BSI Lecture 14 Endo/Exocytosis Flashcards
The cell is a dynamic entity that is not only performing specific functions but constantly ______ itself.
renewing
What are the pathways that proteins can go after they are synthesized?
1) It can be taken into the nucleus via pores
2) It can travel and become a part of the rough ER membrane
3) It can travel to the golgi apparatus and be packaged for intracellular transport or be exported out of the cell
Proteins carry “sorting signal” which are sequence of amino acids that code for their _______.
location
Proteins going to the nucleus binds to nuclear ____ _____.
transport receptors
Nuclear transport receptor actively transport proteins through the nuclear pores using what energy source?
GTP hydrolysis
The nuclear membrane contains large pores to allow access: _____ proteins must be transported in
specific
T or F; Small molecules can diffuse in and out freely through nuclear membrane.
true
Large molecules must be specifically transported through a disordered “tangle” of fibers that act as a filter to get into the nucleus, these pores are complex structures composed of more than ____ different proteins.
30 - 50
Proteins carrying nuclear localization signals, are recognized by a nuclear transport receptor, then binds to nuclear pore fibrils and transports the complex through the pore into the nucleus. The hydrolysis of _____, provides the energy for this transport which can be very rapid.
GTP
Mitochondria are thought to have been “______” sometime during evolution as separate organisms.
acquired
Mitochondria have their own DNA and are inherited as complete entities from your ______ in the ovum.
mother
Proteins targeted for mitochondria have a specific C-terminal sequence which allows their recognition and subsequent translocation through the mitochondrial membranes at specialized sites where the 2 membranes touch. T or F?
false, N-terminus
Mitochondria: The targeting sequence of the protein is removed, which sometimes reveals a new “sorting code” that further specifies their final location. T or F?
true
Mitochondria: Proteins going through the membrane needs to be ______ to pass through specialized sites.
unfolded
Proteins that unfold to go through a membrane specialized sites are refolded by ________ proteins.
chaperone
The ____ is the most extensive membranous organelle which not only requires many proteins for its own function but produces and packages membranes and macromolecules for use in other organelles, (Golgi Apparatus, endosomes, lysosomes, cell membrane), and cellular export.
endoplasmic reticulum
Transmembrane proteins only partially translocate and remain embedded in the ER membrane regardless of final specific membrane destination. T or F?
true
Protein synthesis often starts in the cytoplasm on “free” ribosomes, (rRNA), but a signal sequence is recognized by the signal recognition particle, (SRP), which directs the ribosome to the ____ membrane
endoplasmic reticulum
Less than 100 Amino Acids is a ______.
peptide
Greater than 100 Amino Acids is a _____.
protein
Proteins with a TMD, a “hydrophilic start” sequence, (followed by an appropriate “stop” sequence), allows the partially translocated peptide/protein to form an appropriate hydrophobic alpha-helix within the membrane and be retained: only one TMD is formed as the “start” sequence is now removed. T or F?
false, hydrophobic start sequence
Translocation mechanism for a protein destined to remain incorporated into a membrane with 2 TMD’s differs with one with only 1 TMD is due to the specific amino acid signaling sequences that _____ or _____ _____ the “start” sequence.
retain; don’t retain
Can the ER modify proteins?
yes
The “faces” of the vesicles are preserved therefore: cytoplasmic vs. extracellular means it is destined for the ____ ______
cell membrane
The “faces” of the vesicles are preserved therefore: cytoplasmic vs. “intraorganelle,” means it is destine for the ________.
organelle
The destination of a vesicle is determined by ______ associated with it
protein
How are vesicles formed?
“Cargo molecules” (proteins to be transported) are recognized by receptors which, via adaptin, organize clathrin molecules to form a supporting “cage” helping form the vesicle. After dynamin pinches off the vesicle the clathrin is removed and recycled leaving the naked vesicle.
_____ protein uses ____ hydrolysis to form a “neck” around the forming vesicle and helps it pinch off.
Dynamin; GTP
The contents of vesicles, (not embedded proteins), are determined by proteins from the _____ family.
adaptin
Describe the mechanism of vesicle fusion.
a tethering protein on the cell membrane grabs the rab protein in the vesicle. It pulls it down and the t-SNARE on the cell membrane attaches to the v-SNARE on the vesicle. This causes fusion into the cell.
Vesicles are then transported to their correct destinations via _____ motors. Does this require ATP?
molecular; yes
identification of the correct destination of a vesicle depends on low molecular weight G-proteins of the ____ family
Rab
“Tethering proteins” on the target membrane recognizes the ____ on surface of the vesicles.
Rab
Vesicles: Additional recognition is via the _____ proteins: ____ on vesicles bind to complementary______ on target membranes and draw them closely together, excluding water, to promote fusion.
Rab; v-SNARE; t-SNARE
the Golgi Apparatus is composed of groups of _ to ____ flattened and stacked membranous sacks, (cisternae), which vary widely in size and shape.
3;20
How are movement between layers of the Golgi apparatus achieved?
by budding and subsequent fusion of vesicles
Exocytosis: Constitutive secretions occurs ______ to renew the plasma membrane or for unregulated export.
continuously
Exocytosis: Regulated secretions requires a _____.
signal
Exocytosis results from the fusion of vesicles released from the cis Golgi Apparatus with the cell membrane. T or F
false, trans
Constitutive exocytosis fusion with the cell membrane also releases the contents extracellularly and is therefore responsible for ____ secretion.
unregulated
In addition there exists a regulated exocytosis pathway found only in cells with specialized secretory functions such as endocrine cells: vesicles accumulate near the cell membrane awaiting the appropriate signal for release, (often an increase in intracellular calcium: ↑[Ca2+]i). T or F?
true
The constant addition of new cell membrane is typically matched by a constant recycling of the cell membrane which maintains the size of the cell/surface area of the membrane. T or F?
true
Endocytosis is the reverse of exocytosis: the cell membrane invaginates to form a new inward, budding vesicle in order to import substances and associated fluid; this is specifically____ .
pinocytosis
Some specialized cells can ingest old cells, (for recycling), malfunctioning cells, (cancerous), and even invading pathogens such as bacteria, (macrophages and neutrophils: see Immunology): this is _____.
phagocytosis
Just as the plasma membrane is constantly renewed, so are all the intracellular organelles by a process known as ____: if this process is disrupted it can be fatal.
autophagy
The internalized vesicle, (endosome/phagosome/autophagosome), often ends up fusing with a lysosome for_____ ______ prior to recycling.
enzymatic digestion
Pinocytic vesicles are normally <150 nm in diameter whereas a phagocytic vesicle, known as a phagosome, is typically >250 nm in diameter. T or F?
true
Phagocytosis is ______ and requires recognition via surface proteins/glycoproteins.
specific
Phagocytic cells extend arm-like projections of their cell membranes called _____ which form the intracellular phagosome after internalization.
pseudopods
How many RBCs do macrophages ingest a day?
10^11 every day
_________, like the constitutive exocytosis pathway, occurs constantly recycling the cell membrane
Pinocytosis
Vesicle formation is aided by _____-_____ pits.
clathrin-coated
A specific endocytosis pathway known as _____-_____ endocytosis requires recognition by specific cell surface receptors: this is an efficient system for concentrating a substance within a cell, (x1000 compared to constitutive pinocytosis).
receptor-mediated
LDLs are recognized by cell-surface receptors and are internalized via a clathrin-coated vesicle during receptor-mediated exocytosis. T or F?
false, endocytosis
Receptor-mediated endocytosis is also used for the uptake of essential metabolites such as vitamin ____ and _____
B12; iron
Some pathogens utilize _______-______ endocytosis pathway to gain access to cells such as the influenza viruses and HIV.
receptor-mediated
Endosomes are another organelle system composed of membranous tubules and large vesicles, (the “import” equivalent of the ER and Golgi?), which functions as a “_____ _____” for endocytotic vesicles.
sorting station
lysosomes contain many acid _______ (optimized for ↓pH) which degrade substances which are then recycled via transporters.
hydrolases
Name the acid hydrolases in the lysosomes.
nucleases, proteases, glycosidases, lipases, phosphatases, sulfatases, phospholipases
Endosomes maintain an ____/____pH which can cause the dissociation of some receptors but some are retained and later degraded in lysosomes while others continue to travel with their “cargo” to a different region of the cell membrane, (transcytosis).
acid/low
_________ can either transfer material to a lysosome or a “late” _______ which may “mature” into a lysosome where full digestion via acid hydrolases occurs.
endosomes; endosome
What do chaperones do?
attempt to refold a misfolded protein
