DNA Sequencing
DNA sequencing refers to the process by which the base order of a nucleotide sequence is elucidated § The most widely used method for DNA sequencing involves the use of chain-terminating…
Okazaki Fragments
DNA polymerase cannot initiate replication, it can only add new nucleotides to an existing strand For DNA replication to occur, an RNA primer must first be synthesised to provide an attachment point…
How DNA Works
DNA Replication The double helix of DNA unwinds and each side serves as a pattern to make a new molecule. DNA carries the information for making all of the cell's…
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…
