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Lecture 15

BIOL 355 Lecture 15: Lecture 15

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University of Waterloo
BIOL 355
Dr.Cheryl Duxbury

Lecture 15 Theories of Aging Hayflick limit Cells will divide and reproduce only a limited number of times cell clock Number is genetically programmed limitations Programmed aging: validation by tissue culture Could the biological clock be within each cell Cultured cell findings Is cellular aging programmed or random event? Cultured cells from skin tissue Divide a finite of times Cultured cells mortal Aging must occur from inside the cell Cells grown in vitro have demonstrated they have a fixed number of times they can divide. This is called the Hayflicks limit Defined as the number of times cells in culture can replicated before they stop dividing and die Population Doubling and Hayflicks Limit What do we mean by the term doubling and how are cells cultured in vitro? One serial passage or population doubling of cells Population doubling is literally going from one culture plate in which the cells are completely covering the bottom to 2 dishes, then 4 then 8 then 16 That is why is is called doubling It is a doubling of the cultures and not the cells themselves In vitro Hayflicks findings: Cells from fetal tissue are capable of about 50 population doublings then lose ability to divide further in vitro About 50 doublings then number of cells begins to decrease and eventually the cells die (incapable of doubling further in vitro) Cell count stays constant at around 1 million until 50 serial passages in tissue cultreu then they begin to die and cell count starts to decrease Phase 1 ; 13 weeks Period of adjustments for cells Primary culture terminates with the formation of te first confluent sheet Phase II Vigorous growth
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