Cell 3 Flashcards
Macropinocytosis is dependent on which cell cytoskeleton to help with internalizing substances?
actin microfilaments
Which of the five endocytotic pathways require input of energy?
macropinocytosis (ATP-denpendent)
dynamin from clathrin-mediated receptor endocytosis requires input of GTP
Name two types of cells that use macropinocytosis as part of their normal function?
thyroid gland and immune cells
Through what method does Salmonella typhimurium enter cells?
macropinocytosis
How do Cholera and Shiga toxins enter cells?
by hijacking the non-coated vesicular transport mechanism
What are the characteristics of cavelolae mechanism?
invaginations of the membrane have protein Caveolin coats
What virus uses caveolae mechanism to enter cells?
Simian virus 40
What are two types of clathrin-mediated endocytosis?
receptor mediated or non-receptor mediated
Explain the clathrin-mediated receptor endocytosis.
1) lipid rafts in the plasma membrane help attract and aggregate receptor.
2) once the ligand bind on the extracellular side of the receptor, clathrin coats the receptors on the cytosolic side.
3) Dynamin (GTPase) helps “pinch off” the coated vesicle.
4) once the vesicle is internalized, the clathrin coat will dissolve and recycled, the cell then processes the vesicle.
Explain the process in which LDL enters the cell.
1) via clathrin-mediated receptor endocytosis
2) once LDL is bound to the receptor, the receptor on the cytosolic side is associated with a protein called adaptin.
3) adaptin recognizes clathrin and the clathrin-coated pit is formed
4) dynamin pinches off the vesicle and LDL is internalized
If there is a mutation of the coated-pit binding site, what would happen to LDL uptake by the cell?
the binding domain of the receptor will not recognize clathrin and will not be able to coat the pit with clathrin leading to elevated LDL levels in the blood
What can be seen microscopically in an atheroclerotic vessel?
collagen build up, elastin that reveals thinning of the wall, calcification, and neovascularization
What pathway do neurotransmitters enter pre-synaptic cells?
clathrin-mediated endocytosis - no receptors involved
Describe the import of neurotransmitters via clathrin-mediated endocytosis.
This does not require a receptor
1) clarthrin-coated vesicles are filled with neurotransmitters
2) vesicle docks with pre-synaptic cells and release neurotransmitters
3) dynamin pinches off the clathrin-coated vesicle and it travels back to synaptic cleft
What is caveolin-mediated endocytosis?
it is dependent on the protein caveolin coat. Bi-directional
Explain the process of phagocytosis. Are receptors needed?
process in which the cell internalize large substances. it is mediated by receptors
What are three secretion pathways?
exocytosis, porocytosis, exosomes and exosome-like vesicles
What is constitutive pathway of exocytosis?
cell is constantly forming secretory product and secreting them through exocytosis
How do plasma cells secrete antibodies?
via exocytosis
What is the regulative pathway of exocytosis?
secretory product is packaged into secretory vesicles and store in cytoplasm until it is signaled to be released (ex. pancreatic cells)
What is known as quantal release of neurotransmitters?
porocytosis
Describe the porocytosis model
It is a model to describe the release of neurotransmitters. synaptic vesicles bind with the membrane and they partially open to discretely release neurotransmitters. (not in bulk, but quantal)
What are the two types of exocytosis?
constitutive and regulated pathways (cells can have both at the same time)
How do exosomes or exosome-like particles work?
they are formed by the parent cell and released as exosomes by the parent cell
How do reticulocytes utilize exosomes?
reticulocytes are the last stage of erythrocyte formation. this last stage of maturation requires the release of transferrin receptors (which allows the intake of iron for formation of Hb)
How do cytotoxic T cells utilize exosomes?
immune cells release exosomes as signaling cells, which can alter the behavior of T cells
What is different about ribosomes versus other organelles?
ribosomes are non-membranous
Which two subunits make up ribosomes?
60S and 40S
Where are ribosomal subunits assembled?
nucleolus then transported out to cytoplasm
What stain would you use for ribosomes?
Hematoxylin
What must associate with ribosomes otherwise they only exist as subunits?
mRNA
Where are proteins destined to be used by the cell synthesized?
in the cytoplasm by free polyribosomes
Where are proteins destined to be secreted or packaged up into lysosomal compartment synthesized?
rER by attached polyribosomes
What is continuous with the outer membrane of nuclear envelope?
rER
Is rER acidophilic or basophilic?
basophilic
What does translocation mean in the term “co-translational translocation of proteins”?
moving the increasing protein strand into the lumen of the rER
What is co-translational translocation of proteins?
the emerging protein in the ribosome contains a signal peptide that is recognized by the signal recognition particle. the complex is then moved to the surface of rER where it will bind to a docking receptor and a translocon. the protein will continue to be synthesized and it will exit out into the lumen of rER
What is needed in order to transport a newly synthesized protein in the cytoplasm to an organelle within the cell?
a translocon in the receiving organelle along with chaperone proteins
Where are sER enzymes synthesized?
rER
What kind of proteins are shipped out to the Golgi by the ER?
only properly folded proteins
What are the unfolded protein responses?
1) increased synthesis of chaperone proteins
2) reduce protein translation
3) consider apoptosis
What is alpha1-antitrypsin deficiency?
misfolded alpha1-antitrypsin and it polymerizes in the rER
What stain can be used to help detect accumulation of alpha1-antitrypsin?
PAS due to the carbohydrate groups attached to the proteins
What is the function of sER?
steroid synthesis, cholesterol homeostasis, synthesis of phospholipids, glycogen metabolism, detoxification of drugs, and storage, release, uptake calcium ions in striated muscle
Which appears agranular? rER or sER?
sER because they do not contain ribosomes
Will you find proteins associated with both rER and sER? Or just one over the other?
Both, this is why rER and sER are not completely discrete from each other
What is Von Gierke’s disease?
glycogen storage disorder due to mutation in either glucose-6-transporter or glucose-6-phosphatase. will lead to decreased ability to degrade glycogen thus accumulates in the cell
Increase in volume of sER is indicative of what?
- detoxification of phenoarbital, increased number of cytochrome 450 (enzyme required)
- alcohol also has a similar effect thus alcoholics will have increased volume of sER
What is sER associated with muscle called?
sarcoplasmic reticulum
A patient was diagnosed with malignant hyperthermia, it was discovered that he was administered the anesthetic Halothane. What contributed to the spike in temperature?
Patient was overly sensitive to the anesthetic. Halothane promotes excessive leak of calcium ions across the channel and into the sarcoplasm. This caused the muscles to contract. Thus the increased in body temperature was due to increased activity of sarcoplasmic calcium ion pump
