1/39
Looks like no tags are added yet.
Name | Mastery | Learn | Test | Matching | Spaced |
---|
No study sessions yet.
Exocytosis
The process by which intercellular secretory vesicles release their contents to the outside of the cell (the extra cellular space[ECS])
Endocytosis
The process by which cells internalize contents from the ECS
How does exocytosis releases intracellular molecules to the outside of the cell?
Fusion via the plasma membrane
Macromolecules contained in an intracellular vesicle are released to the extracellular space after the vesicle faces with the plasma membrane.
Animal cells secrete hormones neurotransmitters, mucus, milk proteins, & digestive enzyme.
Plant & fungal cells secrete enzyme and structural proteins for building the cell wall
What is the first type of Exocytosis?
“Trafficking” of a lipid- or protein-bearing intracellular vesicle to the plasma membrane (cell surface)
Active (energy-dependent) process
ATP- & GTP-dependent proteins
What is the second step of Exocytosis?
“Fusion” of vesicular and plasma membranes (share a common lipid bilayer)
What is the third step of Exocytosis?
“Opening/rupture” of the intracellular vesicle & start of membrane integration
What is the fourth step of Exocytosis?
“Release” of macromolecular contents in the EC space & completion of membrane integration
What is the orientation of a vesicular membrane?
The luminal (inner) membrane of the vesicle becomes part of the outer surface of the plasma membrane
Glycolipids & glycoproteins (sugar-containing macromolecules) formed in the ER and Golgi lumens will face the extracellular space
Hydrophilic (water-loving sugars)
What are the mechanisms of exocytosis?
Mechanism(s) of exocytotic vesicle movement to the cell surface are not entirely clear…
But, the cytoskeleton plays an important role by “laying the tracks” for vesicle transport
intracellular “highway systems”
Microtubules use “adaptor proteins” & ATP-dependent ”molecular motors” to bind and move vesicles
Evidence: vesicle movement is blocked when cells are treated with colchicine, a microtubule assembly inhibitor
What are the different types of exocytosis?
All cells need to routinely move material (lipids, proteins) to the PM:
e.g., building/expanding before cell division, adding receptors, replacing the sugar coat of the ECM.
Constitutive exocytosis
“need to survive”
Cells also need to respond to environmental signals in a stimulus & time-dependent fashion
Regulated exocytosis
“need to adapt”
What is the definition of endocytosis?
Pathways bring extracellular or PM-associated materials into the cells
What’s the first step of Endocytosis?
Plasma membrane “invaginates” to capture the to-be transported cellular material
like exocytosis, an active process
direction: EC > cytoplasm
What’s the second step of Endocytosis?
Plasma membrane pinches to enclose the material
What’s the third step of Endocytosis?
Plasma membrane forms a cytoplasmic vesicle
“budding off”
What’s the fourth step of Endocytosis?
The new vesicle “separates” from the plasma membrane as is ready for cystolic use
What type of endocytosis is this?
Phagocytosis
What type of endocytosis is this?
Pinocytosis
What type of endocytosis is this?
Receptor-mediated endocytosis
What is transported during pinocytosis?
Small particulate matter + extracellular fluid (ECF)
Examples of Pinocytosis
Adipose tissue: fat droplet absorption
Intestinal Microvilli: absorb nutrients from the GI tract
Kidney Ducts: formation of urine
Reproductive Eggs: absorb nutrients prior to fertilization
In unicellular organisms (amoeba): water/nutrient uptake
Plasma membrane: Recycling of lipid bilayer components
What molecules are seen in receptor-mediated Endocytosis?
“ligands” (peptides, small molecules, and lipoproteins)
Cell express receptor proteins on the plasma membrane that bind to & concentrate certain molecules needed for/n the cell to function properly.
Concentrate ligands in the cell by a factor of ≥ 1,000-fold
Selectiveness between ligand and receptor
What is the first step in receptor-mediated endocytosis?
Ligand-Receptor binding simulates an intracellular signal to initiate the process of receptor endocytosis.
What is the second step in receptor-mediated endocytosis?
Accumulation of ligand-receptor complexes start to form a “pit” coated with the protein cathrin
Cathrin-coated pit: plasma membrane-ligand-receptor complex
What is the third step in receptor-mediated endocytosis?
Triggers mobilization of cystolic “adaptor” proteins, including dynamin
Further induces Pit curvature > scission
What is the fourth step in receptor-mediated endocytosis?
Pit completely pinches off, creating a coated vesicle
What is the fifth step in receptor-mediated endocytosis?
Cathrin coat is released, leaving an uncoated vesicle
What is the fifth step in receptor-mediated endocytosis?
Coat proteins & dynamin are recycled to the plasma membrane & the uncoated vesicle fuses with an early endosome
process is relatively quick (seconds to minutes)
What is the sixth step in receptor-mediated endocytosis?
Endosome-sequestered receptors are often recycled back to the PM due to the acidified (low pH) early endosome
The pH gradually lowers as the endosome matures, facilitated by an ATP-dependent proton pump
The lower pH dissociates ligand and receptors, allowing receptors to be returned to the membrane
What is the seventh(a) step in receptor-mediated endocytosis?
Some receptor complexes are carried to a lysosome via “late endosomes'“ to be degraded
What is the seventh(b) step in receptor-mediated endocytosis?
Some complexes are recycled back to the plasma membrane to restore receptor activity
What is the seventh(c) step in receptor-mediated endocytosis?
Some complexes can travel via “transport vesicles” to a distinct region of the plasma membrane (often the opposite side of the cell), where they are secreted (transcytosis)
What is the name of the name for vesicles involving protein and lipid transport?
Coated Vesicles
What are the types of coated vesicles?
Clathrin (PM/EE)
COPI (GN><GN, GN>ER)
COPII (ER>GN)
What are the three main function of coated vesicles?
Determine destination
Induce curature needed for vesicle formation
Prevent non-specific fusion with other membranes
What are Caveolin coated vesicles?
Common non-Clathrin-dependent mechanism
Type of a ‘lipid raft’, a PM region rich in cholesterol & sphingolipids
May be involved in cholesterol uptake & maintaining the stability of receptor complexes
What are Clathrin-coated vesicles?
surrounded by coats of two multimeric proteins, clathrin and adaptor protein-2 (AP2).
shape & assembly of clathrin provides induces a flat membrane to form a spherical vesicle
AP binding requires ENERGY (i.e., active/ATP-dependent process)
Exocytosis/Endocytosis are…
active (energy-dependent), eukaryotic cell mechanisms to transport molecules (mainly proteins & lipids) out of (exo-) and into (endo-) cells.
Cells use vesicular transport & the cytoskeleton (esp. microtubules) to accomplish these processes
Exo/endocytosis can occur in an environmental signal-independent (constitutive) & -dependent (regulated) fashion
3 types of endocytosis:
phagocytosis (cellular “eating”), pinocytosis (cellular “drinking”), & receptor-mediated endocytosis (as I personally call it… cellular “sleeping”)
Phagocytosis & pinocytosis can be distinguished based primarily on the size of the material they are internalizing into the cell (phagocytosis involves BIG materials, whereas pinocytosis involves small materials)
Receptor-mediated endocytosis requires…
Clathrin-Coated Pit formation & adaptor proteins (e.g., dynamin, AP) to internalize cell surface receptors
Receptors have 3 main fates: (1) degradation (2) recycling to the cell surface & (3) transcytotic release
Vesicle transport can…
be defined by the Coat Proteins that surround them
Common Coat Proteins are: Clathrin, COPI, COPII, & Caveolin
Coat Proteins determine the vesicle’s (1) destination (2) formation & (3) target specificity