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Unformatted text preview: its (fingers
& toes) during development.
toes) Elimination of excess neurons in developing
nervous system (up to 50% of the total of
developing embryonic neurons).
developing Important in maintenance of adult tissues! Balancing cell proliferation & maintaining constant
cell numbers in tissues that turnover regularly.
cell Example 500 billion blood cells die daily - balancing their
continual production in the bone marrow.
continual Defense mechanism against damaged or infected cells. Example Virus-infected cells frequently undergo
apoptosis, thereby preventing virus spreading. Example DNA damage often induces a cell into apoptosis
thus eliminating dangerous mutations that may
lead to cancer.
lead Apoptosis OVERVIEW
Apoptosis Caspases & Apoptosis
Caspases The EXECUTIONERS
of programmed cell death!
(“C” + “Asp” + ase) Protease enzymes with Cysteine residues at their
active Cleave substrate proteins after Aspartic acid (Asp)
residues. Cleave ~100 different cell target proteins!! Caspase Example
Caspase Cell Death Receptors
Cell Cell death signals Polypeptides belonging to the tumor necrosis factor
(TNF) Cell death receptors TNF Receptor Family Virus infected cells, Cancerous cells, other Immune cells Ligand binding results in receptor trimerization, association
with “adaptor” proteins and Caspase-8, autocleavage or
activation of Caspase-8, activation of more caspases and other
“enhancing” Signaling Cell Survival
Signaling Default Status of Most Cells Apoptosis unless
actively suppressed by “survival signals.”
.” There are many pathways that signal cell
survival and inhibition of apoptosis!
survival Example Example Neurons that make the correct
“connections” don’t die. They
are maintained by nerve growth
factors from the tissues.
factors Apoptosis Summary
Apoptosis Programmed cell death is “normal” and
essential to balance in multicellular life
forms like us!
forms Caspases are a family of enzymes that cause
apoptosis Cells can be signaled to undergo apoptosis
Cells Apoptosis can be avoided by survival signals Questions?
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