1. Organelles of Eukaryotic Cells
AHMP 5406

2. Objectives
List the principle functions and describe the structure of the nucleus, mitochondrion, endoplasmic reticulum, Golgi, lysosomes and peroxisomes in higher eukaryotes
Describe the modification and transport of proteins from the ER through the Golgi
Describe the intracellular transport of proteins from the trans Golgi network to lysosomes
Describe the structure of the mitochondrion and the process of ATP synthesis
Describe the contribution of organellar dysfunction to the development of disease

3. Basic eukaryotic organelles
Nucleus
Endoplasmic reticulum (ER)
Golgi
Peroxisomes
Lysosomes
Mitochondria

4. General eukaryotic cell

5. How molecules are transported around the cell…

6. The Nucleus

7. Nucleus The largest organelle in eukaryotes
Surrounded by 2 phospholipid bilayers
Inner nuclear membrane defines the nucleus itself
Outer nuclear membrane is continuous with the rough ER
Space between the inner and outer membranes is continuous with the lumen of the rough ER

8. Nucleus
The two nuclear membranes fuse at the nuclear pores which regulate movement of molecules between nucleus and cytosol
Contains the DNA of eukaryotic cells
DNA is packaged into chromosomes in metabolically active nuclei (growing or differentiating cells)
The cell’s rRNA is synthesized in the nucleolus (a suborganelle)

9. Nucleus

10. How molecules are transported around the cell…

11. The nucleus

12. The nucleus

13. The nucleus

14. Ran GTPases drive directional transport through nuclear pore complexes
Ran is a molecular switch
Two conformations
dependent on what is bound to it
Ran-GEF is in the nucleus
GDP to GTP
“Cocks the hammer”
Creates a gradient
Ran-GAP is in the cytosol
GTP to GDP
Uses energy to import
“pulls the trigger”

15. The Endoplasmic Reticulum

16. Endoplasmic reticulum
Second largest cellular organelle
Has many functions, but primarily important in the synthesis of membrane lipids and proteins
Two types: rough and smooth

17. Smooth Endoplasmic reticulum
Functions in synthesis of fatty acids and phospholipids
Abundant in hepatocytes
enzymes in SER detoxify hydrophobic chemicals such as pesticides and carcinogens to water soluble compounds that can be excreted
High doses of these compounds result in LOTS of SER proliferation

18. Rough Endoplasmic reticulum
Ribosomes bound to the surface make it “rough”
Responsible for synthesis membrane and organellar proteins and virtually all proteins that are to be secreted from the cell
Ribosomes that make these proteins are bound to the ER by the newly growing peptide chain
The newly made protein passes through the RER with the help of specific proteins
These new proteins accumulate in the lumen of the RER and await transport
Very abundant in cells that produce secreted proteins: plasma cells (antibodies), pancreatic acinar cells (digestive enzymes)

19. Endoplasmic reticulum

20. Endoplasmic reticulum

21. Endoplasmic reticulum

22. How the endoplasmic reticulum probably came to be…

23. The Golgi Complex

24. Golgi Responsible for protein modification and transport
Divided into the cis-, medial and trans- Golgi
Transfer vesicles from the ER fuse with the cis- region and deposit proteins
After movement through the Golgi, they bud off through the trans- side

25. Golgi

26. Golgi

27. Transport of proteins from trans-Golgi to lysosomes
Lysosomal hydrolases carry a maker
Mannose 6-phosphate (M6P)
M6P groups are recognized by M6P receptor proteins in trans-Golgi
Bind to lumenal side by way of adaptins
Adaptins interact with clathrin molecules on the cytosolic side
Shuttled to late endosome where pH change releases hydrolase

28. Peroxisomes

29. Peroxisomes Contain oxidases – enzymes that generate hydrogen peroxide
Large amounts of catalase – degrades hydrogen peroxide to water and oxygen
Oxidation is NOT linked to ATP generation
Produce acetyl groups that are used in the production of cholesterol and biosynthetic molecules in animal cells
Also degrade toxins produced by liver, kidney cells, etc.

30. Peroxisomes

31. Peroxisome-assembly related diseases
X-linked adrenoleukodystrophy (ADL)
Defective oxidation of very long chain fatty acids
ADL gene encodes the peroxisomal membrane protein that transports an oxidative enzyme into the peroxisomes
Effects are evident in mid-childhood: severe neurological disorders followed by death within a few years

32. Peroxisome-assembly and function related diseases
Pseudo-Zellweger syndrome
Beta-oxidation disorder (fatty acid metabolism)
Other peroxisomal functions remain intact
Symptoms are present at birth
Major body systems are affected: vision, kidneys, cartilage, heart, muscle and liver

33. Lysosomes

34. Lysosomes Acidic organelles – pH4.8
Contain degradative enzymes (acid hydrolases): nucleases, proteases, phosphatases, etc.
Can degrade intracellular components, phagocytized or endocytized items
May be several hundred in a typical animal cell
Degrade themselves by autophagy

35. Lysosomes

36. Lysosomes

37. Lysosomal Storage Diseases
Caused by genetic defects
Result in accumulation of undigested substrates in lysosomes
Usually act on nervous system
Hurler’s syndrome
Caused by mutation on gene that codes for enzyme that breaks down glycosaminoglycan
Results in deformation and retardation
I-cell disease
Severe form of Hurler’s syndrome
Detected by inclusion bodies in tissue cells
Cell hydrolases are misdirected and secreted

38. Tay Sachs Disease
1 in 27 Jews in the U.S. are carriers of the defective Hex-A gene
Frequency in the general population is 1 in 250
Over 50 DNA mutations have been identified in the Hex-A gene
DNA testing is usually done in conjunction with biochemical testing for Hex-A levels in the blood

39. Tay Sachs Disease
Individuals are lacking the ability to break down gangliosides (glycolipids)
Symptoms usually appear before age 1
Children become blind and demented by age 2
Usually fatal by age 3
Nerve cells are greatly enlarged with swollen, lipid-filled lysosomes

40. How molecules are transported around the cell…

41. Mitochondria

42. Mitochondria Up to 25% of cytoplasm volume Main site of ATP production
Inner and outer membrane
Outer membrane allows molecules up to 10,000 mw to pass through, much like gram negative bacteria
Inner membrane is composed of cristae that function to increase oxidative surface area

43. Mitochondria Fuels for ATP synthesis are fatty acids and glucose
Degradation of 1 glucose to CO2 and H2O can yield up to 36 ATP molecules
Initial stage producing 2 ATPs’ occurs in the cytosol
Terminal stages producing up to 34 ATP’s are carried out by mitochondrial enzymes in the matrix and cristae

44. Mitochondria

45. How the mitochondrion probably came to be…

48. Summary Points
All eukaryotic cells contain a membrane bound nucleus and organelles in their cytosol
Lysosomes, which are found only in animal cells, have an acidic interior and contain various hydrolases used to break down cellular components
Peroxisomes are small organelles containing enzymes that oxidize various organic compounds, generating hydrogen peroxide

49. Summary Points
Mitochondria are bound by two membranes, the inner one extensively folded. Enzymes in the inner mitochondrial membrane and central matrix carry out the terminal stages of sugar and lipid oxidation coupled to ATP synthesis
Secretory and membrane proteins are synthesized on the RER (a network of membrane vesicles studded with ribosomes). These proteins move to the Golgi complex where they are stored and processed

50. Summary Points
The nucleus is surrounded by an inner and an outer membrane. Movement of molecules into and out of the nucleus occurs through the nuclear pores. The outer nuclear membrane is continuous with the RER.
The cytosol is the portion of the cell’s interior that remains after you take away all of the organelles. There are a lot of proteins in it – lots of soluble enzymes, actin microfilaments, microtubules and intermediate filaments. These help to give the cell some sort of structure.

51. General eukaryotic cell