The Structure of the DNA Molecule

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Adenine: A nitrogenous base. Pairs with thymine in DNA molecules.

Bacteriophage: A virus whose host is a bacterium. Also called phage.

Base: See nitrogenous base.

Base Pair: Two nitrogenous bases held together by weak bonds. in a DNA molecule adenine always pairs with thymine while cytosine always pairs with guanine. Thus, one DNA strand directs the synthesis of the other strand. This specificity of DNA base pairing is what enables accurate replication of a DNA molecule.

Chromosome: a self-replicating genetic structure, composed primarily of proteins and DNA, which carry nucleotide sequences known as genes.

Complementary base pair: a pair of bases in which the identity of one base defines the identity of its partner base. E.g.: In a DNA molecule there are two complementary base pairs--Adenine and thymine, and guanine and cytosine.

Cytosine: A nitrogenous base. Pairs with guanine in DNA molecules.

DNA (deoxyribonucleic acid): the molecule that encodes genetic information. DNA is composed of two anti-parallel strands which wind about a common axis to form a double helix. Each strand of DNA is composed of a linear array of nucleotides bonded in such a way that the bases extend toward the central axis of the molecule while the two backbones are composed of alternating sugar and phosphate subunits. The bases of the two strands are weakly bonded to each other in a complementary fashion. in other words, an adenine is always bound to a thymine while a cytosine is always bound to a guanine.

Gene: An ordered sequence of nucleotides which act as the functional subunit of hereditary information. The collection of genes in an organism determine the characteristics of that organism.

Guanine: A nitrogenous base. Pairs with cytosine in DNA molecules.

Meiosis: the process of cell division in which a single cell produces four daughter cells each of which contains half of the number of chromosomes of the parent cell. For example, a single diploid spermatogonium (primordial germ cell) will divide meiotically to produce 4 haploid sperm cells.

Mitosis: the process of cell division in which a single cell produces two daughter cells which are identical to on another, and to the original parent cell.

Nitrogenous base: a molecule with the properties of a base, which also contains the element nitrogen.

Nucleic acid: a large molecule composed of repeating nucleotides

Nucleotide: A subunit of DNA or RNA composed of a nitrogenous base, a phosphate molecule, and a pentose sugar molecule.

Pentose sugar: A sugar molecule containing five carbon atoms. E.g.: deoxyribose.

Phage: A virus which infects a bacterial cell. Also called a Bacteriophage.

Purine: A nitrogen- containing, single ring compound that occurs in nucleic acids. In DNA molecules, the purines are adenine and guanine.

Pyrimidine: A nitrogen containing, double ring compound that occurs in nucleic acids. In DNA molecules, the pyrimidines are cytosine and thymine.

Radioactive phosphorus (32P): radioactive isotope of 31P, an element found in DNA molecules.

Radioactive sulfur (35S): radioactive isotope of 32S, an element found in proteins

T Phages: A phage which infects Escherichia coli. Viral parasites of this type are labeled T1 through T7. T2 was the first phage observed under the electron microscope.

Thymine: A nitrogenous base. Pairs with adenine in DNA molecules.

Virus: A particle consisting of a nucleic acid core surrounded by a protein coat. New virus particles can only be produced by a cell which is infected by the virus.

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