Download Microbial genetics

 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
 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)
 Process where one parental of double stranded DNA will
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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
Transcription 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
 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’
 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
 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
 Sense codon – code for amino acid
 Nonsense codon – also called as stop codon, will stop
the translation process
 Transfer RNA (tRNA) – will recognize the specific codon
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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
Repression
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
 Inhibits gene expression and decreases the synthesis of
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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
 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
 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 lac operon, there are two short DNA segment
known as promoter and operator
 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