Lysosomes, Vacuoles

lysosomes

membrane sacs filled with hydrolytic enzymes that breakdown macro molecules

lysosomes function

phagocytosis (engulfing food particles)

autophagy (recycling old cell parts)

lysosome enzymes

work best in acidic pH

made in rough ER, processed in golgi, some lysosomes bud from the golgi

how do lysosomes not self digest?

pH control - lysosomal enzymes (acid hydrolases) only work in acidic conditions so if a lysosome breaks, the enzymes become inactive

structural protection - lysosomal membrane highly glycosylated, so they’re resistant to digestion

phagocytosis

some cells eg macrophages engulf harmful microbes and destroy them in lysosomes

autophagy

damaged organelles are wrapped in a double membrane autophagosome, which fuses with a lysosome to digest and recycle the contents

nonselective autophagy

regulated by nutrient availabilitys

selective autophagy

mediated by receptors that recruit cargo to the autohphagosome membrane

mitophagy

selectively degrades mitochondria

lysosomal storage diseases

gene for one of the hydrolytic enzymes of the lysosome may not be functional

causes accumulation of the component that can’t be digested

tay-sachs disease

a lipase is missing

leads to accumulation of lipids in the brain

inclusion cell disease

almost all lysosomal enzymes missing due to being mistakenly secreted instead of delivered to lysosomes

leads to inclusions of undigested substrates in the cell, causing multi-organ disfunctions

vacuole

large vesicles derived from the ER and golgi

food vacuoles (animal cells)

formed by pahgocytosis

contractile vacuoles (protists)

pump excess water out to prevent bursting

central vacuoles (plants)

store ions, nutrients, water

contain sap (repository of inorganic ions)

sap plays major role in growth of plant cells and maintains turgor

digestive vacuoles (plants)

function as plant lysosomes

storage vacuoles (plants)

for storing reserves

how do plant cells grow using vacuoles

storing more water in the vacuole instead of making more cytoplasm

the cytosol is pushed to the edges of the cell, supported by actin filaments

peroxisomes

single membrane compartments that break down molecules using oxidation reactions

peroxisomes function

fatty acid breakdown for fuel for respiration

detoxification of alcohol and other harmful compounds in the liver

hydrogen peroxide breakdown to water using catalase

gloxysomes

in fat storing tissues of plant seeds

convert fatty acids to sugar to feed the emerging seedling

why is hydrogen peroxide dangerous

peroxisomes produce H2O2 as byproduct of metabolism

H2O2 is toxic so catalse converts it to harmless water and oxygen

X-linked adrenoleukodystrophy (ALD)

defective peroxisomal enzyme = unable to break down very long chain fatty acids

fatty acids accumulate, damaging the myelin sheath in the nervous system. nerves cannot conduct impulses properly

leads to neurological symptoms and paralysis

treatment of ALD

Lorenzo’s Oil (mix of rapeseed and olive oil)

reduces the buildup of very long chain fatty acids

works best before symptoms appear