GeneticsStudy of Genes 03 / 05/2012 On completion of this module you must • Define Bacterial Genetics • Understand terms used in Bacterial Genetics • Describe the structure of DNA • Describe Gene Expression in Bacteria • Describe transcription in Bacteria • Describe Translation in Bacteria ( Outline Protein synthesis steps On completion of this module you must • Understand Mutations • Describe the bacterial Genetic Transfer: • Conjugation • Transformation • Transduction What is Genetics? • The manipulation of DNA to study cellular and organismal function • DNA encodes all of the information to make the cell and the complete organism . Introduction • Single Circular DNA Material • DNA of the smallest free-living organism has a molecular weight of 5 x 108 • Bacteria are haploid • The DNA of human cells contain about 3 x 109 base pairs and can code about 1000 000 proteins . Introduction • DNA consists of 2 strands wrapped around each other I a double helix • Each strand consists of a chain of nucleotides held together by phosphates joining their deoxyribose sugar . the DNA has a directionality.Introduction • Because the phosphate joins the third carbon of one sugar to the fifth carbon of the next sugar. or polarity. and have a distinct 5` phosphate and 3` hydroxyl end . Structure of DNA • Strands(chains):Deoxyribonucleotides • A base • A sugar • A phosphate group . DNA Bases • Adenine (A) • Cytosine( C) • Thymine (T) • Guanine . DNA Bases Bases with two rings: • A and G (PURINES Bases with one ring: • T and C ( PYRIMIDINES) . DNA Bases • A third pyrimidine. replaces thymine in RNA • All four DNA bases are attached to the five-carbon sugar deoxyribose • The sugar is identical to ribose . which is found in RNA except it does not have an oxygen attached to the second carbon . uracil (U). The DNA chain • Phosphodiester bonds join deoxynucleotide link in the DNA chain . Introduction • DNA is synthesized from the precusor deoxynucleoside triphosphates by DNA polymerase • The DNA in a bacterium that carries most of the genes is called the bacterial chromosome . Mutations • A mutation is a change in the base sequence of DNA that usually results in insertion of a different amino acid into a protein and the appearance of an altred phenotype . • The organism with a mutation is called a mutant. or normal organism .Mutations • A mutation is any heritable change in the sequence of DNA of an organism. and that organism's mutant phenotype includes all the characteristics that are different from the wild-type. an AT pair) is changed into a different base pair ( e.g.g. GC pair ) .Base substitution • A mutation in which one type of base pair in DNA ( e. Missense mutations • A base pair change mutation in a region of DNA encoding a polypeptide that changes an amino acid in the polypeptide • This occurs when a base substitution results in a codon that simply causes a different amino acid to be inserted . UGA and UAA. trigger the termination of tranlation . These codons do not stipulate an amino acid in most types of organisms but. rather.Nonsense codons • Usually the codons UAG. a base pair change mutation that causes one of the nonsense codons to be encountered in frame when mRNa is translated .Nonsense mutations • In a region of DNA encoding a protein. whether or not it occurs in the coding region for a protein .Frame shift mutation • Any mutation that adds or removes one or more ( but not a multiple ) base pairs from DNA . Causes of Mutations • Chemical • Radiation • Viruses . are base analogues.group • Therefore 5-bromouracil can be iserted in place of thymine .Chemical Mutations • Some chemicals such as 5-bromouracil.the resemble normal bases • Bromine has an atomic radius similar to that of methyl. Chemical Mutations • Some chemicals. such as benzpyrene. bind to the existing DNA bases and cause frame mutations • These chemicals are often carcinogenic . found in tobacco smoke. Transfer of DNA within bacterial cell Transposon: • A DNA sequence that can move from one place in DNA to a different place with the help of transposase enzymes . some of which are only distantly related to each other .Transfer of DNA within bacterial cell • This can be done by a promiscous plasmids: • This is a self-transfmissible plasmid that can transfer itself into many types of bacteria. Transfer of DNA within bacterial cell Programmed Rearrangements: • These may be silent genes that encode variants of the antigens and the insertion of a new gene into the active site in a sequential. repeated “ programmed” manner. • These are not induced by an immune response but have the effect of allowing organisms to evade it . Conjugation • The transfer of DNA from one bacterial cell to another by the transfer functions of a self-transmissible DNA element such as a plasmid . Conjugation • Self-transmissible plasmids can transfer themselves to other bacterila cells • Mobilizable plasmids cannot transfer themselves but can be transferred by certain self-transmissible plasmids . and the cell into which the plasmid has been tranferred are called transconjugants .Conjugation • The process by which self-transmissible plasmids promote their own transfer or the transfer of other plasmids into cells is called conjugation • The original cell that contained the plasmid is the donor. Conjugation • Bacterial strains with a self-transmissible plasmid inserted into their chromosome are called Hfr strains . as well as a cis-acting oriT site at which plasmid transfer originates .Conjugation • Self-transmissible plasmids have several transacting Tra genes that encode products required for transfer. DNA is taken directly by cells .Transformation • Bacteria that are capable of taking up DNA are said to be competent • Some types of bacteria can naturally take up DNA during part of their life cycle • In transformation. Transformation • Most types of naturally transformable usually become competent only during part of their cellular growth. when they have reached high densities and are entering the stationary phase . Transformation • Some types of bacteria. including Haemophilus infleunzae and Neisseria gonorrhoea. will take up DNA of only the same species . Transduction • A process in which DNA other than phage DNA is introduced into the bacterium is introduced into bacterium by infection by a phage containing DNA . Processes leading to protein synthesis Transcription: • Is the synthesis of RNA on a DNA template • This process is probably fairly similar in all organisms. but it is best understood in bacteria • RNA is a polymer made up of a chain of ribonucleotides . Processes leading to protein synthesis • The bases of the nucleotides: • Adenine. and guanine • The enzyme responsible for making RNA is called RNA polymerase . cytosine. uracil. Translation • This is the process by which the region of mRNA encodes a protein .