Lysosomes
● Proteins that operate in the lysosomes, are made at the ER, then transported to the cis side of the Golgi
apparatus. Then go on to the lysosomes for secretions via the trans side.
● Sometimes, there are vesicles inside the larger
lysosome.
● Single membrane.
● Look very different from each other as they have
different content. They have heterogeneous content[ the
content in the lysosome actually varies in the different
lysosomes].
● The pH is very acidic because of the enzymes
[highlighted in red] that require acidic pH’s for work.
● The membrane has a lot of transmembrane proteins
inserted into it which are heavily glycosylated on the lumen
side of the lysosome. Glycosylation; is a form of
co-translational and post-translational modification.
● Have thick sugar polysaccharides that protect the lysosome from degrading itself.
Substrate delivery to lysosomes
Lysosomes digest and hydrolyse substances that aren’t needed anymore, and these substances can be
extracellular or intracellular.
● Extracellular substrates: Endocytosis
○ Fluid-phase endocytosis of molecules and lipoproteins (includes receptor-mediated endocytosis).
Lipoproteins; group of soluble proteins made from lipids & fats that combine with & transport fat
or other lipids in the blood plasma.
○ Phagocytosis “cell eating” of particles ≥ 0.5 µm
● Intracellular substrates
○ Microautophagy membrane of the lysosome invaginates. ‘Deformation inwards’ (invagination of
the lysosomal membrane)
○ Macroautophagy chunks/ or entire organelles that enter the ER and fuse to the lysosome, where
they are degraded. (Cytosol or organelles wrapped in ER membrane, which then fuses with
lysosomes)
○ Selective transport of proteins across the lysosomal
membrane
● Endocytosis; the plasma membrane forms a little pit. The early
endosome forms the late endosome when they mature as the pH
drops little by little. Then, the late endosomes form the lysosome.
● Proteins that operate in the lysosomes, are made at the ER, then transported to the cis side of the Golgi
apparatus. Then go on to the lysosomes for secretions via the trans side.
● Sometimes, there are vesicles inside the larger
lysosome.
● Single membrane.
● Look very different from each other as they have
different content. They have heterogeneous content[ the
content in the lysosome actually varies in the different
lysosomes].
● The pH is very acidic because of the enzymes
[highlighted in red] that require acidic pH’s for work.
● The membrane has a lot of transmembrane proteins
inserted into it which are heavily glycosylated on the lumen
side of the lysosome. Glycosylation; is a form of
co-translational and post-translational modification.
● Have thick sugar polysaccharides that protect the lysosome from degrading itself.
Substrate delivery to lysosomes
Lysosomes digest and hydrolyse substances that aren’t needed anymore, and these substances can be
extracellular or intracellular.
● Extracellular substrates: Endocytosis
○ Fluid-phase endocytosis of molecules and lipoproteins (includes receptor-mediated endocytosis).
Lipoproteins; group of soluble proteins made from lipids & fats that combine with & transport fat
or other lipids in the blood plasma.
○ Phagocytosis “cell eating” of particles ≥ 0.5 µm
● Intracellular substrates
○ Microautophagy membrane of the lysosome invaginates. ‘Deformation inwards’ (invagination of
the lysosomal membrane)
○ Macroautophagy chunks/ or entire organelles that enter the ER and fuse to the lysosome, where
they are degraded. (Cytosol or organelles wrapped in ER membrane, which then fuses with
lysosomes)
○ Selective transport of proteins across the lysosomal
membrane
● Endocytosis; the plasma membrane forms a little pit. The early
endosome forms the late endosome when they mature as the pH
drops little by little. Then, the late endosomes form the lysosome.
