what is a lysosome?
an organelle of the endomembrane system that contains digestive enzymes capable of degrading all of the major classes of biological macromolecules
What does a lysosome look like?
single membrane - the lumenal side of membrane proteins is highly glycosylated which protects membrane proteins from lysosomal proteases
What type of environment is inside the lysosome - in terms of pH?
Acidic environment of 4.0-5.0
This favors enzymatic digestion of macromolecules both by activating acid hydrolases and by partially denaturing the macromolecules targeted for degradation
What types of acid hydrolases lie within the lysosome?
5 phosphatases, 14 proteases and peptidases, 2 nucleases, 6 lipases, 13 glycosidases and 7 sulfatases
Where do lysosomal enzymes come from?
synthesized by ribosomes, go from ER to Golgi for processing and packaging, from there they are endosomes and mature into lysosomes by the activation of acid hydrolases
what are heterophagic lysosomes?
lysosomes containing substances of extracellular origin (come from outside the cell)
What are autophagic lysosomes
lysosomes that contain materials of intracellular origin (from inside the cell)
How do the digested pieces of nucleic acids, proteins, carbohydrates etc, get across the membrane and into the cytosol?
some cross by faciliated diffusion while others need active transport to cross into the cytosol
the acidity of lysosomal lumen contributes to an electochemical proton gradient across the lysosomal membrane
what is a residual body?
indigestable material in the lysosome that remains as digestion ceases
What is autophagy?
the digestion of old or unwanted organelles or other cell structures
what is macrophagy?
a type of autophagy that begins when an organelle or other structure becomes wrapped in a double membrane derived from the ER
what is an autophagic vesicle?
a vesicle that resulted from macrophagy
What happens when there are lysosomal storage diseases?
skeletal deformaties, muscle weakness and mental retardation
Hurler syndrome and Hunter syndrome - both arise from defects in the degradation of glycosaminoglycans