1. Kompartemen intraseluler Regulasi PROTEIN pascatranslasi
SISTEM ENDOMEMBRAN
Kompartemen intraseluler
Regulasi PROTEIN pascatranslasi

2. Components of the endomembrane system:
Concept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell
Components of the endomembrane system:
Nuclear envelope
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Vacuoles
Plasma membrane
These components are either continuous or connected via transfer by vesicles
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3. Nuclear envelope

4. The Endoplasmic Reticulum: Biosynthetic Factory
The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells
The ER membrane is continuous with the nuclear envelope
There are two distinct regions of ER:
Smooth ER, which lacks ribosomes
Rough ER, with ribosomes studding its surface
For the Cell Biology Video ER and Mitochondria in Leaf Cells, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

5. Smooth ER Nuclear envelope Rough ER ER lumen Cisternae Transitional ER
Fig. 6-12
Smooth ER
Nuclear envelope
Rough ER
ER lumen
Cisternae
Transitional ER
Ribosomes
Transport vesicle
200 nm
Smooth ER
Rough ER
Figure 6.12 Endoplasmic reticulum (ER)

6. Functions of Smooth ER The smooth ER Synthesizes lipids
Metabolizes carbohydrates
Detoxifies poison
Stores calcium
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

7. Functions of Rough ER The rough ER
Has bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates)
Distributes transport vesicles, proteins surrounded by membranes
Is a membrane factory for the cell
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

8. The Golgi Apparatus: Shipping and Receiving Center
The Golgi apparatus consists of flattened membranous sacs called cisternae
Functions of the Golgi apparatus:
Modifies products of the ER
Manufactures certain macromolecules
Sorts and packages materials into transport vesicles
For the Cell Biology Video ER to Golgi Traffic, go to Animation and Video Files.
For the Cell Biology Video Golgi Complex in 3D, go to Animation and Video Files.
For the Cell Biology Video Secretion From the Golgi, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

9. (“receiving” side of Golgi apparatus) 0.1 µm
Fig. 6-13
cis face
(“receiving” side of Golgi apparatus)
0.1 µm
Cisternae
Figure 6.13 The Golgi apparatus
trans face
(“shipping” side of Golgi apparatus)
TEM of Golgi apparatus

10. Lysosomes: Digestive Compartments
A lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules
Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids
Animation: Lysosome Formation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

11. A lysosome fuses with the food vacuole and digests the molecules
Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole
A lysosome fuses with the food vacuole and digests the molecules
Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy
For the Cell Biology Video Phagocytosis in Action, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

12. Fig. 6-14
Nucleus
1 µm
Vesicle containing
two damaged organelles
1 µm
Mitochondrion
fragment
Peroxisome
fragment
Lysosome
Digestive
enzymes
Lysosome
Lysosome
Plasma
membrane
Peroxisome
Figure 6.14a Lysosomes
Digestion
Food vacuole
Mitochondrion
Digestion
Vesicle
(a) Phagocytosis
(b) Autophagy

13. Vacuoles: Diverse Maintenance Compartments
A plant cell or fungal cell may have one or several vacuoles
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14. Video: Paramecium Vacuole
Food vacuoles are formed by phagocytosis
Contractile vacuoles, found in many freshwater protists, pump excess water out of cells
Central vacuoles, found in many mature plant cells, hold organic compounds and water
Video: Paramecium Vacuole
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

15. Central vacuole Cytosol Nucleus Central vacuole Cell wall Chloroplast
Fig. 6-15
Central vacuole
Cytosol
Nucleus
Central vacuole
Figure 6.15 The plant cell vacuole
Cell wall
Chloroplast
5 µm

16. Kompartemen intraseluler Regulasi PROTEIN pascatranslasi
SISTEM ENDOMEMBRAN
Kompartemen intraseluler
Regulasi PROTEIN pascatranslasi

17. Polyribosomes
A number of ribosomes can translate a single mRNA simultaneously, forming a polyribosome (or polysome)
Polyribosomes enable a cell to make many copies of a polypeptide very quickly
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

18. Completed polypeptide Growing polypeptides Incoming ribosomal subunits
Fig
Completed
polypeptide
Growing
polypeptides
Incoming
ribosomal
subunits
Polyribosome
Start of
mRNA
(5 end)
End of
mRNA
(3 end)
(a)
Ribosomes
Figure Polyribosomes
mRNA
(b)
0.1 µm

19. Completing and Targeting the Functional Protein
Often translation is not sufficient to make a functional protein
Polypeptide chains are modified after translation
Completed proteins are targeted to specific sites in the cell
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

20. Protein Folding and Post-Translational Modifications
During and after synthesis, a polypeptide chain spontaneously coils and folds into its three-dimensional (3D) shape
Proteins may also require post-translational modifications before doing their job
Some polypeptides are activated by enzymes that cleave them
Other polypeptides come together to form the subunits of a protein
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

21. Protein Folding
Figure 6–84 Co-translational protein folding.

22. Protein Folding Figure 6–86 The Hsp70 family of molecular chaperones.
Figure 6–87 The structure and function of the Hsp60 family of molecular chaperones.

23. Targeting Polypeptides to Specific Locations
Two populations of ribosomes are evident in cells: free ribsomes (in the cytosol) and bound ribosomes (attached to the ER)
Free ribosomes mostly synthesize proteins that function in the cytosol
Bound ribosomes make proteins of the endomembrane system and proteins that are secreted from the cell
Ribosomes are identical and can switch from free to bound
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

24. Polypeptide synthesis always begins in the cytosol
Synthesis finishes in the cytosol unless the polypeptide signals the ribosome to attach to the ER
Polypeptides destined for the ER or for secretion are marked by a signal peptide
A signal-recognition particle (SRP) binds to the signal peptide
The SRP brings the signal peptide and its ribosome to the ER
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

25. Ribosome mRNA Signal peptide ER membrane Signal peptide removed
recognition
particle (SRP)
Protein
CYTOSOL
Translocation
complex
ER LUMEN
SRP
receptor
protein
Sintesis protein pada REK:
Translasi protein berawal di sitosol.
Peptida sinyal (20-25 residu AA hidrofobik pada N-terminal) diikat oleh SRP.
SRP berikatan dengan reseptor RSP (protein penambat/docking protein) yang ada di membran REK, menambatkan ribosom ke REK.
SRP dilepaskan dan sintesis protein dilanjutkan.
Polipeptida mengalami elongasi (nascent polypeptide) masuk ke dalam lumen REK dan peptida sinyal dilepaskan.
Sintesis protein selesai, nascent polypeptide dilepaskan ke lumen REK, unit translasi terdisosiasi.
Figure The signal mechanism for targeting proteins to the ER

26. Overview: Protein trafficking
Nucleus
Rough ER
Smooth ER
cis Golgi
Figure 6.16 Review: relationships among organelles of the endomembrane system
Plasma membrane
trans Golgi

27. Modifikasi protein pada Retikulum Endoplasma
Penambahan gugus fungsional tertentu pada protein.
Figure 6–82 Steps in the creation of a functional protein.

28. To be continue… Take home activity
Modifikasi protein pada RE
Sortasi protein sekresi pada apparatus Golgi
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