programmed cell death - cells between fingers/toes die

• 1/2 of neurons created never make connections, eventually die
• required for proper development
• necrosis - cells that die due to injury, releases contents into extracellular fluid
• apoptosis - cell programmed to die shrink/shrivel, remains taken up by other cells
• bax proteins starts apoptosis by binding to permeable pores of mitochondria
• bcl-2 prevents cell death by preventing damange from free radicals (highly reactive atomic fragments)
• antioxidants - proteins, other molecules that destroy free radicals

aging theories - puberty is safest time to live 

• accumulated mutation hypothesis - oldest general theory about aging
  • accumulation of mutations >> lethal death
  • OH group tends to be added to guanine base as cells age
  • effects of radiation-induced mutations after Hiroshima/Nagasaki bombings show no correlation between aging and mutations
• telomere depletion hypothesis - older cells have shorter telomeres
  • telomere - repeated TTAGGG sequence
  • portion of telomere cap lost w/ each replication
  • cancer cells avoid telomeric shortening
  • adding to telomeric caps increased number of times cells could perform DNA replication
• wear-and-tear hypothesis - cells wear out, get damaged through age
  • damage over time limits cell’s ability to work properly
  • free radicals - atomic fragments containing an unpaired electron, produced by oxidative metabolism, can damage cells
  • glycation - process that causes glucose to link to proteins, reducing flexibility
• gene clock hypothesis - people over 100 years of age more likely to have mutated C150T mitochondrial DNA
  • Werner’s syndrome - causes premature aging, found on chromosome 8, affects helicase enzyme in DNA repair
• current aging theories - still no true mechanism for counting
  • connection found between aging, signaling from insulin-like receptors