Endocytosis
Large particles cannot cross the cell membrane → they enter the cell by endocytosis.
Types of endocytosis:
Pinocytosis
Phagocytosis
Pinocytosis
Means drinking by the cell.
for intake of macromolecules.
Occur continuously in most cells.
Cell expresses receptors on cell membrane for molecules that it wants to take in
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These receptors are located on coated pits
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The molecule binds the receptors
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Proteins underneath the pit pull the membrane inside the cell & ...
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break the mouth of the pit
↓ Formation of vesicle inside the cell containing the molecule and extracellular fluid
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Vesicle formed by pinocytosis is called pinocytotic vesicle. These vesicles are very small.
This process required energy from ATPs.
Phagocytosis
Means eating by cell.
for intake of larger particles like bacteria, whole cell etc.
Only some cells have capacity for phagocytosis e.g. tissue macrophage.
Mechanism of phagocytosis is similar to pinocytosis.
Som ligand on the particle to be ingested binds with the cell surface receptor
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Membrane around this attachment evaginates to cover the particle
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the membrane merges on the other side
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forms vesicle inside the cell
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Vesicle formed by phagocytosis is called phagocytic vesicle. It's large.
Digestion of Ingested Material
The vesicle formed by pinocytosis/phagocytosis merges with lysosome
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Lysosome empties its hydrolase enzymes in the vesicle
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Now the vesicle is called digestive vesicle
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Hydrolase enzymes break down the ingested particles
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1. Smaller molecules like amino acid, glucose, etc → cross the membrane of vesicle → enter the cytoplasm.
2. Indigestible material is left inside the vesicle → excreted out of the cell by exocytosis.