Episode 54: Learn about the spectrin defect causing spherocytosis, the ubiquitination of damages intracellular constituents, different types of cells, regulation of the cell cycle, and cancer drugs.

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I. Cell Membrane Defects

A. RBC membrane defect:

Spherocytosis is a defect in spectrin within RBC cell membrane; if you can’t see a central area of pallor (if you don’t see a donut) then it’s a spherocyte. Absence of spectrin with in the RBC does not allow the RBC to form a biconcave disk; it is defective, and therefore forms a sphere.

B. Ubiquitin –

stress protein. High ubiquitin levels are associated with high levels of stress.

Some of the intermediate filaments (keratin, desmin, vimentin) are part of the superstructure of our cells (“frame of the cell”, upon which things are built). When these intermediate filaments get damaged, the ubiquitin marks then for destruction. The intermediate filaments have been tagged (ubiquinated) and marked for destruction. Some of these products have names, for example: there are open spaces within the liver tisse, these spaces are fat and they are probably due to alcohol. The ubiquinited products of the liver are called Mallory bodies. These are the result of ubiquinated filaments called keratin and these are seen in alcoholic hepatitis. Another example: Silver stain of neurofibilary tangles – Jacob crutzfelt and alzheimers dz. Tau protein is associated with neurofib tangles; this is an example of a ubiquinated neurofilament.

Example: Substantia nigra in Parkinson’s Dz – include inclusions called Lewy bodies, neurotransmitter deficiency is dopamine. Lewy bodies are ubiquinated neurofilaments. Therefore, Mallory bodies, Lewy bodies, and neurofib tangles are all examples of ubiquintation.

II. Cell Cycle–

A. Different types of cells:

1. Labile cells –

cell where the division is via a stem cell. Three tissues that has stem cells: bone marrow, basement membrane of skin, and the base of crypts in the intestine. These cells have the tendency of being in the cell cycle a lot. In pharm: there are cell cycle specific and cell cycle nonspecific drugs. The cells that are most affected by these drugs are the labile cells b/c they are in the cell cycle. Complications of these drugs are BM suppression, diarrhea, mucocidis, and rashes on the skin (there are stem cells in all these tissues!).

2. Stable cells –

in resting phase, Go phase. Most of parenchymal organs (liver, spleen, and kidney) and smooth muscle are stable cells. Stable cells can ungo division, but most of the time they are resting, and something must stimulate them to get into the cell cycle and divide – ie a hormone or a growth factor. For example: estrogen in woman will help in the proliferative phase of the menstrual cycle. The endometrial cells are initially in the Go phase and then the estrogen stimulated the cells to go into the the cell cycle. Therefore, they can divide, but they have to be invited by a hormone or a growth factor.

3. Permanent cells –

can no longer get into the cell cycle, and have been permanently differentiated. The other types of muscle cells: striated, cardiac and neuronal cells. Only muscle that is NOT a permanent tissue = smooth muscle; hyperplasia = increase in #, while hypertrophy = increase in size. Would a permanent cell be able to under hyperplasia? NO, b/c that means more copies of it. Can it go under hypertrophy? Yes. A smooth muscle cell can undergo hyperplasia AND hypertrophy.

B. Different phases of cell cycle:

1. G1 phase:

The most variable phase of cell cycle is the G1 phase. Compare with menstrual cycle: The most variable phase is the proliferative phase (not the secretory phase). The prolifertive phase varies with stress; however, once ovulation has occurred, it is 14 days. Therefore, proliferative phase is analogous to G1 phase of the cel...