РефератыИностранный языкHeHeredity Essay Research Paper Deoxyribonucleic acid and

Heredity Essay Research Paper Deoxyribonucleic acid and

Heredity Essay, Research Paper


Deoxyribonucleic acid and ribonucleic acid are two chemical substances


involved


in transmitting genetic information from parent to offspring. It was


known early into the


20th century that chromosomes, the genetic material of cells, contained


DNA. In 1944,


Oswald T. Avery, Colin M. MacLeod, and Maclyn McCarty concluded that DNA


was the


basic genetic component of chromosomes. Later, RNA would be proven to


regulate


protein synthesis. (Miller, 139)


DNA is the genetic material found in most viruses and in all


cellular organisms.


Some viruses do not have DNA, but contain RNA instead. Depending on the


organism,


most DNA is found within a single chromosome like bacteria, or in several


chromosomes


like most other living things. (Heath, 110) DNA can also be found


outside of


chromosomes. It can be found in cell organelles such as plasmids in


bacteria, also in


chloroplasts in plants, and mitochondria in plants and animals.


All DNA molecules contain a set of linked units called


nucleotides. Each


nucleotide is composed of three things. The first is a sugar called


deoxyribose. Attached


to one end of the sugar is a phosphate group, and at the other is one of


several


nitrogenous bases. DNA contains four nitrogenous bases. The first two,


adenine and


guanine, are double-ringed purine compounds. The others, cytosine and


thymine, are


single-ringed pyrimidine compounds. (Miller, 141) Four types of DNA


nucleotides can


be formed, depending on which nitrogenous base is involved.


The phosphate group of each nucleotide bonds with a carbon from


the


deoxyribose. This forms what is called a polynucleotide chain. James D.


Watson and


Francis Crick proved that most DNA consists of two polynucleotide chains


that are


twisted together into a coil, forming a double helix. Watson and Crick


also discovered


that in a double helix, the pairing between bases of the two chains is


highly specific.


Adenine is always linked to thymine by two hydrogen bonds, and guanine is


always linked


to cytosine by three hydrogen bonds. This is known as base pairing.


(Miller, 143)


The DNA of an organism provides two main functions. The first


function is to


provide for protein synthesis, allowing growth and development of the


organism. The


second function is to give all of it s descendants it s own


protein-synthesizing information


by replicating itself and providing each offspring with a copy. The


information within the


bases of DNA is called the genetic code. This specifies the sequence of


amino acids in a


protein. (Grolier Encyclopedia, 1992) DNA does not act directly in the


process of


protein synthesis because it does not leave the nucleus, so a special


ribonucleic acid is used


as a messenger (mRNA). The mRNA carries the genetic information from the


DNA in the


nucleus out to the ribosomes in the cytoplasm during transcription.


(Miller, 76)


This leads to the topic of replication. When DNA replicates, the


two strands of


the double helix separate from one another. While the strands separate,


each nitrogenous


base on each strand attracts it s own complement, which a

s mentioned


earlier, attaches


with hydrogen bonds. As the bases are bonded an enzyme called DNA


polymerase


combines the phosphate of one nucleotide to the deoxyribose of the


opposite nucleotide.


This forms a new polynucleotide chain. The new DNA strand stays attached


to the old


one through the hydrogen bonds, and together they form a new DNA double


helix


molecule. (Heath, 119) (Miller, 144-145)


As mentioned before, DNA molecules are involved in a process


called protein


synthesis. Without RNA, this process could not be completed. RNA is the


genetic


material of some viruses. RNA molecules are like DNA. They have a long


chain of


macromolecules made up of nucleotides. Each RNA nucleotide is also made


up of three


basic parts. There is a sugar called ribose, and at one end of the sugar


is the phosphate


group, and at the other end is one of several nitrogenous bases. There


are four main


nitrogenous bases found in RNA. There are the double-ringed purine


compounds adenine


and guanine, and there is the single-ringed pyrimidine compounds of uracil


and cytosine.


(Miller, 146)


RNA replication is much like that of DNA s. In RNA synthesis, the


molecule


being copied is one of the two strands of a DNA molecule. So, the


molecule being


created is different from the molecule being copied. This is known as


transcription.


Transcription can be described as a process where information is


transferred from DNA to


RNA. All of this must happen so that messenger RNA can be created, the


actual DNA


cannot leave the nucleus. (Grolier Encyclopedia, 1992)


For transcription to take place, the RNA polymerase enzyme is


needed first


separate the two strands of the double helix, and then create an mRNA


strand, the


messenger. The newly formed mRNA will be a duplicate of one of the


original two


strands. This is assured through base pairing. (Miller, 147)


When information is given from DNA to RNA, it comes coded. The


origin of the


code is directly related to the way the four nitrogenous bases are


arranged in the DNA. It


is important that DNA and RNA control protein synthesis. Proteins control


both the cell s


movement and it s structure. Proteins also direct production of lipids,


carbohydrates, and


nucleotides. DNA and RNA do not actually produce these proteins, but tell


the cell what


to make. (Heath, 111-113)


For a cell to build a protein according to the DNA s request, a


mRNA must first


reach a ribosome. After this has occurred, translation can begin to take


place. Chains of


amino acids are constructed according to the information which has been


carried by the


mRNA. The ribosomes are able to translate the mRNA s information into a


specific


protein. (Heath, 116) This process is also dependent on another type of


RNA called


transfer RNA (tRNA). Cytoplasm contains all amino acids needed for


protein


construction. The tRNA must bring the correct amino acids to the mRNA so


they can be


aligned in the right order by the ribosomes. (Heath, 116) For protein


synthesis to begin,


the two parts of a ribosome must secure itself to a mRNA molecule.


(Miller, 151)

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