Download video slide - Universitas Airlangga

SINTESIS PROTEIN



Sri Puji Astuti Wahyuningsih
 FST UNAIR

BIODAS II Dept. Biologi FST UNAIR
ARUS INFORMASI GENETIK

Informasi DNA adalah dalam bentuk
urutan tertentu dari nukleotida di
sepanjang untai DNA

DNA diwariskan oleh organisme
◦ Menghasilkan ciri-ciri tertentu melalui sintesis
protein

Proses di mana DNA mensintesis protein
dinamakan ekspresi gen
◦ Ada dua tahapan, yaitu transkripsi dan translasi
BIODAS II Dept. Biologi FST UNAIR

RIBOSOM
◦ Adalah organel sel yang menfasilitasi terjadinya
translasi (sintesis polipeptida)
Figure 17.1
BIODAS II Dept. Biologi FST UNAIR

Konsep 1: GEN MENENTUKAN PROTEIN
MELALUI TRANSKRIPSI DAN TRANSLASI

1909, Dokter Inggris Archibald Garrod
◦ Adalah orang pertama yang menunjukkan bahwa gen
menentukan fenotip melalui enzim yang mengkatalisis
reaksi kimia tertentu dalam sel

1920, Beadle dan Edward Tatum: Neurospora crassa
(kapang roti) yang dimutasi dengan sinar-X
◦ Menciptakan mutan yang tidak bisa bertahan hidup pada
media minimal
◦ Mengembangkan hipotesis "satu gen-satu enzim“
◦ Fungsi gen adalah untuk menentukan produk enzim
tertentu
BIODAS II Dept. Biologi FST UNAIR
PRINSIP DASAR TRANSKRIPS DAN TRANSLASI

Transkripsi
◦ Adalah sintesis RNA di bawah arahan DNA
◦ Menghasilkan messenger RNA (mRNA) atau RNA
duta

Translasi
◦ Adalah sintesis polipeptida yang terjadi di bawah
arahan mRNA
◦ Terjadi dalam ribosom
BIODAS II Dept. Biologi FST UNAIR

Pada Prokariota
◦ Transkripsi dan translasi terjadi bersamaan (translasi
mRNA dimulai saat transkripsi masih berlangsung)
TRANSCRIPTION
DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
Figure 17.3a
(a) Prokaryotic cell. In a cell lacking a nucleus, mRNA
produced by transcription is immediately translated
without additional processing.
BIODAS II Dept. Biologi FST UNAIR
 Pada
Figure 17.3b
Eukariota
◦ Transkrip RNA atau transkrip primer atau pre-mRNA
dimodifikasi sebelum menjadi mRNA
Nuclear
envelope
DNA
TRANSCRIPTION
Pre-mRNA
RNA PROCESSING
mRNA
Ribosome
TRANSLATION
Polypeptide
(b) Eukaryotic cell. The nucleus provides a separate
compartment for transcription. The original RNA
transcript, called pre-mRNA, is processed in various
ways before leaving the nucleus as mRNA.
BIODAS II Dept. Biologi FST UNAIR

Aliran informasi genetik adalah
◦ DNA RNA protein

Aliran Informasi Genetik
◦ Dikodekan sebagai urutan triplet basa yang tidak
tumpang tindih yang disebut kodon
BIODAS II Dept. Biologi FST UNAIR
 Selama
transkripsi
◦ Gen menentukan urutan basa di sepanjang molekul mRNA
Gene 2
DNA
molecule
Gene 1
Gene 3
DNA strand
(template)
3
A
C
C
A
A
A
C
C
G
A
G
T
U
G
G
U
U
U
G
G
C
U
C
A
5
TRANSCRIPTION
mRNA
5
3
Codon
TRANSLATION
Protein
Figure 17.4
Trp
Phe
Gly
Ser
Amino acid
BIODAS II Dept. Biologi FST UNAIR
KODE GENETIK

Kodon dalam mRNA
Figure 17.5
Second mRNA base
U
C
A
G
UAU
UUU
UCU
UGU
Tyr
Cys
Phe
UAC
UUC
UCC
UGC
U
UUA
UCA Ser UAA Stop UGA Stop
Leu
UAG Stop UGG Trp
UUG
UCG
CUU
CUC
C
CUA
CUG
AUU
AUC
A
AUA
AUG
GUU
G GUC
GUA
GUG
Leu
lle
Met or
start
Val
CCU
CCC
CCA
CCG
ACU
ACC
ACA
ACG
GCU
GCC
GCA
GCG
U
C
A
G
U
CGU
CGC
C
Arg
CGA
A
CGG
G
U
AGU
Ser
C
AGC
A
AGA
Arg
G
AGG
Pro
CAU
His
CAC
CAA
Gln
CAG
Thr
AAU
Asn
AAC
AAA
Lys
AAG
Ala
U
GAU
GGU
Asp
C
GAC
GGC
Gly
GAA
GGA
A
Glu
GAG
GGG
G
Third mRNA base (3 end)
First mRNA base (5 end)
◦ Diterjemahkan menjadi asam amino atau berfungsi sebagai
sinyal mulai (start) dan berhenti (stop) dari translasi
BIODAS II Dept. Biologi FST UNAIR

Konsep 2: TRANSKRIPSI ADALAH SINTESIS
RNA YANG DIARAHKAN DNA
Komponen Molekular Transkripsi

Sintesis RNA dikatalisis oleh RNA polimerase.
Berfungsi untuk memisahkan untai DNA dan
menghasilkan nukleotida RNA dari arah 5’  3’

Prokariota hanya mempunyai 1 jenis RNA
polimerase. Eukatiota memiliki 3 jenis RNA
polimerase, yang digunakan untuk sintesis mRNA
adalah RNA polimerase II
BIODAS II Dept. Biologi FST UNAIR
Sintesis Transkrip RNA

Tahapan transkripsi
◦ Inisiasi
◦ Elongasi
◦ Terminasi
Promoter
Transcription unit
5
3
3
5
Start point
RNA polymerase
DNA
Initiation. After RNA polymerase binds to
the promoter, the DNA strands unwind, and
the polymerase initiates RNA synthesis at the
start point on the template strand.
1
5
3
Unwound
DNA
3
5
Template strand of
DNA
transcript
2 Elongation. The polymerase moves downstream, unwinding the
DNA and elongating the RNA transcript 5  3 . In the wake of
transcription, the DNA strands re-form a double helix.
Rewound
RNA
RNA
5
3
3
5
3
5
RNA
transcript
3 Termination. Eventually, the RNA
transcript is released, and the
polymerase detaches from the DNA.
5
3
3
5
5
Figure 17.7
Completed RNA
transcript
3
BIODAS II Dept. Biologi FST UNAIR
Pengikatan RNA Polimerase dan Inisiasi Transkripsi
TRANSCRIPTION
RNA PROCESSING
1 Eukaryotic promoters
DNA
Pre-mRNA
mRNA

Promotor : sekuen DNA
tempat melekatnya RNA
polimerase dan tempat inisiasi
untuk sintesis RNA
Ribosome
TRANSLATION
Polypeptide
Promoter
5
3
3
5
T A T A A A A
A T A T T T
T
TATA box
Start point
Template
DNA strand
Several transcription
factors
2
Transcription
factors

Faktor Transkripsi
5
3
3
5
3 Additional transcription
factors
◦ Membantu RNA polimerase
untuk mengenali sekuen
promoter pada Eukariota
RNA polymerase II
Transcription factors
5
3
3
5
5
RNA transcript
FigureFigure
17.8 17.8
Transcription initiation complex
BIODAS II Dept. Biologi FST UNAIR
Non-template
strand of DNA
Elongation
RNA nucleotides
RNA
polymerase
A
T
C
C
A
A
3
3 end
U
5
A
E
G
C
A
T
A
G
G
T
T
Direction of transcription
(“downstream”)
5
Template
strand of DNA
Newly made
RNA
BIODAS II Dept. Biologi FST UNAIR
Elongasi Transkripsi

RNA polimerase bergerak sepanjang DNA
◦ Enzim menguraikan DNA double helix, sekitar 1020 basa DNA dibuka dan dibaca untuk
menghasilkan pasangannya, yaitu nukleotida RNA
Terminasi Transkripsi

RNA polimerase telah selesai membaca DNA.
Telah dihasilkan seluruh untaian nukleotida
RNA
BIODAS II Dept. Biologi FST UNAIR

Konsep 3: SEL EUKARIOTIK MEMODIFIKASI
RNA SETELAH TRANSKRIPSI

Enzim di inti sel pada eukariotik
◦ Modifikasi pre-mRNA dengan cara tertentu
sebelum pesan genetik dikirim ke sitoplasma
BIODAS II Dept. Biologi FST UNAIR
Pengubahan ujung mRNA
Setiap ujung molekul pre-mRNA dimodifikasi
dengan cara tertentu

◦ Ujung 5 dimodifikasi dengan penambahan
nukeotida tudung (cap)
◦ Ujung 3 dengan penambahan ekor poli-A
A modified guanine nucleotide
added to the 5 end
TRANSCRIPTION
RNA PROCESSING
50 to 250 adenine nucleotides
added to the 3 end
DNA
Pre-mRNA
5
mRNA
G
Protein-coding segment
Polyadenylation signal
3
P P P
AAUAAA
AAA…AAA
Ribosome
TRANSLATION
5 Cap
5 UTR
Start codon Stop codon
3 UTR
Poly-A tail
Polypeptide
Figure 17.9
BIODAS II Dept. Biologi FST UNAIR
Split Genes dan RNA Splicing

Penyambungan RNA / RNA splicing
◦ Memindahkan intron dan menggabungkan exon
TRANSCRIPTION
RNA PROCESSING
DNA
5 Exon Intron
Pre-mRNA 5 Cap
30
31
1
Intron
Exon
Exon
3
Poly-A tail
104
105
146
Pre-mRNA
Coding
segment
mRNA
Ribosome
Introns cut out and
exons spliced together
TRANSLATION
Polypeptide
mRNA
5 Cap
1
3 UTR
Poly-A tail
146
3 UTR
Figure 17.10
BIODAS II Dept. Biologi FST UNAIR

Dilakukan oleh spliceosome, yaitu enzim yang berfungsi
untuk memindahkan intron dan menggabungkan exon
RNA transcript (pre-mRNA)
5
Intron
Exon 1
Exon 2
Protein
1
Other proteins
snRNA
snRNPs
Spliceosome
2
5
Spliceosome
components
Figure 17.11
3
5
mRNA
Exon 1
Cut-out
intron
Exon 2
BIODAS II Dept. Biologi FST UNAIR
Fungsi dan Pentingnya Intron

Adanya intron
◦ Memungkinkan satu gen dapat mengkode lebih
dari satu jenis polipeptida
BIODAS II Dept. Biologi FST UNAIR

Protein sering memiliki arsitektur modular
◦ Terdiri dari daerah struktural dan fungsional yang
disebut domain
◦ Kode exon akan berbeda untuk domain yang
berbeda pada protein
Gene
DNA
Exon 1
Intron
Exon 2
Intron
Exon 3
Transcription
RNA processing
Translation
Domain 3
Domain 2
Domain 1
Figure 17.12
Polypeptide
BIODAS II Dept. Biologi FST UNAIR

Konsep 4: TRANSLASI ADALAH SINTESIS
POLIPEPTIDA YANG DIARAHKAN OLEH RNA
Komponen Molekular Translasi

Sel mentranslasi pesan mRNA menjadi
protein dengan bantuan RNA transfer (tRNA)
BIODAS II Dept. Biologi FST UNAIR

Konsep Dasar Translasi
TRANSCRIPTION
DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
Amino
acids
Polypeptide
Ribosome
tRNA with
amino acid
attached
Gly
tRNA
Anticodon
A A A
U G G U U U G G C
Codons
5
Figure 17.13
3
mRNA
BIODAS II Dept. Biologi FST UNAIR
Struktur dan Funsi RNA Transfer

Molekul tRNA
A
◦ Tersusun dari untai RNA tunggal yang panjangnya
hanya
C
C
sekitar 80 nukleotida
3
A
Amino acid
◦ Berbentuk L
C
attachment site
(a) Two-dimensional structure. The four base-paired regions and three
loops are characteristic of all tRNAs, as is the base sequence of the
amino acid attachment site at the 3 end. The anticodon triplet is unique
to each tRNA type. (The asterisks mark bases that have been chemically
modified, a characteristic of tRNA.)
Figure 17.14a
C
A
C
G
C
U
U
A
A
U C
C A C AG
*
G
G U G U *
C
*
*
U C
* G AG
G
U
*
*
A
*
A
5
G
C
G
G
A
U
U
U
A
* C U C
C G A G
*
C
C
A
G
A
A G *
*
G
A G G
Hydrogen
bonds
C
U
G
A
Anticodon
BIODAS II Dept. Biologi FST UNAIR
Amino acid
attachment site
5
3
Hydrogen
bonds
A A G
3
Anticodon
(b) Three-dimensional structure
5
Anticodon
(c) Symbol used
in this book
Figure 17.14b
BIODAS II Dept. Biologi FST UNAIR

Enzim aminoacyl-tRNA synthetase
◦ Menggabungkan masing-masing asam amino ke tRNA
yang benar
Amino acid
P P
Aminoacyl-tRNA
synthetase (enzyme)
1 Active site binds the
amino acid and ATP.
P Adenosine
ATP
2 ATP loses two P groups
and joins amino acid as AMP.
P
Pyrophosphate
Pi
Phosphates
P
Adenosine
Pi
Pi
tRNA
3 Appropriate
tRNA covalently
Bonds to amino
Acid, displacing
AMP.
P Adenosine
AMP
4 Activated amino acid
is released by the enzyme.
Figure 17.15
Aminoacyl tRNA
(an “activated
amino acid”)
BIODAS II Dept. Biologi FST UNAIR
Ribosom
◦ Menfasilitasi ikatan antikodon tRNA dengan kodon mRNA
selama sintesis protein
DNA
TRANSCRIPTION
mRNA
Ribosome
TRANSLATION

Subunit ribosomal
◦ Disusun oleh protein
dan molekul RNA yang
dinamakan RNA
ribosomal atau rRNA
Polypeptide
Exit tunnel
Growing
polypeptide
tRNA
molecules
Large
subunit
E
P
A
Small
subunit
5
mRNA
(a)
3
Computer model of functioning ribosome. This is a model of a bacterial
ribosome, showing its overall shape. The eukaryotic ribosome is roughly similar. A
ribosomal subunit is an aggregate of ribosomal RNA molecules and proteins.
Figure 17.16a
BIODAS II Dept. Biologi FST UNAIR

Ribosom mempunyai 3 sisi pengikatan
(binding sites) tRNA
◦ Sisi P
◦ Sisi A
◦ Sisi E
P site (Peptidyl-tRNA
binding site)
A site (AminoacyltRNA binding site)
E site
(Exit site)
Large
subunit
E
mRNA
binding site
P
A
Small
subunit
(b) Schematic model showing binding sites. A ribosome has an mRNA binding site
and three tRNA binding sites, known as the A, P, and E sites. This schematic
ribosome will appear in later diagrams.
Figure 17.16b
BIODAS II Dept. Biologi FST UNAIR
Amino end
Growing polypeptide
Next amino acid
to be added to
polypeptide chain
tRNA
3
mRNA
5
Codons
(c) Schematic model with mRNA and tRNA. A tRNA fits into a binding site when its anticodon base-pairs
with an mRNA codon. The P site holds the tRNA attached to the growing polypeptide. The A site holds
the tRNA carrying the next amino acid to be added to the polypeptide chain. Discharged tRNA leaves via
the E site.
Figure 17.16c
BIODAS II Dept. Biologi FST UNAIR
Pembentukan Polipeptida

Kita dapat membagi translasi menjadi 3
tahapan
◦ Inisiasi
◦ Elongasi
◦ Terminasi
BIODAS II Dept. Biologi FST UNAIR
Asosiasi Ribosom dan Inisiasi Translasi

Tahap inisiasi translasi
◦ Menyatukan mRNA, tRNA yang membawa asam amino
pertama dari polipeptida, dan dua subunit ribosom
Large
ribosomal
subunit
P site
3 U A C 5
5 A U G 3
Initiator tRNA
GTP
GDP
E
A
mRNA
5
Start codon
mRNA binding site
1
Figure 17.17
5
3
Small
ribosomal
subunit
A small ribosomal subunit binds to a molecule of
mRNA. In a prokaryotic cell, the mRNA binding site
on this subunit recognizes a specific nucleotide
sequence on the mRNA just upstream of the start
codon. An initiator tRNA, with the anticodon UAC,
base-pairs with the start codon, AUG. This tRNA
carries the amino acid methionine (Met).
3
Translation initiation complex
2
The arrival of a large ribosomal subunit completes
the initiation complex. Proteins called initiation
factors (not shown) are required to bring all the
translation components together. GTP provides
the energy for the assembly. The initiator tRNA is
in the P site; the A site is available to the tRNA
bearing the next amino acid.
BIODAS II Dept. Biologi FST UNAIR
Elongasi Translasi
◦ Asam amino ditambahkan satu per satu ke asam amino
sebelumnya
TRANSCRIPTION
Amino end
of polypeptide
DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
mRNA
Ribosome ready for
next aminoacyl tRNA
E
3
P A
site site
5
1 Codon recognition. The anticodon
of an incoming aminoacyl tRNA
base-pairs with the complementary
mRNA codon in the A site. Hydrolysis
of GTP increases the accuracy and
efficiency of this step.
2 GTP
2 GDP
E
E
P
P
A
GDP
Figure 17.18
3 Translocation. The ribosome
translocates the tRNA in the A
site to the P site. The empty tRNA
in the P site is moved to the E site,
where it is released. The mRNA
moves along with its bound tRNAs,
bringing the next codon to be
translated into the A site.
GTP
E
P
A
A
2 Peptide bond formation. An
rRNA molecule of the large
subunit catalyzes the formation
of a peptide bond between the
new amino acid in the A site and
the carboxyl end of the growing
polypeptide in the P site. This step
attaches the polypeptide to the
tRNA in the A site.
BIODAS II Dept. Biologi FST UNAIR
Terminasi Translasi

Tahap akhir translasi adalah ketika ribosom
sampai kodon stop pada mRNA
Release
factor
Free
polypeptide
5
3
3
5
5
3
Stop codon
(UAG, UAA, or UGA)
1 When a ribosome reaches a stop 2 The release factor hydrolyzes 3 The two ribosomal subunits
codon on mRNA, the A site of the
the bond between the tRNA in and the other components of
ribosome accepts a protein called
the P site and the last amino
the assembly dissociate.
a release factor instead of tRNA.
acid of the polypeptide chain.
The polypeptide is thus freed
from the ribosome.
Figure 17.19
BIODAS II Dept. Biologi FST UNAIR
Poliribosom

Sejumlah ribosom dapat mentranslasi satu molekul
mRNA tunggal secara simultan. Hanya pada sel
prokariota
Completed
polypeptide
Growing
polypeptides
Incoming
ribosomal
subunits
Start of
mRNA
(5 end)
End of
mRNA
(3 end)
(a) An mRNA molecule is generally translated simultaneously
by several ribosomes in clusters called polyribosomes.
Ribosomes
mRNA
0.1 µm
Figure 17.20a, b
(b) This micrograph shows a large polyribosome in a prokaryotic
cell (TEM).
BIODAS II Dept. Biologi FST UNAIR
Protein Fungsional

Rantai polipeptida /protein menjalani
modifikasi setelah proses translasi
Protein dimodifikasi
- untuk membentuk molekul tiga dimensi / folding
(pelipatan)
- Untuk dapat ditranfer ke lokasi yang membutuhkan

BIODAS II Dept. Biologi FST UNAIR

Protein dibutuhkan dalam sistem
endomembran (contoh: enzim lisosim yang ada
di organel lisosom) atau disekresikan (contoh:
enzim pencernaan seperti amilase).

Protein harus ditransport ke retikulum
endoplasma (ER)
Signal peptida pada ribosom binding pada
signal-recognition particle (SRP). Kompleks
keduanya binding pada protein reseptor SRP di
ER
BIODAS II Dept. Biologi FST UNAIR

Mekanisme signal untuk protein target pada ER
1 Polypeptide
synthesis begins
on a free
ribosome in
the cytosol.
2 An SRP binds
to the signal
peptide, halting
synthesis
momentarily.
3 The SRP binds to a
receptor protein in the ER
membrane. This receptor
is part of a protein complex
(a translocation complex)
that has a membrane pore
and a signal-cleaving enzyme.
4 The SRP leaves, and
the polypeptide resumes
growing, meanwhile
translocating across the
membrane. (The signal
peptide stays attached
to the membrane.)
5 The signalcleaving
enzyme
cuts off the
signal peptide.
6 The rest of
the completed
polypeptide leaves
the ribosome and
folds into its final
conformation.
Ribosome
mRNA
Signal
peptide
Signalrecognition
particle
(SRP) SRP
receptor
CYTOSOL protein
ERLUMEN
Figure 17.21
Translocation
complex
Signal
peptide
removed
ER
membrane
Protein

Ringkasan transkripsi dan translasi pada sel eukariotik
DNA
TRANSCRIPTION
1 RNA is transcribed
from a DNA template.
3
5
RNA
transcript
RNA
polymerase
Exon
RNA PROCESSING
2 In eukaryotes, the
RNA transcript (premRNA) is spliced and
modified to produce
mRNA, which moves
from the nucleus to the
cytoplasm.
RNA transcript
(pre-mRNA)
Intron
Aminoacyl-tRNA
synthetase
NUCLEUS
Amino
acid
FORMATION OF
INITIATION COMPLEX
CYTOPLASM
AMINO ACID ACTIVATION
tRNA
3 After leaving the
4
Each amino acid
attaches to its proper tRNA
with the help of a specific
enzyme and ATP.
nucleus, mRNA attaches
to the ribosome.
mRNA
Growing
polypeptide
Activated
amino acid
Ribosomal
subunits
5
TRANSLATION
5
E
A
AAA
UGGUU UA U G
Codon
Figure 17.26
Ribosome
A succession of tRNAs
add their amino acids to
Anticodon the polypeptide chain
as the mRNA is moved
through the ribosome
one codon at a time.
(When completed, the
polypeptide is released
from the ribosome.)
BIODAS II Dept. Biologi FST UNAIR
39