BSI Lecture 14 Endo/Exocytosis

Question 1

The cell is a dynamic entity that is not only performing specific functions but constantly ______ itself.

Answer 1

renewing

Question 2

What are the pathways that proteins can go after they are synthesized?

Answer 2

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

Question 3

Proteins carry “sorting signal” which are sequence of amino acids that code for their _______.

Answer 3

location

Question 4

Proteins going to the nucleus binds to nuclear ____ _____.

Answer 4

transport receptors

Question 5

Nuclear transport receptor actively transport proteins through the nuclear pores using what energy source?

Answer 5

GTP hydrolysis

Question 6

The nuclear membrane contains large pores to allow access: _____ proteins must be transported in

Answer 6

specific

Question 7

T or F; Small molecules can diffuse in and out freely through nuclear membrane.

Answer 7

true

Question 8

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.

Answer 8

30 - 50

Question 9

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.

Answer 9

GTP

Question 10

Mitochondria are thought to have been “______” sometime during evolution as separate organisms.

Answer 10

acquired

Question 11

Mitochondria have their own DNA and are inherited as complete entities from your ______ in the ovum.

Answer 11

mother

Question 12

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?

Answer 12

false, N-terminus

Question 13

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?

Answer 13

true

Question 14

Mitochondria: Proteins going through the membrane needs to be ______ to pass through specialized sites.

Answer 14

unfolded

Question 15

Proteins that unfold to go through a membrane specialized sites are refolded by ________ proteins.

Answer 15

chaperone

Question 16

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.

Answer 16

endoplasmic reticulum

Question 17

Transmembrane proteins only partially translocate and remain embedded in the ER membrane regardless of final specific membrane destination. T or F?

Answer 17

true

Question 18

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

Answer 18

endoplasmic reticulum

Question 19

Less than 100 Amino Acids is a ______.

Answer 19

peptide

Question 20

Greater than 100 Amino Acids is a _____.

Answer 20

protein

Question 21

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?

Answer 21

false, hydrophobic start sequence

Question 22

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.

Answer 22

retain; don’t retain

Question 23

Can the ER modify proteins?

Answer 23

yes

Question 24

The “faces” of the vesicles are preserved therefore: cytoplasmic vs. extracellular means it is destined for the ____ ______

Answer 24

cell membrane

Question 25

The "faces" of the vesicles are preserved therefore: cytoplasmic vs. "intraorganelle," means it is destine for the ________.

Answer 25

organelle

Question 26

The destination of a vesicle is determined by ______ associated with it

Answer 26

protein

Question 27

How are vesicles formed?

Answer 27

"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.

Question 28

_____ protein uses ____ hydrolysis to form a "neck" around the forming vesicle and helps it pinch off.

Answer 28

Dynamin; GTP

Question 29

The contents of vesicles, (not embedded proteins), are determined by proteins from the _____ family.

Answer 29

adaptin

Question 30

Describe the mechanism of vesicle fusion.

Answer 30

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.

Question 31

Vesicles are then transported to their correct destinations via _____ motors. Does this require ATP?

Answer 31

molecular; yes

Question 32

identification of the correct destination of a vesicle depends on low molecular weight G-proteins of the ____ family

Answer 32

Rab

Question 33

"Tethering proteins" on the target membrane recognizes the ____ on surface of the vesicles.

Answer 33

Rab

Question 34

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.

Answer 34

Rab; v-SNARE; t-SNARE

Question 35

the Golgi Apparatus is composed of groups of _ to ____ flattened and stacked membranous sacks, (cisternae), which vary widely in size and shape.

Answer 35

3;20

Question 36

How are movement between layers of the Golgi apparatus achieved?

Answer 36

by budding and subsequent fusion of vesicles

Question 37

Exocytosis: Constitutive secretions occurs ______ to renew the plasma membrane or for unregulated export.

Answer 37

continuously

Question 38

Exocytosis: Regulated secretions requires a _____.

Answer 38

signal

Question 39

Exocytosis results from the fusion of vesicles released from the cis Golgi Apparatus with the cell membrane. T or F

Answer 39

false, trans

Question 40

Constitutive exocytosis fusion with the cell membrane also releases the contents extracellularly and is therefore responsible for ____ secretion.

Answer 40

unregulated

Question 41

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?

Answer 41

true

Question 42

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?

Answer 42

true

Question 43

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____ .

Answer 43

pinocytosis

Question 44

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 _____.

Answer 44

phagocytosis

Question 45

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.

Answer 45

autophagy

Question 46

The internalized vesicle, (endosome/phagosome/autophagosome), often ends up fusing with a lysosome for_____ ______ prior to recycling.

Answer 46

enzymatic digestion

Question 47

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?

Answer 47

true

Question 48

Phagocytosis is ______ and requires recognition via surface proteins/glycoproteins.

Answer 48

specific

Question 49

Phagocytic cells extend arm-like projections of their cell membranes called _____ which form the intracellular phagosome after internalization.

Answer 49

pseudopods

Question 50

How many RBCs do macrophages ingest a day?

Answer 50

10^11 every day

Question 51

_________, like the constitutive exocytosis pathway, occurs constantly recycling the cell membrane

Answer 51

Pinocytosis

Question 52

Vesicle formation is aided by _____-_____ pits.

Answer 52

clathrin-coated

Question 53

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).

Answer 53

receptor-mediated

Question 54

LDLs are recognized by cell-surface receptors and are internalized via a clathrin-coated vesicle during receptor-mediated exocytosis. T or F?

Answer 54

false, endocytosis

Question 55

Receptor-mediated endocytosis is also used for the uptake of essential metabolites such as vitamin ____ and _____

Answer 55

B12; iron

Question 56

Some pathogens utilize _______-______ endocytosis pathway to gain access to cells such as the influenza viruses and HIV.

Answer 56

receptor-mediated

Question 57

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.

Answer 57

sorting station

Question 58

lysosomes contain many acid _______ (optimized for ↓pH) which degrade substances which are then recycled via transporters.

Answer 58

hydrolases

Question 59

Name the acid hydrolases in the lysosomes.

Answer 59

nucleases, proteases, glycosidases, lipases, phosphatases, sulfatases, phospholipases

Question 60

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).

Answer 60

acid/low

Question 61

_________ can either transfer material to a lysosome or a "late" _______ which may "mature" into a lysosome where full digestion via acid hydrolases occurs.

Answer 61

endosomes; endosome

Question 62

What do chaperones do?

Answer 62

attempt to refold a misfolded protein