DNA
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Deoxyribonucleic acid is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning,
Simplified diagram
Impure DNA extracted from an orange
A current model of meiotic recombination, initiated by a double-strand break or gap, followed by pairing with an homologous chromosome and strand invasion to initiate the recombinational repair process. Repair of the gap can lead to crossover (CO) or non-crossover (NCO) of the flanking regions. CO recombination is thought to occur by the Double Holliday Junction (DHJ) model, illustrated on the right, above. NCO recombinants are thought to occur primarily by the Synthesis Dependent Strand Annealing (SDSA) model, illustrated on the left, above. Most recombination events appear to be the SDSA type.
Maclyn McCarty (left) shakes hands with Francis Crick and James Watson, co-originators of the double-helix model based on the X-ray diffraction data and insights of Rosalind Franklin and Raymond Gosling.
Polymer
Videos
A polymer is a substance composed of macromolecules. A macromolecule is a molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derive
DNA
…Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development…
Appearance of real linear polymer chains as recorded using an atomic force microscope on a surface, under liquid medium. Chain contour length for this polymer is ~204 nm; thickness is ~0.4 nm.
A polyethylene sample that has necked under tension
A plastic item with thirty years of exposure to heat and cold, brake fluid, and sunlight. Notice the discoloration and crazing of the material (compared with replacement item in foreground).
Chlorine attack of acetal resin plumbing joint