categories which is spontaneous mutation is not caused by mutagen example is errors in during gene expression and as a result of a natural radiation alters the structure of bases in the DNA and induced mutation is caused by chemical or physical agents.
Type of mutation have two types which is point mutation and frameshift mutation. Point mutation is base substitutions at one point in the DNA or RNA sequence. Three types of point mutation which is silent mutation, nonsense mutation and missense mutation. Silent mutation is genetic code is degenerate or redundant because a single amino acid may be coded for by more than one codon and not all mutation in protein-encoding genes result in changes in protein. Silent mutation is almost always occur in the third base of a codon (except, arg and leu- at first base). Missense mutations is changes in first or second base lead to significant changes in protein and instead of the original amino acid in the polypeptide chain, a different one is substituted. Nonsense mutations is results from stop codon (UAG, UAA, UGA) formation, change from codon for an amino acid (sense codon) to a stop codon (nonsense codon) and termination of translation. Frameshift mutation is genetic code is read from one end in conservative blocks of 3 bases, mutations that add or remove a base shift the reading frame of the genetic message results in a totally different protein from the point of mutation. Most likely to get termination of protein synthesis soon after the mutation. Type of mutagen is base analogues, chemical mutagens, radiation and intercalating agents. Identifying mutants is detection by selecting or testing for an altered phenotype. Two kind of identifying mutant which is selectable or nonselectable. Nonselectable is loss of colour in pigmented organism. Selectable is drug resistance; an antibiotic-resistant mutant can grow in the presence of antibiotic concentrations that inhibit or killed the parent.
On Friday, Dr Suriana taught us about the gene recombination. Genetic Recombination is exchange of genes between two DNA molecules and forms new combination of genes on a chromosome. Types of Genetic Transfer which is vertical gene transfer and horizontal gene transfer. Vertical gene transfer is occurs during reproduction, between generations of cells. Horizontal gene transfer is transfer of genes between cells of the same generation. Mechanisms of Horizontal Transfer Genes are naturally transferred between bacteria using three mechanisms which is transformation, transduction and conjugation. Transformation is transfer of naked DNA from one bacterium to another, works best when donor and receipt are closely related and recipient has to be competent. Competence is the ability of a cell to receive naked DNA from its environment which is alterations in the cell wall that make it permeable to large NDA molecules and some bacteria are naturally competent but some have to undergo treatment to make it competent. Two types of competent which is natural competence and artificial competence . Discovered by Fredrick Griffith in 1928 while working with Streptococcus pneumoniae. Transduction is the bacterial DNA transferred from donor to recipient via bacteriophage. Bacterial DNA is incorporated into bacteriophage. Two types of transduction which is generalized is any bacterial genes are transferred and specialized is specific regions of DNA are transferred.
Conjugation requires direct contact between cells. Types of contact is Gram negative is the sex pili and Gram positive is the sticky surface molecule. Mediated by plasmids can code for traits that give bacteria advantage. Plasmid types is fertility factor, dissimilation plasmids, resistance factor, bacteriocin factor and virulence plasmids. 2 kinds which is Plasmid transfer and Chromosome transfer. Plasmid transfer is F+ donor contains F plasmid is F - recipient cells do not contain F plasmid and sex pilus is formed.Oone strand of DNA is transferred into the recipient cell from the donor cell and F - become F +. Chromosome transfer is when F plasmid is integrated into the chromosome, an Hfr cell is formed. Hfr has high frequency recombinant during conjugation, an Hfr cell can transfer chromosomal DNA into the recipient cell (F- ) is usually the chromosome breaks before it is fully transferred. F - become recombinant F- cell. Transposons is small segments of DNA that can move from one region of a chromosome to another region of the same chromosome or to a different chromosome or DNA molecule is found in chromosomes, plasmids, viruses. It has simple to complex structures and can carry any type of gene, including antibiotic resistance genes that cause mutations which is increase (or decrease) the amount of DNA in the genome.
No comments:
Post a Comment