Lysosomes

• single membrane bound organelles • contain ~ 60 different enzymes • acidic pH of 5 • size ranges from 0.1 micrometers to 1.2 micrometers

~300

Lysosomes act as the digestive system of a cell and digest intracellular proteins and carbohydrates but also molecules and pathogens from outside the cell

They bud off of the trans face of the Golgi apparatus

Because the glycosilation protects the proteins from the proteases present in the lumen

• Endocytosis • Phagocytosis • Pinocytosis • Autophagy

The digestion of material of extracellular origin

The digestion of material of intracellular origin

V-ATPase pumps protons from the cytoplasm to the lysosomal lumen which maintains the acidic environment within the lysosome

It targets proteins to lysosomes It allows lysosomal hydrolases and membrane proteins to be delivered to lysosomes

They are inherited metabolic diseases characterised by abnormal build up of materials in cells as a result of enzyme deficiencies

• Hunter & Hurler syndrome • Tay-Sachs disease • Gaucher disease • Inclusion cell disease

It develops as a result of large sugar molecules building up in body tissues Symptoms include an enlarged head, thickening of the lips and a distended abdomen due to enlarged internal organs

Develops as a result of deficiency of the hexosaminidase enzyme which means lipids accumulate in the brain and other organs Symptoms include mental challenges, blindness and death within 3 years

Develops due to the accumulation of glycolipids Symptoms include enlargement of the liver and spleen, anaemia and lung disease

Caused by deficiency of N-glucosamine phosphotransferase which is what transfers M6P Symptoms include psychomotor challenges and death

The endosomal-lysosomal system is made up of a set of intracellular membranous compartments which interconvert It is comprised of early endosomes, recycling endosomes, late endosomes and lysosomes

• for traffic and digestion of endocytosed molecules • for sorting and recycling cellular components • for autophagy

Membrane bound vesicles formed by endocytosis and found in every animal cell

1) Endocytosed molecules are delivered in vesicles to small, irregularly shaped intracellular organelles called early endosomes 2) Some of these molecules are recycled to the plasma membrane whilst some pass into late endosomes 3) They are then passed to lysosomes where they are degraded

1) Phagocytes engulf objects to form a phagosome 2) The phagosome fuses with a lysosome to form a phagolysosome 3) The hydrolysed products enter the cytosol

Pinocytosis is the intake of liquid particles to form vesicles known as pinosomes It balances exocytosis because the cell surface area and volume remain constant by recycling cell membrane parts to maintain the size of the cell

• the target organelle or protein is wrapped in a double membrane from the ER which produces an auto-phagosome • the autophagosome fuses with a lysosome to produce a autophagolysosome • indigestible remnants are retained as granules that accumulate with age in residual bodies • debris is released from the cell surface via exocytosis