Intracellular Transport Flashcards
What is transcytosis?
When molecules from exterior are put inot a vesicle and pass through the cell to the other side without being altered in the cell. Simply passing through.
Describe the many possible fates of proteins once they are translated.
Rough Er –> Cis Golgi –> Anterograde or retrograde transport via vesciles through cisternae of golgi –>
- Secretory vesicle
- Proteasome
- Lysosome
- Plasma membrane
Where are most lipids synthesized / modified?
Smooth ER
What is I-cell disease?
Lysosomal Storage Disease
In normal functioning cells, proteins that are bound for the lysosome to become proteases are tagged with Mannose - 6 - P in the golgi. In disease state, the phosphotransferase enzyme that normally catalyzes this reaction is defective. This leads to the inability of lysosomes to degrade the molecules they are supposed to, so when new material for degradation enters the lysosome it just stays there creating an “inclusion body”. Additionally, the proteins that were supposed to go to the lysosome are released into the cell with no direction, so the cell becomes dysfunctional. Autosomal recessive disease.
What is the purpose of glycosylation of proteins?
Folding, targeting, recognition, immune response
What is clathrin?
Clathrin is a self-polymerizing scaffold protein that is necessary for vesicle formation. It is needed because the cell membrane, although it is fluid, it is still very difficult to break it up into vesicles. Clathrin is a protein that helps make vesicle formation energetically favorable by polymerizing in a way that makes the vesicle formation more energetically favorable.
Describe the process of vesicle formation.
- Clathrin recruited to membrane, cargo recrutied to budding site
- More clathrin molecules recognize bound clathrin and polymerize to form a bud
- This continues until the clathrin pulls the vesicle almost all the way out of the membrane
- Dyanmin binds to neck of budding vescile, hydrolyzes GTP, and constricts to pinch off the vesicle
- Clathrin dissociates once the vesicle is free from the cell membrane
Which type of collagen is most abundant in body?
Type 1
Explain this figure.
A collagen molecule consists of 3 alpha helices coiled with one another (all alpha subunits). This single collagen molecule is called tropocollagen. When many tropocollagens bind together in a repeating pattern with banding, it forms a collegen fibril.
Explain this figure
Explain the Vesicular Model of Intracellular Transport.
Compare this to the Cisternal Maturation Model of Intracellular Transport.
The vesicular model refers to the transfer of contents in the golgi between different cisternae of the golgi via anterograde and retrograde transport of vesicles.
The cisternal maturation model refers to the concept that the cisternae might simply migrate closer to the plasma membrane over time and be replaced by new cisternae when the migrate. This would mean that there would be no vesicle formation except in the trans-golgi network and it would account for the transport of very large proteins, like collagen.
There is evidence to suggest both methods are possible.
Gaucher’s Disease
- What is a telling clinical marker?
- What is the pathohistological hallmark of the disease?
- What is the cause of the disease (basic)?
- Briefly describe what the differences are between Type 1, 2 and 3
- Hepatosplenomegaly
- Lipid-laden macrophages
- Glucocerebrosidase catalyzes breakdown of lipid glucocerebroside (sphigolipid) into a cermamide and glucose. When this enzyme is dysfunctional, this reaction does not happen and there is a build up of lipids in cells that cannot be metabolized or transported.
- Type 1 - adult onset, affects organs and bones but not neurological systems
- Type 2 - juvenile onset, affects neurological systems, children do not live long
- Type 3 - delayed juvenile onset, neurological systems affected but takes longer to develop
Explain this figure.
- In order to import anything into the nucleus, the cargo must be attached to both alpha and beta importin and it must contain the nuclear localization signal.
- Once inside the nucleus, Ran-GTP removes the importin from the cargo and moves it back out to the cytosol by hydrolyzing GTP to GDP, now Ran-GDP.
- In order to export anything out of the nucleus, the cargo must be attached to a nuclear export signal and exportin. Ran-GTP will bind to this complex and facilitate transport outside the nucleus by hydrolyzing GTP –> GDP.
- RanGDP can combine with Exportin to be brought back into the nucleus.
- RanGDP interacts with RanGEF to replenish RanGTP.
Explain this image of RNA Trafficking.
Some mRNAs have signals in 3’UTR that regulate the timing and location of translation. This diagram shows mRNA being shuttled out of the nucleus and then transported to the pre-synapse of the neuron where it is finally translated.
