Cytosis Flashcards
What are the requirements for two membranes to fuse?
- They both need to contain SNARE protein.
2. They need to be similar.
What is the function of SNARE proteins?
SNARE proteins recognize, bind to each other and initiate fusion.
What are the two different types of exocytosis?
Constitutive and regulated.
What are the characteristics of constitutive exocytosis?
- Continous
- Slow rate
- The secretory product is not condensed.
- Small vesicles.
What are the characteristics of regulated exocytosis?
- Triggered by a signal from outside the cell –> rise of Ca2+ inside the cell
- A large number of products are released in a short time.
- Secretory product is condensed.
- Large secretory granules (stored until signal)
What are the two types of vesicles cells release to the extracellular space? And what is the difference between the two?
Microvesicles and exosomes.
Microvesicles exit out of the cell by encapsulating a portion of the cell membrane.
Exosomes are large vesicles containing smaller vesicles. the large vesicle fuses with the cell membrane and the small vesicles are released.
What are the three types of endocytosis?
- Phagocytosis
- Pinocytosis
- Receptor-mediated endocytosis.
What is phagocytosis?
- Cell swallowing of large particles.
- Cell surface folds around the particle and creates a large vesicle called phagosomes.
- Energy is required and the cytoskeleton is involved.
What is pinocytosis?
- Cell surface forms an invagination which forms a small vesicle called pinosome.
- Energy is not required and the cytoskeleton is not involved. The liquid is taken up.
What are phagosomes and pinosomes?
Phagosomes are the vesicle resulting from phagocytosis and pinosomes are the vesicles resulting from pinocytosis.
What is receptor-mediated endocytosis?
Pinocytosis of only molecules bound to their specific receptors on the cell membrane.
What kind of proteins are required in receptor-mediated endocytosis?
Coating proteins (clathrin and COP). Help invaginate membrane fractions with receptors. Coated vesicles are formed.
What are the steps of receptor-mediated endocytosis?
- Binding of ligands to cell membrane receptors.
- The receptor molecule moves to the clathrin-coated pit.
- Membrane folds inward.
- Formation of a coated vesicle.
- The vesicle fuses with an endosome.
- Receptors and molecules separate.
- Receptors return to the cell membrane.
- Endosome moves and goes from early endosome to late endosome.
- Late endosome fuses with hydrolase vesicles, where digestive enzymes digest the ligands.
- Late endosome becomes lysosome.
What is the function of lysosomes?
Lysosomes contain hydrolases which perform intracellular digestion.
When do the lysosomal enzymes become active?
Lysosomal enzymes are inactive in the hydrolase vesicles as they are still bound to man-6-P receptors. Once they come in contact with the acidic environment in lysosomes, they become active and disociate from the receptors.
