operon concept b. sc. iii

7/23/2019 Operon Concept B. Sc. III

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Operon Concept

Dinesh D. KhedkarDepartment of Botany

NAAC Reaccredited “A” - “Very Good” Grade

Shri Shivaji Science College A College with Potential for Excellence (CPE)

Amravati, Maharashtra - 444 603Phone No.: 0721-2660855 Fax: 0721-2665485

e-mail : [email protected] We si!e : """.dinesh#hed#a$."es.com



All geneticists are not in agreement withthese defnitions o gene, howeverollowing defnition o gene may serve

our purpose.

"The gene of function is thesequence of nucleotides

(providing numerous sites forintragenic mutation andor/recombination) whichs ecies the amino acid

!O#$% &#%#



'hat is &ene A gene is a segment o nucleic acid that contains

the inormation necessary to produce a

unctional product, usually a protein. Genesconsist o a long strand o DNA (NA in some

viruses! that contains egulatory "e#uences (apromoter, which controls the activity o a gene,

and a coding se#uence, which determines whatthe gene produces!.



&hat is Gene 'Genes are polynucleotides. )ach nucleotide is

made up o a *ase group, a sugar and one

phosphate group $he sugar group orms the *ack*one o DNA. $hephosphate group are responsi*le or linking onenucleotide to another. $he nitrogenous *ases o

nucleotides ace each other and orm +ydrogen*onds with their complimentary *ases.



O#$O%* + T,# -.*C CO%C#T O0$O1.$2OTC &#%# $#&34.TO%

egulated genes can *e switchedon and o depending on the cell-smeta*olic needs

perona regulated cluster oad/acent structural genes, operatorsite, promotor site, and regulatorygene(s)



O#$O%

Structural genegene that codes or apolypeptide

Promoter regioncontrols access to the

structural genes, located *etween thepromoter and structural genes, contains theoperator site.

Operator Site region where the repressor

attaches Regulatory genescodes or repressor

proteins

Polycistronic mRNAtranscript or severalpolypeptides



4.C O#$O%

Regulator Promoter Operator Lac Z Lac Y Lac A

BPs +/- 111 - 35 -26 0 3063 800 800

Peptide

Am!o ac" 360 1021 2#5 2#5

$% &'a( 3800 1)25)000 30)000 30)000

Active

Protein *etramer *etramer $o!omer 'mer

Function Repressor β- Galactosidase Permease Trans acetylase

egulator Gene

egulatory

"e#uence

"tructural Genes



)0)""123) 4". 1ND5%123) 0)N" $& $60)" 7 N)GA$14) G)N) )G53A$1N

epressi*le perons

Genes are initially

ON Ana*olic pathways

)nd product

switches o its ownproduction

1nduci*le perons

Genes are initially

OFF %ata*olic pathways

"witched on *y

nutrient that thepathway uses



LAC5 .% %3C-4# O#$O%



.% #6.!4# O0 O*T7#&#%# $#&34.TO%8C.!



#31.$2OTC &#%#O$&.%9.TO%

e!a!cers

sle!cers



$+) %N$3 7 G)N))80)""1N



$AN"%10$1NA3 )G53A$1N 41A %+9A$1N9D171%A$1N

DNA methylationmethyl groups addedto cytosineinactivate genes

+istone acetylation %%+: added to

amino acids. educe *inding *etweenDNA and histoneconse#uence'

TRANSCRIPTION INITITION



%N$3 A$ $+) $AN"%10$1NA33)4)3

Transcription Factorsaugmenttranscription *y *inding to DNA or toeach other. Act as repressors and

activators.

Coordinately controlled genesusually

associated with a specifc regulatoryse#uence and activated or repressed*y the corresponding transcription

actor



Opportunities for te control of !ene e"pression in te eu#aryotic

cell



Example:The metallothionein (!T:) gene

Te metallotionein protein protects te cell a!ainst

e"cess concentrations of eavy metals$ %y %indin! te

metal and removin! it from te cell& Te !ene is e"pressed

at a %asal level$ %ut is induced to !reater levels of

e"pression %y eavy metal ions 'suc as cadmium( or %y!lucocorticoids&



$+) "$5%$5) 7 %+9A$1N

DNA comple;ed withprotein ormschromatin

diuse duringinterphase

condensed duringmitosis, ormschromosomes

histones andnucleosomes



$+) "$5%$5) 7 %+9A$1N 2ased on successive levels o DNA

packing



$60)" 7 %+9A$1N

Heterochromatin> +ighly

condensedduringinterphase, not

actively

transcri*ed

uchromatin>

3ess condensed

duringinterphase,a*le to *e

transcri*ed



Re!ulation of !ene e"pression at te level of cromatin

,eue!ce-!"epe!"e!t

l!.er sto!es co!trol 'A compacto! a!" accesslt to trans-act!g actors

post-tra!slato!al mo"cato!s o sto!e tals co!trol compacto! o 'A a!"

ser4e as "oc.!g stes or tra!s-act!g actors

Ra!ge a! act at te le4el o a s!gle ge!e) ote! acts o4er groups o ge!es a!"o4er larger "oma!s &20-200.() a!" ca! aect ge!e epresso! o4er a! e!tre

cromosome



$+) %D) 2)6ND G)N)$1%" 1NDNA

$he original code is that each codonspecifes a particular amino acid andsu*se#uent protein

$he second code is determined *y theplacement o the nucleosomes.

Nucleosomes protect and controlaccess to the DNA



N5%3)"9)"

:?,???,??? nucleosomes in eachhuman cell

DNA wraps @.B times around anucleosome

$he DNA twist is @C *ase pairs

$he average DNA strand contains <<Bmillion *ase pairs

9ade o proteins called histones



+& D N5%3)"9)"75N%$1N'

2ind to the DNA at specifc se#uences

0revent transcription actors romattaching and initiating transcription

Nucleosomes can and do move, lettingDNA open to *e transcri*ed. +ow'

This has not yet *een determined!



$AN"%10$1N 1N1$1A$1N

Diversity o NA 0olymerase

$%. ol 4ocation roduct

1 Nucleolus rNA

11 Nucleoplasm Nuclear NA

111 Nucleoplasm $ E small NA



NA 0369)A") F 1

$wo part promoter

@. %ore 0romoter CB to <?

<. 5pstream control )lement @@? to @?

@. 5%) (5pstream %ontrol )lem! and 520

<. $20 ($ata 2inding 7actor!



$A$A 28

<B *p 5pstream o the start point

I *p %onsensus se#uence entirely oA$

$end to *e surrounded o G% richregion

"ingle *ase mutation acts as a strong

down mutation NA 0ol F 11 initiate at this point

$A$A 2inding 0rotein ($20! (:?,??? Da!and $20 Associated 7actors ($A7! orms



$A$A 28

$20 is a commitment actor working orpositioning NA 0ol.

2inding in &ide Groove

9utation in $A$A 2o; leads to erraticinitiation

2ound to J @? *p



3& TFII1 4

RNA Pol%indin!• %inds to TFII/•

1inds to RNAPol 2it TFIIF



%AA$ 28

3ocated at B to F I? 5pstream

%onsensus "e#uence

7unctions in either orientation

2ound to J << *p

1ts inclusion leads to increase promoterstrength

%$7 and N7@ are the assisting actors

: 3acs =cell



$+) G)N)$1% 2A"1" 7



$+) G)N)$1% 2A"1" 7D)4)309)N$

7rom single cell to multicellular

organism

Dierential gene e;pression

Genetic and cellular mechanisms opattern ormation



79 "1NG3) %)33 $ 953$1%)3353A GAN1"9

1nvolves cell division, morphogenestis andcell dierentiation

Cell division5 increases cell num*ers

Morphogenesis: overall shape o theorganism is esta*lished

Cell diferentiation5 cells *ecomespecialiHed in structure and unction

evelopment has been studied using

model organisms



D177))N$1A3 G)N) )80)""1N

Dierent types o cells in an organismhave the same DNA

0lants are totipotent , cells retain thea*ility o the Hygote to give rise to alldierentiated cells

Animals are not as plastic, alternativeapproaches used, nuclear

transplantations such as LDollyM



D)$)91NA$1N

Dierent cell types make dierentproteins

ole o transcription regulation

$wo sources o cellular instructions ordetermination>

cytoplasmic determinants and

neigh*oring cells



+& G)N)" %N$3 D)4)309)N$(G)N)$1% ANA36"1" 7 "ROSOPH#$A!

evealed roles o specifc moleculesthat direct position and dierentiation

Cytoplasmic determinants provide

postional inormation (unertiliHedeggs> orientation o anteriorposteriorand dorsalventral already determined!

@<?? genes essential or development,@<? in segmentation



3) 7 GAD1)N$" 7 9A$)NA3 93)%53)"

+ypothesiHed over @?? years ago %icoid &ene essential or development o

the anterior o a y, produces mNA that

concentrates in anterior hal ounertiliHed eggs.

7emale ies w=out this gene produce

em*ryos lacking ront hal o em*ryo 2icoid protein regulate other genes, a

domino like eect



',.T * . ,O!#O-O6

O"ince their discovery in @I:,homeo*o; genes, and the proteins theyencode, the homeodomain proteins,

have turned out to play important rolesin the developmental processes omany multicellular organisms. &hile

certainly not the only developmentalcontrol genes, they have *een shownto play crucial roles rom the earlieststeps in em*ryogenesis

*e omeoo 7as org!all "escre" as a



*e omeoo 7as org!all "escre" as a

co!ser4e" 'A mot o aout 180 ase pars

*e prote! "oma! e!co"e" te omeoo) te

omeo"oma!) s tus aout 60 am!o ac"s lo!g

*e rst ge!es ou!" to e!co"e omeo"oma!

prote!s 7ere 'rosopla "e4elopme!tal co!trol

ge!es) ! partcular omeotc ge!es) rom 7c te!ame 9omeo9o 7as "er4e"

:o7e4er) ma! omeoo ge!es are !ot omeotc

ge!es; te omeoo s a seue!ce mot) 7le9omeotc9 s a u!cto!al "escrpto! or ge!es tat

cause omeotc tra!sormato!s9



"599A6

$hus, one can say that thehomeodomain is a DNA*inding domainthat occurs in proteins that are usually

transcription actors. $hesetranscription actors regulate thetranscription o other genes and hence

very re#uently play important roles indevelopment o multicellularorganisms.



*O!# #0%TO%*

,o; genes> +o; genes are a su*groupo homeo*o; genes. 1n verte*ratesthese genes are ound in gene clusters

on the chromosomes. 1n mammals oursuch clusters e;ist, called +o; clusters.

$he gene name O+o;O has *een

restricted to name +o; cluster genes inverte*rates. nly genes in the +8cluster should *e named +o; genes. "onote> homeo*o; genes are N$ +o;

,O6 C43*T#$>



,O6 C43*T#$>

$he term +o; cluster reers to a group o

clustered homeo*o; genes, named +o; genesin verte*rates, that play important roles inpattern ormation along the anteriorposterior*ody a;is.

1n act, the frst homeo*o; genes discoveredwhere those o the Drosophila homeotic geneclusters, i.e. the OAntennapedia comple;O andthe O2ithora; comple;O, which summarily arereerred to as +9% (homeotic comple;!. $his+9% comple; in Drosophila is theevolutionary homolog o the verte*rate +o;

clusters and the evolutionarily related



homeodomain> a DNA*indingdomain, usually a*out ? amino acidsin length, encoded *y the homeo*o;.

homeobo;> a ragment o DNA oa*out @I? *asepairs (not counting

introns!, ound in homeo*o; genes.

3) 7 N)1G+21NG %)33"



3) 7 N)1G+21NG %)33"1ND5%$1N

"ignaling help coordinate spatialand temporal e;pression o genes

se#uential inductions control organormation

results in selective activation andinactivation o genes within target

cells

A00$"1" 0GA99)D %)33



A00$"1"0GA99)D %)33D)A$+

LsuicideM genes product presentcontinuously

depends upon regulating proteinactivity

tadpole tail'

Degenerative diseases, cancersaulty

$+) 93)%53A 213G6 7



$+) 93)%53A 213G6 7%AN%)

Genetic changes thataect the cell cycle(viruses,carcinogens!

Oncogenecancercausing gene

Protooncogenesnormally code orregulatory proteinscontrolling cellgrowth, division, and

adhesion

$+) 93)%53A 213G6 7



$+) 93)%53A 213G6 7%AN%)

esult o genetic changes

can *e random

can *e caused *y viruses or

carcinogens Oncogenes* cancer causing genes ormed rom protooncogenes *y

DNA movement within the genomePgene amplifcation, or point mutations changes in tumorsuppressor genes



0$N%G)N)"N%G)N)"

9ovement o DNA within the genome Gene amplifcation

0oint mutation

"ometimes suppressor genes thatnormally inhi*it growth can *eresponsi*le or cancer



953$103) 95$A$1N" 5ND)31) $+) D)4)309)N$7 %AN%)

@BQ due to viruses "omatic mutations ( B@?Q o *reast

cancer!



0"$$AN"%10$1NA3



0"$$AN"%10$1NA39)%+AN1"9"

Regulation o+ mRNA degradation> severalhours or even weeks

Protein processing and degradation>activation may re#uire addition ophosphate groups or sugarsP use o signalse#uencesP marking or destruction

Control o+ translation> inactivation oinitiation actors, use o repressor proteins

0"$$AN"%10$1NA3



0"$$AN"%10$1NA39)%+AN1"9"

9ay *e stopped or enhanced at anyposttranscriptional step

ole o the nuclear envelope

Regulation o+ mRNA degradation several hours toseveral weeks

Control o+ translation inactivation o initiationactors, use o repressor proteins

Protein processing and degradationmay re#uireaddition o sugars or phosphatesP use o signal

se#uencesP marking or destruction

operon concept b. sc. iii

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