•Prototrophs vs Auxotrophs
•F Factor and Conjugation
•Interrupted Conjugation Mapping
•Transformation
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Friday, August 14, 2009
Sunday, February 15, 2009
GENETIC MUTATIONS
A mutation is any permanant change in the DNA sequence. Most mutations are recognised because the phenotype, that is the characteristics displayed by an organism, have changed. There are different types of mutation. Mutations are rare events occurring at a rate of 1 in every 50 million bases added to the nucleotide chain. The rate of Mutation is 1 in10x7 cells to 1 in 10x12 cells. Most of the changes that happen are quickly repaired by our very efficient and accurate DNA repair system. But this repair mechanism is not foolproof. Failure to repair all mutations has led to the introduction of some mutations that have made organisms fitter and better able to adapt to their environments. However, many mutations have detrimental effects for an organism and it is these mutations that are the basis of many human genetic disorders and disease.
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http://www.cumc.columbia.edu/dept/ps/2007/mid/2006/MID2.pdf
Right Click and "Save" For FRANCOIS JACOB's Genetics of the bacterial cell NobelLecture,Decemberll, 1965
Right Click and "Save" For FRANCOIS JACOB's Genetics of the bacterial cell NobelLecture,Decemberll, 1965
Sunday, January 4, 2009
TRANSCRIPTION and TRANSLATION
Transcription transfers the genetic instructions from the DNA template to RNA and is the first step in expression of the genome . This highly regulated process consists of the synthesis of an RNA molecule by an RNA polymerase (RNA pol) that reads the template (or noncoding) strand of the DNA; the primary transcript will therefore carry the same genetic message as the other DNA strand, namely the coding strand.
Translation is the synthesis of a protein according to the genetic information. It is the second step of gene expression, following transcription, and is a universal and essential step for life. The process is called translation because it converts the genetic information of nucleic acid sequences, composed of four distinct nucleotides, to the polypeptide sequence composed of 20 distinct amino acids. An enzyme called aminoacyl-tRNA synthetase adds the correct amino acid to its tRNA. Amino acids are joined together in proteins by peptide bonds. This is carried out by the enzyme peptidyl synthetase. An initiation complex for translation forms by the assembly of the ribosomal subunits and initiator tRNA (met-tRNA) at the start codon on the mRNA. Several ribosomes can translate an mRNA at the same time, forming what is called a POLYSOME.
In a prokaryotic cell, transcription and translation are coupled; that is, translation begins while the mRNA is still being synthesized. In a eukaryotic cell, transcription occurs in the nucleus, and translation occurs in the cytoplasm.
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Why is transcription coupled to translation in bacteria?
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