Describe the consequences of increasing Intracellular calcium
1) Excess calcium causes ACTIVATION OF ENZYMES
–> phospholipase degrades phospholipids
–> protease disrupts membranes and cytoskeletal proteins
–> Endonuclease digest DNA (nuclear damage)
–> ATPase breaks down ATP
2) Excess calcium CHANGES PERMEABILITY of mitochondrial membrane
–> membrane potential is altered making it LESS EFFICIENT at producing ATP
Describe the sources of Excess intracellular Calcium
- Endoplasmic reticulum also causes INCREASE in INTRACELLULAR Calcium
- Calcium pump (Ca–>out and Na–>in) on the surface of the membrane breaks down
Describe the consequences of Mitochondrial damage
- Mitochondrial damage caused by INCREASE of Calcium in cytosol, OXIDATIVE STRESS, BREAKDOWN of phospholipids
–> PHOSPHOLIPASE A2 and SPHINGOMYELIN pathways may breakdown lipids
–> lipid breakdown products to free fatty acids and CERAMIDE which may also damage mitochondria
Describe the Hydrogen pump in the mitochondria
- Hydrogen is pumped out of matrix and into intermembrane space to form a potential across inner membrane forms a potential
–> ATP SYNTHASE utilizes the hydrogen potential across inner mitochondrial membrane to turn ADP into ATP
**DESTORYING MEMBRANES IN MITOCONDRIAL ALTERS THIS POTENTIAL AND ATP CAN”T BE FORMED
What are the affects of decrease in oxygen
1) If oxygen supply DECREASES (along with toxins and radiation) causes mitochondrial damage or dysfunction
–> leads to DECREASE IN ATP GENERATION and INCREASE in productiong of Reactive oxygen species leads to cellular abnormalities and NECROSIS
Decrease survival signals by DNA, protein damage
- DECREASE in survival signals by DNA, protein damage
–> INCREASE in Pro-apoptotic proteins (Bax and Bac) form holes within membrane where CYTOCHROME C leaks out and INITIATES APOPTOSIS
–> DECREASE in Anti-apoptotic protines (Bcl-2 and bcl-x) when too much DNA or protein damage causes leakage of mitochondrial proteins and signaling of apoptosis
What are the CAUSES of depletion of ATP
Frequently caused by CHEMICAL INJURY or HYPOXIA
- oxidative phosphorylation cannot proceed because of lack of oxygen or interference with the phosphorylation pathway, the level of ATP in the cell DECREASES
- ISCHEMIA –> decrease in oxidative phosphorylation
What are the effects of depletion of ATP
1) No energy for Na/K pump leads to CELLULAR AND ORGANELLE SWELING (osmotic gradient altered)
2) No energy for Ca++ pump leads to INCREASE INTRACELLULAR Ca++ and ACTIVATION OF ENZYMES (membrane damage)
3) Increase in ANAEROBIC GLYCOLYSIS –> decrease in pH causes Chromatin Clumping (DNA DAMAGE)
4) Detached ribosomes –> monosomes decrease protein synthesis (house keeping protein)
What is the CAUSE of accumulation of oxygen-derived free radicals
- Oxidative stress = accumulation of damage caused by Oxygen-derived free radicals
- Normal metabolism results in formation of radicals
- If cell has MORE DAMAGE than can be PREVENTED or REPAIRED by usual cell mech, then FREE RADICAL DAMAGE can both occur and accumulate in the cell
- Common causes: excess O2, inflammation, reperfusion injury after ischemia, chemical toxicity, radiation, biological agening
What is the major mechanisms of free radical damage in cell
1) Lipid peroxidation of membrane = Peroxides are UNSTABLE and they react with membrane lipids to both DAMAGE them and to FORM MORE peroxides
2) Oxidation of proteins = formation of DISULFIDE BONDS leads to cross-linking leading to INACTIVATION of enzymes or altered function (MISFOLDING OF PROTEINS)
3) DNA damage = free radical interactions with THYMINE causes single-stranded breaks in DNA leading to MUTATIONS implicated in carcinogenesis
Describe Peroxides
- Peroxides are formed from double bonds of unsaturated fatty acids that are attached by OXYGEN-DERIVED free radicals
- peroxides are unstable and react with membrane lipids to both damage them and to form MORE PEROXIDES
–> peroxidation of membranes is self-sustaining and can cause a lot of damage unless radicals are captured by free radical scavengers such as VITAMIN E embedded in membranes
- Vitamin C, A and beta-carotene are ANTIOXIDANTS
What are causes of membrane damage?
1) Reactive oxygen species cause LIPID PEROXIDATION –> phospholipid loss and membrane damage
2) Decrease in O2 –> decrease in ATP –> decrease phospholipid reacylation/synthesis causing phospholipid loss and membrane damage
3) Increase in cytoslic Ca++ causes PHOSPHOLIPASE activation –> INCREASES phospholipid degradation and lipid breakdown products –> membrane damage
4) Increase in cytosolic Ca++ causes PROTEASE ACTIVATION –> cytoskeletal damage–> membrane damage
