Реферат: DNA Essay Research Paper Nucleotides are important
DNA Essay, Research Paper
Nucleotides are important to the structure of DNA. In this essay, I defined the term and explained what the function of a nucleotide is through explanation and illustration.
A nucleotide, as defined in my computer?s Microsoft Bookshelf, is a subset of the DNA ladder shown in question number one. They are the building blocks of nucleic acids, and are half of one of the ladder?s ?rungs? and its support beams. Nucleotides make up the double helix, and the sequence of them determines the cell?s genetic code. Thus, nucleotides are very important to a cell?s structure and division.
The G.B.E. textbook glossary states that a nucleotide is ?a nucleoside attached to a phosphate group,? and a nucleoside is a base attached to a sugar. Therefore, nucleotides contain three basic elements: one pentose sugar, one phosphate group, and one of four nitrogenous base.
The pentose, or 5-carbon (atom) sugar in DNA is called deoxyribose, which possesses one less oxygen atom than RNA?s sugar, ribose. A more detailed deoxyribose sugar molecule is shown below (this molecule is really 3-d).
The phosphate group is made up of one phosphate atom surrounded by four oxygen atoms,
two having a single bond and the other two having a double bond. The diagram below shows the
setup of one phosphate group.
There are four nitrogenous bases found in nucleic acids: adenine (A), guanine (G), cytosine (C), and thymine (T). Adenine and guanine are classified as purines due to their double-ring structures, and the two single-ring structures, known as pyrimidines, are cytosine and thymine. The replacement for thymine, uracil, is also a nitrogenous base, but only in RNA, which will be discussed in detail later.
1.We know now that DNA is a nucleic acid which carries genetic information in the cells of organisms, but confusion existed since more than a century ago as to exactly what that genetic information was.
In 1868, Friedreich Miescher was the first to separate a cellular organelle from the cell. This organelle was the nucleus, and it was studied to determine the origin of a cell?s genetic information. The nucleus was thought to be a carrier of this material because it was known that genes are found on chromosomes, so Miescher successfully separated it and studied a substance he named ?nuclein.?
Miescher?s nuclein was later found to contain deoxyribonucleic acid, or DNA, and ribonucleic acid, or RNA, which was direct evidence to explain the origin of the genetic material. However, scientists persisted to believe that (histone) protein, found also in the nucleus, was the source of the material.
Those scientists had good reason to believe that protein was the genetic material, which led to much confusion. The nucleus contains thousands of different, complex proteins, and only two kinds of nucleic acids, which were very simple. Also, 20 different amino acids made up protein molecules, where only four nucleotides made up DNA. Proteins in the nucleus were studied far more in depth than nucleic acids in the beginning of the twentieth century, which also led to the confusion of many scientists.
These strong reasons were enough to sway scientists? beliefs from the truth, that DNA is the real genetic material. Everyone was in the dark until about 1950.
2.In this essay, I explained the two experiments which supported the hypothesis that stated that DNA is the genetic material in the cell.
The first experiments in 1944 involved scientists Oswald Avery, Colin MacLeod, and MacLyn McCarty, and they included the previous studies of Fredrick Griffith. In the 1920s, Griffith experimented on mice, in which he involved two strands of bacteria: IIIs (smooth strand) and IIR (rough strand).
The experiment included the process of transformation, which the textbook describes as a ?transfer of a genetic trait from one string of bacteria to another.? Griffith concluded that the genetic material in killed bacterial cells could genetically change in the IIR strain. The material was extracted from the IIIS strain, and was able to form a capsule for the IIIS strain, making it pathogenic.
The arrangement was then treated with protein-digesting enzymes called protease, as well as RNA, which did not affect the transformation process, but did isolate DNA in the cell. The arrangement was treated with a DNA-digesting enzyme, and transformation was terminated!
This experiment concluded that, in bacteria, ?DNA is the genetic material?, and that it ?controls the synthesis of specific products.?*
The second experiment to support the hypothesis that DNA is the genetic material was performed by Alfred Hershey and Martha Chase in 1951.
These two scientists used a virus called T2 bacteriophage to test this hypothesis. The bacteriophage consists of a protein coating and DNA inside, and the virus attacks a bacteria cell to transfer its DNA to the cell.
Hershey and Chase first treated the protein coat of the virus with a radioactive material, and the bacteriophage attacked the bacteria normally. The scientists then observed, after sort the protein from the genetic material, that the progeny contained no radioactivity. Hershey and Chase *Pg. 149
performed a similar experiment, this time treating the genetic material of the bacteriophage. Again, after attacking the bacteria cell, the progeny contained no radioactivity.
The final step of the experiment involved treating the bacteria with a new, hot, radioactive T2 bacteriophage. The scientists observed that the progeny viruses were found to be radioactive!
Therefore, since the progeny was radioactive, DNA must be the genetic material!
These two strong and important experiments helped the field of genetics by greatly supporting the hypothesis that DNA is, in fact, the genetic material of the cell.