1. EUKARYOTE CELL ULTRASTRUCTURE

2. Primary Cell Structure
That which can be seen using the light microscope
© P Billiet
© 2010 Paul Billiet ODWS

3. Ultrastructure
That which can be observed under the electron microscope

4. EUKARYOTE CELL ULTRASTRUCTURE
DIMENSIONS
MAIN FUNCTIONS
ORGANELLE
10 µm diameter
Cell division, protein synthesis
Nucleus
1.0 to 12.5 µm
Respiration pathways
Mitochondrion
5 to 10 µm diameter
Photosynthetic pathways
Chloroplast
0.5 to 3.0 µm diameter
Digestion, recycling & isolation
Lysosome
Cisternae: 0.5µm thick, l-3µm diameter
Secretion, reprocessing, lysosome synthesis
Golgi apparatus
26 to 56 nm thick
Support, Golgi apparatus synthesis
Endoplasmic Reticulum (ER)
20 nm diameter
Protein synthesis
Ribosome
© 2010 Paul Billiet ODWS

5. NUCLEUS (latin kernel)
TEM Nucleus of a rat hepatocyte
Image Credit:

6. NUCLEUS (pl nuclei)
10 µm
Usually spherical occupying up to 75% of the cell volume
© 2010 Paul Billiet ODWS

7. NUCLEUS Chemical composition
Protein: Up to 90%, HISTONES rich in basic amino acids.
Deoxyribonucleic Acid (DNA) about 20% (acidic)
Ribonucleic Acid (RNA) 5 to 20%
Nuclei usually contain about 10% CHROMATIN = Histone + DNA = NUCLEOPROTEIN.
© 2010 Paul Billiet ODWS

8. NUCLEUS Functions Main site of DNA in eukaryotic cells
Preservation, replication and expression of genetic information
It makes RNA for protein synthesis
It copies DNA for cell division
© 2010 Paul Billiet ODWS

9. MITOCHONDRION (gk mitos = thread khondrion = granule)
TEM of mitochondrion from mouse kidney cell
Image Credit: University of Georgia

10. MITOCHONDRION (pl. mitochondria)
outer membrane
inner membrane
Mitochondrial envelope
Inter membrane space
Cristae
Inner matrix
1.0 to 12.5 µm
© 2010 Paul Billiet ODWS

11. MITOCHONDRION Pigments Cytochromes Functions
The inner membrane contains the enzyme necessary for the synthesis of Adenosine Triphosphate (ATP)
The mitochondria are closely associated with the pathways of respiration
These metabolic pathways are divided up and supported by the membranes
© 2010 Paul Billiet ODWS

12. CHLOROPLAST (Gk chloros = green plast = form or shape)
TEM chloroplast
Image Credit: University of Wisconsin

13. CHLOROPLAST Grana Thylakoid membrane Frets outer membrane
inner membrane
Chloroplast envelope
Starch grains
Grana
Frets
Thylakoid membrane
Stroma
5 to 10 µm
© 2010 Paul Billiet ODWS

14. CHLOROPLAST Pigments Mainly chlorophylls with carotenoids and others
Function: Photosynthesis
The metabolic pathways are closely associated with the membranes as in the case of the mitochondrion
© 2010 Paul Billiet ODWS

15. Organelles and evolution
Both chloroplasts and mitochondria are double membrane bound
They involved in energy reactions
They contain extranuclear DNA and characteristic small ribosomes of their own
This has led biologists to believe that there may be some similarity in their origins in the cells of eukaryotes.
The endosymbiotic theory
© 2010 Paul Billiet ODWS

16. LYSOSOME
Image Credit:

17. LYSOSOME
Not discovered by electron microscopy but by centrifugation and enzyme analysis
Some scientists suggest that they are not present in plant cells
Structure: Simple, spherical, single membrane bound
Lysosomes contain a large number of CATABOLIC enzymes. Catabolic enzymes digest materials by hydrolysis
© 2010 Paul Billiet ODWS

18. Enzymes found in lysosomes
SUBSTRATE
Acid phosphatase
Phosphate esters
Acid ribonuclease
RNA
Acid deoxyribonuclease
DNA
Glycosidases
Polysaccharides
Protease
Proteins and peptides
Lipase
Lipids
Phospholipase
Phospholipids
More than 40 types of enzymes are known to occur in lysosomes.
© 2010 Paul Billiet ODWS

19. LYSOSOME
Function
Digestion of compounds taken in by the cell by endocytosis
Recycling of material within the cell
© 2010 Paul Billiet ODWS

20. GOLGI APPARATUS
Image Credit: International Journal of Morphology

21. GOLGI APPARATUS
Golgi vesicles transport the materials from one cisterna to the next
Cisternae are flattened sacs
Transport vesicles bring material from the endoplasmic reticulum to the entry face
Golgi vesicles take transformed materials from the exit face to their destination
© 2010 Paul Billiet ODWS

22. GOLGI APPARATUS Functions Processing and packaging
Synthesising lysosomes to contain the potentially dangerous catabolic enzymes
Producing secretory vesicles e.g. mucus
Making more plasma membrane
© 2010 Paul Billiet ODWS

23. ENDOPLASMIC RETICULUM (ER)
Image Credit:

24. ENDOPLASMIC RETICULUM (ER)
Rough ER
Smooth ER
Transport vesicles
Lumen which can occupy up to 10% of the cell volume
Membranes
© 2010 Paul Billiet ODWS

25. ER Functions
Not easy to study the ER is that it is difficult to extract intact
ER starts the biosynthetic pathways form many protein and lipid molecules in the cell
These continue in the Golgi apparatus
Rough ER has ribosomes attached to it as opposed to Smooth ER
The proteins are made on rough ER will eventually be secreted outside the cell
© 2010 Paul Billiet ODWS

26. RIBOSOME Image Credit: www.palaeos.com/
Image Credit: British Society for Cell Biology

27. RIBOSOME NOT membrane bound Found both in pro- and eukarotes
The subunits are synthesised separately in the nucleolus of the nucleus of eukaryotes
Large ribosome subunit
Small ribosome subunit
© 2010 Paul Billiet ODWS

28. RIBOSOME single free-floating attached to rough ER
Distribution in the cytoplasm
single free-floating
attached to rough ER
linked together as a POLYRIBOSOME or POLYSOME
Function: Protein synthesis
Chemical composition Protein + RNA in other words it is a nucleoprotein
© 2010 Paul Billiet ODWS

29. The relationship between organelles
Nucleus ER
Golgi apparatus
Lysosome
Ribosomes
Endocytosis
Exocytosis
© 2010 Paul Billiet ODWS