Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                
SlideShare a Scribd company logo

5.ER - cell biology

•
•
mohammad mir mohammadi
mohammad mir mohammadi

The endoplasmic reticulum (ER) is a large organelle that helps process and transport proteins within cells. It has two main domains: the rough ER, where proteins are synthesized, and the smooth ER, where lipids are produced. Newly synthesized proteins enter the ER through translocon channels in the membrane. In the ER, proteins undergo modifications like folding, disulfide bond formation, glycosylation, and lipid additions to help them mature and prepare for transport to other organelles like the Golgi apparatus via transport vesicles. Integral membrane proteins are inserted into the ER membrane through translocon complexes and can span the membrane multiple times. The ER plays a key role in protein sorting and transport within eukaryotic cells

1 of 20
Download to read offline
Cell BiologyCell Biology S. Rahgozar,PhD University of Isfahan Faculty of Science 4. Protein sorting and transport 4.1. The Endoplasmic Reticulum 1392-93
The Endoplasmic Reticulum  The largest organelle in most eukaryotic cells  ER membrane is 50% of cell membrane  Space enclosed by ER is 10% of the total cell volume
 ER domains:  Rough ER (+ ribosomes)  Smooth ER where lipid metabolism happens  Transitional ER where vesicles exit to the Golgi apparatus
 Isolation of rough ER Rough ER Folding Processing Golgi apparatus Sorting Processing Transport Secretory vesicles Inside Outside
 Overview of protein sorting Golgi apparatus
 The secretory pathway Pancreatic cell
 Incorporation of secretory proteins into cytoplasm/microsomes  The signal sequence of growth hormone 20 hydrophobic amino acid proceeded by a basic aa (ie; Arg) N
 Cotranslational targeting of secretory proteins to the ER SRP: signal recognition particle Translocon: membrance channel
Structure of the SRP Blue: SRP proteins Orange: SRP RNA including 2 flexible hinge regions Green: Signal sequence The signal sequence on the nascent protein binds to a pocket in the SRP proteins
Translocons are  Complexes of 3 membrane proteins called the Sec61 proteins  Conserved among prokaryotic and eukaryotic cells Signal sequence Short hydrophobic side chains in translocon neck Opening of the translocon channel Transfer of the growing polypeptide chain through the translocon
 Translocation of proteins into the ER after their translation HSP 70 BIP acts as a ratchet to drive the posttranslational translocation of proteins into the ER.
 Insertion of proteins into the ER membrane Integral membrane proteins span the membrane via α-helical regions of 20 to 25 hydrophobic amino acids, which can be inserted in a variety of orientations.
 Transport of integral membranes Proteins destined for the inner nuclear membrane do not transfer by vesicles, but move laterally in the plane of the membrane. Transport vesicle
 Insertion of integral proteins o Insertion of a membrane protein with a cleavable signal sequence and a single stop-transfer sequence
o Insertion of a membrane protein with no cleavable signal sequence ? Orientation of the protein depends on the orientation of the signal sequence
o Insertion of a protein that spans the membrane multiple times
 Transport of integral membranes Proteins destined for the inner nuclear membrane do not transfer by vesicles, but move laterally in the plane of the membrane. Transport vesicle Specific tansmembrane sequences located in the inner nuclear membrane proteins may alter their interaction with the translocon and signal their transport to the inner nuclear membrane where they are retained by interactions with nuclear components such as lamins or chromatin
 Types of post translational modification of proteins in the ER o Protein folding in the ER o Formation of disulfide bonds (S-S) Formation of S-S bonds is facilitated by PDI , the enzyme which is located in the ER lumen.
o Glycosylation 14 sugar residues 3 Asn-X-Ser/Thr Oligosaccharyl transferase Glycoslation  Helps to prevent protein aggregation  Provides signals for subsequent sorting in the secretory pathway 9
o Addition of glycoprotein phosphatidyl inositol (GPI) anchor Yellow: inositol Red: mannose Blue: Glucosamine Purple: N- acetylgalactosamine

More Related Content

5.ER - cell biology

  • 1. Cell BiologyCell Biology S. Rahgozar,PhD University of Isfahan Faculty of Science 4. Protein sorting and transport 4.1. The Endoplasmic Reticulum 1392-93
  • 2. The Endoplasmic Reticulum  The largest organelle in most eukaryotic cells  ER membrane is 50% of cell membrane  Space enclosed by ER is 10% of the total cell volume
  • 3.  ER domains:  Rough ER (+ ribosomes)  Smooth ER where lipid metabolism happens  Transitional ER where vesicles exit to the Golgi apparatus
  • 4.  Isolation of rough ER Rough ER Folding Processing Golgi apparatus Sorting Processing Transport Secretory vesicles Inside Outside
  • 5.  Overview of protein sorting Golgi apparatus
  • 6.  The secretory pathway Pancreatic cell
  • 7.  Incorporation of secretory proteins into cytoplasm/microsomes  The signal sequence of growth hormone 20 hydrophobic amino acid proceeded by a basic aa (ie; Arg) N
  • 8.  Cotranslational targeting of secretory proteins to the ER SRP: signal recognition particle Translocon: membrance channel
  • 9. Structure of the SRP Blue: SRP proteins Orange: SRP RNA including 2 flexible hinge regions Green: Signal sequence The signal sequence on the nascent protein binds to a pocket in the SRP proteins
  • 10. Translocons are  Complexes of 3 membrane proteins called the Sec61 proteins  Conserved among prokaryotic and eukaryotic cells Signal sequence Short hydrophobic side chains in translocon neck Opening of the translocon channel Transfer of the growing polypeptide chain through the translocon
  • 11.  Translocation of proteins into the ER after their translation HSP 70 BIP acts as a ratchet to drive the posttranslational translocation of proteins into the ER.
  • 12.  Insertion of proteins into the ER membrane Integral membrane proteins span the membrane via α-helical regions of 20 to 25 hydrophobic amino acids, which can be inserted in a variety of orientations.
  • 13.  Transport of integral membranes Proteins destined for the inner nuclear membrane do not transfer by vesicles, but move laterally in the plane of the membrane. Transport vesicle
  • 14.  Insertion of integral proteins o Insertion of a membrane protein with a cleavable signal sequence and a single stop-transfer sequence
  • 15. o Insertion of a membrane protein with no cleavable signal sequence ? Orientation of the protein depends on the orientation of the signal sequence
  • 16. o Insertion of a protein that spans the membrane multiple times
  • 17.  Transport of integral membranes Proteins destined for the inner nuclear membrane do not transfer by vesicles, but move laterally in the plane of the membrane. Transport vesicle Specific tansmembrane sequences located in the inner nuclear membrane proteins may alter their interaction with the translocon and signal their transport to the inner nuclear membrane where they are retained by interactions with nuclear components such as lamins or chromatin
  • 18.  Types of post translational modification of proteins in the ER o Protein folding in the ER o Formation of disulfide bonds (S-S) Formation of S-S bonds is facilitated by PDI , the enzyme which is located in the ER lumen.
  • 19. o Glycosylation 14 sugar residues 3 Asn-X-Ser/Thr Oligosaccharyl transferase Glycoslation  Helps to prevent protein aggregation  Provides signals for subsequent sorting in the secretory pathway 9
  • 20. o Addition of glycoprotein phosphatidyl inositol (GPI) anchor Yellow: inositol Red: mannose Blue: Glucosamine Purple: N- acetylgalactosamine