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

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!

Cells expressing “New” Proteins i.e. Neurons

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!

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

Muscle Cell is Packed with Long polymers Of actin + myosin

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!)

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

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

GENERALIZED EPITHELIUM

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

Bone is a connective tissue:

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. http://www.womentowomen.com/bonehealth/natureofhealthybones.aspx?id=19&campaignno=bonehealth&adgroup=ag8cells&keywords=bone+cells

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 http://depts.washington.edu/bonebio/bonAbout/histo/histo.html

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

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

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

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

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

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

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

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

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

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