apoptosis

cell cycle checkpoints…

ensure cells can proceed to next stage of division
monitor proper division of cells
ensure that compromised cell does not continue to divide and pass on defects

3 checkpoints

g1
g2
m

g1 checkpoint

checks for cell size, nutrients, growth factors and dna damage

g2 checkpoint

checks for dna damage, dna replication accuracy and cell size

m checkpoint

checks for spindle attachment to chromosomes

cell death types

uncontrolled - necrosis
programmed and regulated (apoptosis)

necrosis

cell death that occurs as a result of trauma or injury
premature and uncontrolled
causes inflammation

apoptosis

programmed cell death through intrinsic or extrinsic pathways

why does apoptosis occur

protection - remove cells with damaged dna or that are potentially harmful
development - allows regulation of developing foetus
balance - remove cells no longer requires

initiation of apoptosis

triggered by signals initiated within the cell (intrinsic pathway) or via external signals (extrinsic pathway)

intrinsic pathway

activated by radiation of toxic chemicals damaging dna or absence of important growth factors

extrinsic pathway

activated by sigals that binds to death receptors on the membrane of target cell to be destroyed

apoptosis pathway

activated intrinsically or extrinsically
separation from adjacent cells
collapse of cells cytoskeleton
cell shrinks
breakdown of organelles
blebbing of plasma membrane
budding of plasma membrane bound vesicles
phagocytosis of dead cells