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A Visit With Dr. Francis Crick

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adenine- a nitrogen-containing base found in DNA molecules. Pairs with thymine.

base pair- two bases, each containing the element nitrogen, held together by relatively weak chemical bonds. Two base pairs make up DNA molecules: adenine and thymine, and guanine and cytosine.

Chargaff's rules- named for biochemist Erwin Chargaff, these rules describe the relationship of the amounts of the four nitrogenous bases which are found in DNA molecules. Specifically, Chargaff's rules state that the amount of adenine equals the amount of thymine, and that the amount of guanine equals the amount of cytosine in any DNA molecule.

cytosine- a nitrogen-containing base found in DNA molecules. Pairs with guanine.

deoxyribonucleic acid- also known as "DNA." The molecule which contains the hereditary information of most living organisms. This information is encoded in the sequence of bases arrayed along the length of the DNA molecule. DNA is a double helix, coiled around a central axis. The DNA backbones are composed of alternating sugar and phosphate subunits, while the interior portion of the molecule is composed of pairs of nitrogenous bases. The helix has a radius of 1 nm, and completes one 360 degree turn every 3.4 nm. The base pairs are 0.34 nm apart from each other. The two strands which make up the DNA molecule are anti-parallel--that is they run in opposite directions from each other.

genetic code - the arrangement of nucleotides, arranged in triplets known as "codons," which determines the identity and sequence of the amino acids which are used during protein synthesis. The "code" used to translate genetic information contained in the DNA molecule into a gene product.

guanine - a nitrogen-containing base found in DNA molecules. Pairs with cytosine.

isomers - a pair of chemical compounds composed of the same atomic subunits, and with the same molecular weight, but with different chemical or physical properties, and a different arrangement of component atoms in space.

macromolecule - a very large molecule made up of smaller subunits. Biological macromolecules include polysaccharides, nucleic acids, and proteins.

molecular biology - the branch of biology concerned with the structure and development of biological systems in terms of the biochemistry of their molecular components. Molecular biology overlaps a wide variety of other disciplines in use of molecular techniques e.g. PCR, RFLP analysis, etc.

neurobiology - the branch of biology concerned with the structure and function of cells of the nervous system.

tautomer - a molecule which can convert relatively easily from one isomeric form to another.

thymine - a nitrogen-containing base found in DNA molecules. Pairs with adenine.

vitalism - the idea that life processes have a component entirely separate from the constraints of the laws of natural science.

X-ray crystallography - a technique which allows elucidation of the structure of macromolecules. In this technique, an X-ray beam is passed through a crystal of a particular substance. The atoms which make up the crystal cause the X-rays to be deflected. This deflection pattern is directly dependent on the structure of the molecule being analyzed, and can thus be used to help determine the molecular structure.

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