dasar2 genetika (ekspresi gen)

7/27/2019 Dasar2 Genetika (Ekspresi Gen)

http://slidepdf.com/reader/full/dasar2-genetika-ekspresi-gen 1/24

EKSPRESI GEN &PENGENDALIANNYA

1



2

Ekspresi gen dan mekanisme

pengendaliannya

A. Operon dan regulonB. Pengendalian pasca transkripsi

C. Pengendalian pasca translasi dan modifikasi

proteinD. Pengendalian global dan sinyal transduksi



Dari Gen ke Protein

3



Ekspresi Gen

4



Animasi Translasi

5

http://c/Documents%20and%20Settings/Biotek%202006/Lecture%207%20-%208/Translation.mov

http://c/Documents%20and%20Settings/Biotek%202006/Lecture%207%20-%208/translation.swf

http://c/Documents%20and%20Settings/Biotek%202006/Lecture%207%20-%208/translation1.swf

http://c/Documents%20and%20Settings/Biotek%202006/Lecture%207%20-%208/protein_synthesis.swf

http://c/Documents%20and%20Settings/Biotek%202006/Lecture%207%20-%208/micro06.swf

http://c/Source%20Molecular/SWF/DNA%20SWF/transcribe-translate.swf



Regulasi Gen pada Bakteri

• Bakteri mempunyai beribu-ribu gen

– Tidak semua ditranskripsi pada waktu yang sama

– Bila itu dilakukan maka akan membuang energiyang banyak

– Namun beberapa gen ditranskripsi sepanjangwaktu Siapa dia ?

• “housekeeping” genes

– Gen lain diekspresikan sebagai tanggapan(respon) akibat terjadinya perubahan lingkungan

6



Regulasi Gen pada Bakteri

• Regulasi transkripsi

– Jika suatu protein (yang dikodekan oleh gen)

diperlukan, maka gen akan ditranskripsi – Jika suatu protein (yang dikodekan oleh gen)

Tidak diperlukan, maka gen akan Tidak akan

ditranskripsi

7



Unit Transkripsi pada Bakteri

8

Operon

promoter

operator

-35 TTGACA

-10 TATAAT (Pribnow box)



Regulasi pada Transkripsi

• Kontrol Positif atau Negatif

– Positif - membutuhkan suatu protein untuk

terjadinya transkripsi – Negatif - protein dibutuhkan untuk mem block

transkripsi

• Model operon pada bakteri

– Lac operon

9



Regulasi Lac operon

• Merupakan Kontrol Negatif

• Repressor protein (lac I gene product)

• Berikatan pada operator region dari Lac operon

• Mencegah terjadinya proses transkripsi

10



Induksi repressed operon

11

o

(can’t bind) (lac repressor)

(allolactose)



Regulasi Lac operon

• Repressor berikatan pada operator

– TIDAK terjadi transkripsi

• Effector berikatan pada Repressor – Repressor tidak dapat berikatan dengan operator

– Terjadi Transkripsi

• Berkurangnya konsentrasi Effector

– Repressor akan bebas untuk berikatan denganoperator

– TIDAK terjadi transkripsi

12



Regulasi Lac operon

• Satu gen yang berekspresi dari lac operon

– b-galactosidase

– Memecah laktosa (dan allolactose) menjadiglukosa dan laktosa

13

LACTOSE

(allolactose)

(effector)

Glucose

&

Galactose

b-gal



Repressi Operon Bakteri

14

co-repressor (tryptophan)Repressor

complex

Biosynthetic

Operons(Trp Operon)



Aktivasi & Deaktivasi Operon

15

Activator

effector inactive

complex



Regulasi Transkripsi Eukariotik

• Beberapa gen ditranskripsi pada hampir semua sel

– “housekeeping” genes

• Sifat unik dari sel itu disebabkan oleh ekspresi gen-

gen spesifik yang terkandung dalam sel tersebut

– cell-specific expression – tissue-specific expression

16




• Kemampuan untuk aktivasi dan penekanan

gen menjadi bagian yang esensial untuk

memelihara kespesifikan sel

17

skin

hepatocyteneuron




• Lebih kompleks dibanding bakteri

• Pengendalian dimediasi oleh protein-protein

yang diklasifikasikan sebagai TranscriptionFactors - TF :

– Basal TF - diperlukan oleh semua gen

– Specific TF - menentukan spesifitas ekspresi

– Activator - meningkatkan ekspresi

– Repressor - menurunkan ekspresi

18



Skema Promoter Gen Eukariot

19

Hampir semua mempunyai TATA box pada -25

Posisi TF binding sites lebih upstream“GC box” “CCAAT box” etc.

SP1 TFIID



Penerapan

• Merekayasa promoter yang berbeda di

depan coding sequences yang diinginkan,

dapat menghasilkan:

20

a. Regulasi yang berbeda

b. Meningkatkan laju ekspresi

c. Mengubah waktu ekspresid. Ekspresi terjadi di jaringan yang berbeda

e. Ekspresi pada organisme yang berbeda



Animasi Regulasi

21

Operon Lac

Eukariotik Control Expr. Operon

http://c/Documents%20and%20Settings/parasitologi/Gambar/Lac%20Operon.mov

http://c/Source%20Molecular/SWF/DNA%20SWF/micro_operons.swf

http://c/Source%20Molecular/SWF/Cloning%20SWF/Bio110prokregulation.swf

http://c/Source%20Molecular/SWF/Cloning%20SWF/bio31%20Control%20gene.swf

http://c/Source%20Molecular/SWF/Cloning%20SWF/bio27%20Operon%20Lac.swf



Signal Transduksi

22



• signal transduction refers to any process by which a cell converts one kind ofsignal or stimulus into another, most often involving ordered sequences ofbiochemical reactions inside the cell, that are carried out by enzymes, activated bysecond messengers resulting in what is thought of as a "signal trandusctionpathway". Such processes are usually rapid, lasting on the order of milliseconds inthe case of ion flux, minutes for the activation of protein and lipid mediated kinasecascades, or hours and days in terms of gene expression. In many signaltransduction processes, the number of proteins and other molecules participatingin these events increases as the process emanates from the initial stimulus,resulting in a "signal cascade" and often results in a relatively small stimuluseliciting a large response. This is referred to as amplification of the signal.

• In bacteria and other single-cell organisms, the variety of a signal transduction aprocesses of which the cell is capable influences how many ways it can react andrespond to its environment. In multicellular organisms, a multitude of differentsignal transduction processes are required for coordinating the behavior ofindividual cells to support the function of the organism as a whole. As may beexpected, the more complex the organism, the more complex the repertoire ofsignal transduction processes the organism must possess. Thus, sensing of boththe external and internal environment at the cellular level, relies on signaltransduction. Many disease processes such as diabetes, heart disease,autoimmunity and cancer arise from defects in signal transduction pathways,

further highlighting the critical importance of signal transduction to biology as wellas medicine.

23

http://en.wikipedia.org/wiki/Signal_%28biology%29

http://en.wikipedia.org/wiki/Cell_%28biology%29

http://en.wikipedia.org/wiki/Biochemistry


http://en.wikipedia.org/wiki/Chemical_reaction

http://en.wikipedia.org/wiki/Enzyme

http://en.wikipedia.org/wiki/Second_messenger






http://en.wikipedia.org/wiki/Biochemical_cascade


http://en.wikipedia.org/wiki/Bacterium

http://en.wikipedia.org/wiki/Organism

http://en.wikipedia.org/wiki/Multicellular_organisms


http://en.wikipedia.org/wiki/Sense


http://en.wikipedia.org/wiki/Diabetes

http://en.wikipedia.org/wiki/Atherosclerosis

http://en.wikipedia.org/wiki/Autoimmunity

http://en.wikipedia.org/wiki/Cancer











http://en.wikipedia.org/wiki/Organism

http://en.wikipedia.org/wiki/Bacterium






http://en.wikipedia.org/wiki/Signal_%28biology%29

http://en.wikipedia.org/wiki/Cell_%28biology%29



24