Lecture 6 Flashcards
where do new cells come from to replenish dead ones in cellular turnover? do fully differentiated cells usually divide?
stem cells. fully differentiated cell no not normally divide (exceptions are liver hepatocytes and pancreatic beta cells)
do all cells have molecular turnover? how does this happen?
most but not all
different tissues have different rates
make new RNA, new proteins, new macromolecules and break down old ones
which cell tissue types have high rates of turnover?
those exposed to harsh environments/activities (skin, gut, blood)
what cells cannot be renewed? do they still have molecular turnover?
those with highly specialized architecture
example: sensory - photoreceptor, auditory hairs
CANNOT BE REPLACED
over time organisms loose sensory capacity
yes! still have molecular turnover
what did radio labeled leucine show in the pulse experiment about photoreceptor cells? why is this different than normal cells?
leucine incorporated into a photoreceptor protein to label it
showed that cell undergoes molecular turnover - making new proteins
normally cells break down their own proteins but this cell excreted it into layer of epithelial cells
what are stem cells (4 criteria)
- can divide indefinetely
- not terminally differentiated
- can self-renew
- child cells can differentiate
what 2 factors regulate stem cells
- internal
- external
what are the fates of daughter cells after asymmetric stem cell division?
1 stem cell (self renewal) and 1 terminally differentiated cell
what are the fates of daughter cells after symmetric stem cell division?
self renewal of both cells to 2 stem cells
what are external factors that regulate stem cell differentiation?
environment differences
what is a stem-cell niche
cells that secrete signal molecule with direct cell-cell contact that promotes stem cell self renewal, although is not a stem cell itself. if stem cell leaves niche, it will differentiate
if stem cell leaves niche, it differentiates
niche = local environment
why do stem cells have to divide very slowly and carefully (2)
protect from mutations in replication and telomere depletion
what are transit-amplifying cells
after a stem cell differentiates, divides rapidly to increase cell numbers before final differentiation
won’t stay in rapid state for long
why is a mutation in a transit-amplifying/progenitor cell not as bad as one in a stem cell
only has a few more divisions, won’t effect cells that divided before the mutation
cells in the basal-cell layer are an example of…
skin stem cell, progenitor
