Structure and Function of Cellular Genomes
Genotype versus Phenotype All cellular activities are encoded within a cell’s DNA. The sequence of bases within a DNA molecule represents the genetic information of the cell. Segments of DNA…
The Central Dogma
The central dogma of molecular biology describes the two-step process, transcription and translation, by which the information in genes flows into proteins: DNA → RNA → protein. Transcription is the…
Packaging of DNA Helix in Prokaryotes and Eukaryotes
Packaging in Prokaryotes: In prokaryotes like E. coli, a well-defined nucleus is absent. So, DNA (carrying negative charge) is held together with some proteins (that have positive charge) in a…
Hoogsteen and reverse Hoogsteen base pairs
The A·U (or A·T) Hoogsteen pair is a well-known type of base pair (bp), named after the scientist who discovered it. As shown in the Figure below (left), in the…
Franklin’s X-Ray Crystallography Experiments
Refractions & Reflections on the Nature of Science Regular substances like crystals diffract X-rays in characteristic patterns according to their physical structure. The X-ray crystallograph at right ("Photo 51") shows an exceptionally clear…
The Watson-Crick Model of DNA (1953)
Deoxyribonucleic Acid (DNA) is a double-stranded, helical molecule. It consists of two sugar-phosphate backbones on the outside, held together by hydrogen bonds between pairs of nitrogenous bases on the inside. The bases are of four types (A, C, G,…
Chargaff’s Rule of Base Pairing
The rules of base pairing (or nucleotide pairing) are: This is consistent with there not being enough space (20 Å) for two purines to fit within the helix and too…
History of DNA Models
Up until James Watson and Francis Crick's experiments, we had very little understanding of exactly what made living things look and appear as they do. Other models had been proposed,…
DNA Strand Diagram
The below mentioned article provides a diagram of DNA strand. (a) DNA is made up of two polynucleotide chains. The backbone is constituted by sugar-phosphate, while the nitrogenous bases project…
Secondary Structure of DNA and RNA
Secondary Structure of Deoxyribonucleic Acids: Some observations made on deoxyribonucleic acids in solution suggested that DNA molecules — as they could be extracted from cells — had structural characteristics different…
