Introduction Into DNA Studies

1. Describe the structure of DNA.

DNA molecules are composed of two strands that form a helical ascending spiral. They fit together like the opposing teeth of a zipper and are held together by weak interactions called hydrogen bonds. These two strands is a long string of subunits called nucleotides, each attached to the one immediately about it and the one immediately below it to form a long chain. Each nucleotide contains a five-carbon sugar.

The five-carbon sugar contains a five-membered ring with an oxygen atom as one of the vertices. Each nucleotide also features a phosphate group and a nitrogen-containing base; these bases are typically represented by adenine, cytosine, thymine, and guanine. The base is attached to carbon 1 of the sugar, biologist denote each of the carbons in the sugar using a number from 1 through 5, where 1 represents the carbon to which the base is attached.

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2. How does an organism’s genotype determine its phenotype?

The genotype of an organism is the sum total of all the genes that it inherits. It is sort of like a blueprint that is designed to serve as a guide in the development of the organism, so that it will become the same kind of creature as the parent or parents that it came from. The phenotype, the organism’s physical trait arises from the actions of a wide variety of proteins. For example structural proteins help make up the body of an organism, and enzymes catalyze its metabolic activity. A gene does not build a protein directly, but rather dispatched instructions in the form of RNA, which in turn programs protein synthesis. The molecular chain of command is from DNA in the nucleus to RNA to protein in the cytoplasm.

3. Describe each stage of the flow of information starting with DNA and ending with a trait.

DNA and RNA are long linear polymers, called nucleic acids that carry information in a form that can be passed from one generation to the next. These macromolecules consist of one large number of linked nucleotides, each composed of a sugar, a phosphate, and a base. Sugar is linked by phosphates from a common backbone, whereas the bases vary among four kinds.

Genetic information is stored in the sequence of bases along a nucleic acid chain. The bases from a specific pair with one another that are stabilized by hydrogen bonds. The base pairing results in the formation of a double helix. A helix structure consisting of two strands. Genetic information in DNA is transcribed into RNA and then translated into polypeptides. These processes occur through transcription and translation when a segment of DNA is transcribed, the results is an RNA molecule.

Transcription is taken placed because the nucleic acid language of DNA has simply been rewritten as a sequence of bases of RNA; the language is still that of nucleic acids. The nucleotide bases of the RNA molecules are complementary to those on the DNA strand. Translation is the conversion of the nucleic acids' language to the polypeptide language. Like nucleic acids polypeptides are polymers, but the monomers that make them up are the 20 amino acids common to all organisms. The genetic instructions for the amino acid sequence of a polypeptide chain are written in DNA and RNA as a series of three-base word codons. Codons are the DNA is transcribed in the RNA, and then the RNA codons are translated into amino acids that form polypeptides. Codons in mRNA are read sequentially by tRNA molecules, which serve as adaptors in protein synthesis.

References:

1. Berg J. M, Tymoczko, J. L, Stryer, L Bio Chemistry. 5th edition. New York: W. H Freeman; 2002 Chapter 5, DNA, RNA, and the Flow of Genetic Information retrieved from http://www. ncbi. nlm. gov/books/NBK21171 2012
2. Miller, C. Forms of Genotypes retrieved from http://www. ehow. com/info_8678611_forms-genetics

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