons phenotype. DNA carries traits from parents to child, and then to the child’s children. As long as there are humans in the world, a person can never truly die because they traits will always be present in their offspring.
1. Cliff’s quick review – Biology
2.Cliff’s AP Biology preparation guide
3.Fifth Edition Biology