1. Endomembrane system and vesicular transport

2. Figure 4.7 Eukaryotic Cells (Part 1)

3. The Endomembrane System
The endomembrane system includes many membranous compartments in the cell )primarily the ER and golgi
Has many roles and activities. Most are related to
Export from the cell or import into the cell.

4. The Endomembrane System
The endoplasmic reticulum (ER) is a network of interconnecting membranes distributed throughout the cytoplasm.
The internal compartment, called the lumen, is a separate part of the cell with a distinct protein and ion composition.
The ER’s folding generates a surface area much greater than that of the plasma membrane.
At certain sites, the ER membrane is continuous with the outer nuclear envelope membrane.

5. The Endomembrane System

6. The Endomembrane System
The rough ER (RER) has ribosomes attached.
The smooth ER (SER) is a ribosome-free region of the ER.
Cells that are specialized for synthesizing proteins for extracellular export have extensive ER membrane systems.

7. Protein synthesis in cytoplasm
Many proteins are synthesized in the cytoplasm on “free” ribosomes and are targeted to the relevant site after synthesis
Mature protein stays in cytosol or sent to:
Nucleus,
Mitochondria,
Peroxisome,
Etc.

8. Protein synthesis on ER membrane
Some proteins are synthesized on ER (RER) membrane

9. Protein synthesis on ER membrane
ER proteins are tranlocated to the ER while being synthesized
Protein synthesis on ER

10. Protein synthesis on ER membrane
Signal sequence halts protein synthesis until the ribosome is loaded onto the membrane

11. Protein synthesis on ER membrane
ER proteins are tranlocated to the ER while being synthesized

12. Protein synthesis on ER membrane
ER proteins are tranlocated to the ER while being synthesized

13. Synthesis of membrane proteins
Start & stop signals determine protein arrangement in the membrane

14. Protein glycosylation in the ER lumen
An oligosaccharide is often added onto proteins in the ER.
This modification is called glycosylation and is important in directing proteins to their correct site.

15. The Endomembrane System
The rough ER (RER) has ribosomes attached.
The site of protein synthesis and chemical modification (disulfide bridges, addition of carbohydrate groups to glycoproteins), folding into tertiary structure
Cells that are specialized for synthesizing proteins or lipids for extracellular export have extensive ER membrane systems.
The smooth ER (SER) is a ribosome-free region of the ER.
Chemical modification of proteins; chemical modification of small molecules (drugs, pesticides); hydrolysis of glycogen; synthesis of lipids and steroids
Most Lipid biosynthesis is in ER
Liver cells, which modify molecules that enter the body from the digestive system, have abundant smooth ER

16. The Endomembrane System
Rat liver cell

17. The Endomembrane System
Misfolded proteins are retained in the ER and folding is assisted by Chaperons.

18. The Endomembrane System
The ER is dynamic and is constantly changing
ER Dynamics

19. Vesicular transport
Proteins and membranes are further shuttled from the ER by vesicular transport
protein secretion

20. The Endomembrane System
The Golgi apparatus consists of flattened membranous sacs and small membrane-enclosed vesicles.
The Golgi apparatus has three roles:
Receive proteins from the ER and further modify them.
Concentrate, package, and sort proteins before they are sent to their destinations.
Some polysaccharides for plant cell walls are synthesized.

21. The Endomembrane System
Secreted proteins are released from cells by constitutive or regulated exocytosis

22. The Endomembrane System
Content of vesicle includes:
Soluble proteins
Membrane
Membrane proteins

23. Vesicular transport
Vesicle content is controlled
Docking of vesicle depends on target

24. Vesicular transport
Exocytosis – outward vesicular transport
Endocytosis – inward vesicular transport
Nucleus

25. Phagocytosis
Endocytosis is inward vesicular transport
Phagocytosis of large particles is performed by specialized cells
Uptake of molecules and fluids is Pinocytosis

26. Endocytosis
Endocytosis

27. Endocytosis
Endocytosis

28. Figure 4.13 Lysosomes Isolate Digestive Enzymes from the Cytoplasm

29. Lysosomes
Lysosomes are vesicles containing digestive enzymes that come in part from the Golgi.

30. Lysosomes
Lysosomes are sites for breakdown of food and foreign material brought into the cell by phagocytosis.
Lysosomes are also the sites where digestion of spent cellular components occurs, a process called autophagy.

31. Lysosomes
Tay-sachs Disease (severe degeneration of brain cells)
Tay Sachs is a Glycosphingolipid (GSL) Storage Disease caused by the absence of hexoseaminidase A which is required for the complete digestion of the lipid GM2

32. Lysosomes
A different mechanism causing Tay-sachs is incorrect protein trafficking

33. Endocytosis
Receptor mediated endocytosis and sorting
DVD

34. Vesicular transport
Vesicle content is controlled
Docking of vesicle depends on target

35. Vesicular transport
Vesicle budding is driven by the assembly of a protein coat
Clathrin coated pits

36. Figure 5.16 Formation of a Coated Vesicle (Part 1)

37. Figure 5.16 Formation of a Coated Vesicle (Part 2)

38. The Endomembrane System
Exo and endocytosis

39. Endocytic pathway of the LDL and its receptor
The Low Density Lipoprotein (LDL) particle carries cholesterol in the blood stream
Endocytic pathway of the LDL and its receptor

40. Endocytic pathway of the LDL and its receptor
Proton
Pump

41. Receptor mediated endocytosis
The LDL-receptor has a molecular address that directs its incorporation into clathrin coated pits

42. Formation of clathrin coated pits
Ligand
Receptor
Adaptin
Signal
sequence
Clathrin

43. A single point mutation in the endocytic signal of the LDL receptor was diagnosed in patient with familial hypercholesterolemia
Diseases caused by hampered receptor-mediated endocytosis

44. The mutant receptor does not internalize LDL

45. Viruses
Most viruses are composed of a nucleic acid and a few proteins.
Viruses are acellular (noncellular) and do not metabolize energy.
Viruses do not produce ATP or conduct fermentation, cell respiration, or photosynthesis.
Viruses can reproduce only in systems that do perform these functions: living cells.
Viruses that infect bacteria are called bacteriophage.

46. Viruses: Reproduction and Recombination
Outside the cell Virus particles are called Virions
Virion genetic material is either DNA or RNA and is generally surrounded by a capsid, or protein coat.
Characteristic shapes are determined by the protein coat.
Viruses are unaffected by antibiotics because they lack the cell wall structure and ribosomal biochemistry of bacteria.

47. Figure 13.4 The Reproductive Cycle of the Influenza Virus (Part 2)

48. Viruses: Reproduction and Recombination
Retroviruses (HIV) are RNA viruses that can integrate into cellular chromosomes
Reverse transcriptase converts viral RNA to DNA
A large portion of many genomes is composed of remnants of retroviral like elements

49. Figure 13.5 The Reproductive Cycle of HIV (Part 2)

50. Figure 13.5 The Reproductive Cycle of HIV (Part 2)
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