Chromosome mutation II
Change in Number One of the major type o chromosome mutation is change in chromosome number. There are two types of numerical changes (1) Euploidy and (2)Aneuploidy 1. Euploidy: (eu = true, ploidy = set of chromosomes) The number of chromosomes in a basic set is called the monoploid number (x). Organisms with multiples of […]
Attenuation
Like regulation by the trp repressor, attenuation is a mechanism for reducing expression of the trp operon when levels of tryptophan are high. However, rather than blocking initiation of transcription, attenuation prevents completion of transcription. When levels of tryptophan are high, attenuation causes RNA polymerase to stop prematurely when it’s transcribing the trp operon. Only a short, stubby mRNA is made, one that does not […]
Tryptophan Operon
Operon: When a single promoter controls a number of genes. If tryptophan is present in the environment, then E. coli bacteria don’t need to synthesize it, so transcription of the genes in the trp operon is switched “off.” When tryptophan availability is low, on the other hand, the operon is switched “on,” the genes are transcribed, biosynthetic enzymes […]
Translation (Protein synthesis)
The process of protein synthesis. Charging of tRNA: Each amino acid is attached to a tRNA molecule, specific to that amino acid by a high-energy bond derived from ATP. The process is catalyzed by a specific enzyme called a synthetase (the tRNA is called charged when amino acid is attached) AA1 + tRNA1 + […]
Genetic Code
If genes are segments of DNA and if a strand DNA is just a string of nucleotides, then the sequence of nucleotides must somehow dictate the sequence of amino acids in proteins. How does the DNA sequence dictate the protein sequence? A combination of 3 nucleotides in DNA/mRNA, which specify a particular amino acid during […]
RNA splicing, the removal of introns
The vast majority of eukaryotic genes contain introns, segments of unknown function that do not code for polypeptides. Introns are present not only in protein-coding genes but also in some rRNA and even tRNA genes. Introns are removed from the primary transcript while RNA is still being synthesized and after the cap has been added, […]
Transcription in Eukaryotes
DNA replication is more complex in eukaryotes in large part because there is a lot more DNA to copy. Transcription is more complicated in eukaryotes for following reasons. The larger eukaryotic genomes have many more genes to be recognized and transcribed. Whereas bacteria usually have a few thousand genes, eukaryotes have tens of thousands of […]
Transcription
The process of formation of RNA from DNA template. The first step of information transfer from gene to protein is to produce an RNA strand whose base sequence matches the base sequence of a DNA segment, sometimes followed by modification of that RNA to prepare it for its specific cellular roles. Hence RNA is produced […]
Mechanism of DNA Replication
The process of doubling of DNA is called replication DNA REPLICATION IN PROKARYOTES Origin site: Replication starts at a single origin in the circular bacterial chromosome. The double helix opens up and both strands serve as template for the synthesis of new DNA. Gyrase: it is a type of topoisomerases and responsible for removing […]
Three-point testcross
is a cross of a trihybrid (triple heterozygote) to a triply recessive tester. This kind of cross, called a three-point testcross, is a commonly used format in linkage analysis. The goal is to deduce whether the three genes are linked and, if they are, to deduce their order and the map distances between them. Example […]