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Microbial genetics. Lecture content. 3.1 An overview of genetic possesses 3.2 The basis of hereditary 3.3 DNA replication 3.4 RNA and protein synthesis 3.5 Gene expression. Terminologies . Genetics – science of hereditary Genome – the genetic information of a cell
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Lecture content • 3.1 An overview of genetic possesses • 3.2 The basis of hereditary • 3.3 DNA replication • 3.4 RNA and protein synthesis • 3.5 Gene expression
Terminologies • Genetics – science of hereditary • Genome – the genetic information of a cell • Chromosomes – structures containing DNA that physically carry hereditary information • Genes – segment of DNA (except some viruses contain RNA) • Base pair – consist of A(adenine), G (Guanine), T (thyamine) and C (cytosine)
DNA replication • Process where one parental of double stranded DNA will split into 2 daughters dsDNA • The copies are exactly the same and doesn’t involve in protein production • There will be free-nuclotides that available surround the cells that permits the replication process • At this time, the new stands will copy it oppositely as pairing the bases in parental DNA, A with T and C with G, from 5’ to 3’, will be copied as 3’ to 5’ • The process where induce by DNA polymerase • The point at which the replication occur are called as replication fork
The new daughter DNA will have one old strand and one newly replicate DNA and this is called as semiconservative replication • In special case like in some bacteria, E. coli, the process is bidirectionally around the cromosome. • There will be 2 forks move oppositely away from the origin of replication
RNA and protein synthesis Transcription and translation
Transcription • Synthesis of a complementary strand of RNA from DNA template • As your know, there are three RNA in bacterial cell: messenger RNA, ribosomal RNA and transfer RNA • Ribosomal RNA (rRNA) – integral component in ribosome producing protein • Messenger RNA (mRNA) – carries the coded information for making specific proteins from DNA to ribosomes
Transcription process • In transcription, the mRNA strands will copy the specific strands in DNA template • The component of nucleic acid bases will be produce in the mRNA pairing the bases in DNA template, for example, a G with C, via versa • However in RNA, there are no T so they replace it with U that will be paired with A • the DNA strand have 3’ and 5’ ends, so mRNA strand will start copy the bases oppositely, example if the DNA strand start from 3’ and end with 5’, 3’ – ATGCCTA – 5’, the mRNA will start copy and producing 5’ and end up with 3’, 5’ – UACGGAU - 3’
Traffic light of transcription • The transcription process can only occur with present of RNA polymerase enzyme and supply of RNA nucleotides • The process begins when RNA polymerase binds to the DNA at site called promoter • The transcription continues until the RNA polymerase reaching the site in DNA called terminator • mRNA will become a intermediate storage of DNA information before the translation process take place
Translation process • Translating the ‘language of nucleic acid’ to the ‘language of protein’ • ‘language’ of mRNA is in the form of codons, 3 nuclotides consider as 1 codon and coded for 1 specific protein, eg. UAG, GCC, UGG • There are 64 possiblity of codon but only 20 types of amino acid are synthesize • It is due to the degeneracy situation where some protein coded by more than 1 codon
Types of codon • Sense codon – code for amino acid • Nonsense codon – also called as stop codon, will stop the translation process
Reasons behind translation • Transfer RNA (tRNA) – will recognize the specific codon and transport the particular amino acid • tRNA has an anticodon which are used to read the codon in the mRNA strands • Most probably the sequence in tRNA now are similar with the origin strand (DNA template) • Basically in the DNA genes itself compose of exon (seq that expressed) and introns (seq that do no encode protein) • All the introns will be removed by small nuclear ribonucleoproteins ( snRNPs) and combine all the exons together
Genetic control mechanisms Repression Induction The Operon Model of Gene Expression
Regulation of bacterial gene expression • Most of microbial metabolic reaction need enzymes • Some enzymes are needed in a big amount through out the bacterial life as a living demands, for example the glucose product (enzymes of glycolysis) • In other cases, the enzyme where only needed in a particular amount and that is why the operon system present
Repression • Inhibits gene expression and decreases the synthesis of enzymes • Prevent from overbundance of an end product of metabolic pathway • The protein use to decrease the rate is known as repressor • It has ability to block RNA polymerase • The default position of repressible gene is on
Induction • Turns on the transcription of a gene • The substance involve known as inducer • The enzyme that are synthesized in the present of inducer are inducible enzymes • Eg. Enzyme β-galactosidase that split lactose to glucose and galactose for E.coli
The Operon Model of gene expression • Introduce by Francois Jacob and Jacques Monod in 1961 • To account the regulation of protein expression • Gene that determined the surface of protein is known as structural genes • In lacoperon, there are two short DNA segment known as promoter and operator
Terminologies • Promoter – region of DNA where RNA polymerase initiate transcription • Operator – as a traffic light that instruct the structural genes to be transcribed • Operon – consist of operator, promoter and three structural genes
