Chapter 12 endocytosis
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60 Terms
What is endocytosis?
The process by which eukaryotic cells continually take up fluid and large/small molecules by membrane invagination forming vesicles.
What happens to most endocytic vesicles?
They fuse with lysosomes.
What are the three main types of endocytosis?
Phagocytosis, pinocytosis, and receptor-mediated endocytosis.
What does phagocytosis internalize?
Bacteria and large particles.
Which cells perform phagocytosis?
Macrophages and neutrophils.
What does pinocytosis internalize?
Fluids.
What is receptor-mediated endocytosis?
A selective uptake process using receptors.
What are endosomes?
Membrane-bound compartments that receive endocytic vesicles and sort cargo.
What is recycling in endocytosis?
The return of receptors or membrane components back to the plasma membrane.
What can specialized phagocytic cells ingest?
Bacteria and dead cells
What structures extend to engulf particles in phagocytosis?
Pseudopods.
What is formed after engulfment during phagocytosis?
A phagosome.
What does pinocytosis internalize?
Fluids and plasma membrane.
What is micropinocytosis vesicle size?
0.2 μm
Is micropinocytosis clathrin dependent?
Mostly yes.
What is macropinocytosis vesicle size?
0.2–10 μm.
Is macropinocytosis clathrin dependent?
No (clathrin independent).
Does macropinocytosis internalize plasma membrane?
Yes.
Why is receptor-mediated endocytosis specific?
It requires ligand binding to a specific receptor.
How is cholesterol transported in blood?
Bound to low-density lipoproteins (LDL).
Why is cholesterol transported in LDL?
Because cholesterol is extremely insoluble in water.
What happens to LDL in acidic endosomes?
LDL is released from its receptor.
What regulates receptor amount on the surface?
Endocytosis helps regulate receptor levels.
What protein transports iron (Fe) in blood?
Transferrin.
When does transferrin bind Fe?
At neutral pH.
When does transferrin bind transferrin receptor (TfR)?
At neutral pH when loaded with Fe.
What happens to endosomes over time?
They undergo maturation.
Can viruses enter via receptor-mediated endocytosis?
Yes.
Example of virus entering via endocytosis?
HIV.
What is the host cell trying to do during viral entry?
Recognize and destroy the virus.
What is the virus trying to do?
Use host machinery to replicate.
Do all viruses enter through endocytosis?
No.
What is the structure of the endosomal compartment?
A complex set of connected membrane tubes and larger vesicles.
What are the three fates of endocytosed material?
Recycling, degradation, transcytosis.
What maintains lysosomal acidity?
H+ pump.
What does acidic pH do in endosomes?
Releases cargo from receptors.
What does acidic pH do in lysosomes?
Activates proteolytic enzymes (digestive enzymes)
What are lysosomes?
Principal sites of intracellular digestion.
How many types of hydrolytic enzymes are in lysosomes?
About 40 types.
What do lysosomal enzymes degrade?
Proteins, nucleic acids, oligosaccharides, lipids.
Optimal pH of lysosomal enzymes?
5
cytosolic pH
7.2
Name lysosomal enzyme types.
Nucleases, proteases, glycosidases, lipases, phosphatases, sulfatases, phospholipases.
What transports digested products to cytosol?
Lysosomal transporters.
What tag targets digestive enzymes to lysosome?
Mannose-6-phosphate.
Where is mannose-6-phosphate added?
ER and Golgi.
What is autophagy?
Recycling pathway for cellular components.
What organelles can be degraded via autophagy?
Lysosomes, mitochondria.
What structure forms in autophagy?
Double membrane autophagosome.
Why is autophagy important?
Removes damaged organelles and provides energy during starvation.
What are other pathways to lysosome?
Endocytosis and phagocytosis.
First method to study vesicular transport?
In a test tube (in vitro).
What can be isolated in vitro?
Vesicles and their target membranes.
Example of purified vesicle type?
COPI vesicles.
Second method?
Model organisms (yeast).
Why use yeast?
Identify proteins required for vesicle formation, targeting, and fusion.
Third method of study?
Live cell imaging.
Is ER localized in one region?
No, it fills empty space throughout the cell.
What cytoskeletal structures transport vesicles?
Microtubules.
Why are microtubule ends important?
They are oriented to direct transport directionally.