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Microbial genetics
3.1 An overview of genetic possesses3.2 The basis of hereditary3.3 DNA replication3.4 RNA and protein synthesis3.5 Gene expression
Lecture content
Genetics – science of hereditaryGenome – the genetic information of a cellChromosomes – structures containing DNA
that physically carry hereditary informationGenes – segment of DNA (except some
viruses contain RNA)Base pair – consist of A(adenine), G
(Guanine), T (thyamine) and C (cytosine)
Terminologies
3.1 An overview of genetic posesses
Crossing over
3.2 The basis of hereditary
Nucleic acid in information storage
Types of bases
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 polymeraseThe point at which the replication occur are called
as replication fork
DNA replication
DNA replication (Eukaryote)
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
DNA replication (Prokaryote)
RNA and protein synthesisTranscription and translation
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
Overal process of RNA and protein synthesis
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’
Transcription process
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
Traffic light of transcription
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
Translation process
Sense codon – code for amino acidNonsense codon – also called as stop codon,
will stop the translation process
Types of codon
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
Reasons behind translation
Genetic control mechanismsRepression
Induction
The Operon Model of 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
Regulation of bacterial gene expression
Repression Inhibits gene expression and decreases the
synthesis of enzymesPrevent from overbundance of an end
product of metabolic pathwayThe protein use to decrease the rate is known
as repressorIt has ability to block RNA polymeraseThe default position of repressible gene is on
Induction Turns on the transcription of a gene The substance involve known as inducerThe enzyme that are synthesized in the
present of inducer are inducible enzymesEg. Enzyme β-galactosidase that split lactose
to glucose and galactose for E.coli
The Operon Model of gene expressionIntroduce by Francois Jacob and Jacques
Monod in 1961To account the regulation of protein
expressionGene that determined the surface of protein
is known as structural genesIn lac operon, there are two short DNA
segment known as promoter and operator
Terminologies Promoter – region of DNA where RNA
polymerase initiate transcriptionOperator – as a traffic light that instruct the
structural genes to be transcribedOperon – consist of operator, promoter and
three structural genes
System of the Operon
Operon on and off
The end