1. Department of Cancer and Cell Biology
Principles of Cell Biology for Engineers I: Cell Specialization and Multicellular Structures
Sarah Pixley
Univ. of Cincinnati
College of Medicine
Department of Cancer and Cell Biology

2. Cell Specialization and Multicellular Structures
How do you get a “specialized” cell, a cell of a tissue or organ?
Express proteins that the typical cell does not express! OR
Express MORE of certain typical proteins!

3. Cells expressing “New” Proteins
i.e. Neurons

4. Neurons Neuron-specific proteins:
Control electrical activity of the cell membrane
Aid in making long processes and filling the processes
Allow neurons to talk to each other and to muscles via special connections and chemical signals (neurotransmitter substances)
Longest cells in body! One CELL goes from your neck to your toe!! (much > 30 µm!) 1 meter?
But the processes are only about 30 µm wide!

5. Cells expressing “MORE” of a typical protein
Muscle: (Especially skeletal muscle) is packed with huge amounts of mostly two “movement” proteins, found at some level in every cell:
Actin
Myosin

6. Muscle Cell is
Packed with
Long polymers
Of actin +
myosin

7. Multicellular Organization
Cell Biology: Study of the “typical” cell and “specialized” cells
Tissues: Specialized cells of similar shape and function
Organs: A collection of one or more tissues that forms a unit that is specialized for one function
(often even textbooks confuse tissue+organ!)

8. Multi-cellular Organization: Tissues
Four types of tissues:
1. Epithelia (single: epithelium)
2. Connective Tissues
3. Muscle
4. Nervous Tissue

9. Tissues-1: Epithelia
Epithelia (singular: epithelium): Cells (performing a similar function) that are tightly attached to each other and have little extracellular matrix between them.
Examples:
Skin (epidermal layer)
The lining of the digestive and respiratory tracts
Linings on the outside of all your major organs

10. GENERALIZED EPITHELIUM

11. Tissues-2: Connective Tissues
Tissues containing cells that are not attached as extensively as in epithelia, and which have extensive amounts of extracellular fluid or materials (extracellular matrix) between them.
Examples:
Blood
Bone
Dermis of the skin

12. Bone is a connective tissue:

13. Bone Cells
Osteoblasts (bone forming cells) make osteoid (collagen + other proteins) and
bury themselves in it! The osteoid then gets calcified, (mineralized), trapping the
now-mature osteocyte inside. Osteocytes live in lacunae, connected to other cells by
canaliculi. Osteoclasts (bone breakdown cells) remove bone, releasing calcium
into blood.

14. Bone http://depts.washington.edu/bonebio/bonAbout/histo/histo.html
If you zoom in, you can see a red stripe in some places next to the bone. The dyes make proteins red. This is OSTEOID, which is newly formed collagen that does not have any calcium in it yet

15. Bone Cells respond to Physical Forces!
It has been known since the 1800s that the thin pieces of bone in the marrow of long bones (called trabeculae), line up precisely along the physical stress lines. Bone cells respond to physical forces and put down bone exactly along force lines. How? Another area of research!
Carter, Orr,+ Fyhrie, J. Biomechanics (1989) 22:231

16. Blood slides thanks to L. M. Parysek, Ph.D., UC

17. ERYTHROCYTES (Red Blood Cells)
RBCs can squeeze through the smallest blood vessels in our body: capillaries.

18. Normal RBCs
RBC’s should have:
Normal size
Normal color
Normal shape

19. Abnormal RBCs: sickle cell disease
Abnormalities of RBC shape due to an abnormality in hemoglogin
Abnormal RBCs:
sickle cell disease
Sickle cells
Anemia from hemolysis

20. In a clot, blood cells become enmeshed in a fibrin network
derived from fibrinogen
RBC
RBC

21. Platelets
aka thrombocytes, are cell fragments, 2-3 m in diameter, and function in blood clotting

22. When platelets are activated, they change shape
Platelet activation →
Unactivated platelets
The veil and filopodia

23. Platelets become activated to participate in clot formation
Activation
Activated platelets in a clot

24. Not only do platelets change shape to participate in clot formation, they also release their granule contents to enhance clot formation and dissolution