Intracellular Compartments

Question 1

What is the proposed origin of the mitochondria

Answer 1

An aerobic bacteria fused with a cell, its plasma membrane degraded inside the cell, and resulted in two separate mitochondria within the cell

Question 2

What is protein sorting

Answer 2

Transfer of proteins into compartments where they are needed

Question 3

Where does protein sorting occur

Answer 3

In the cytosol, on free ribosomes

Question 4

Does protein transport require energy

Answer 4

Yes

Question 5

What is a signal sequence

Answer 5

A specific chain of amino acids that directs proteins to specific organelles

Question 6

When are signal sequences removed

Answer 6

After sorting

Question 7

What is the double membrane of the nucleus called

Answer 7

The nuclear envelope

Question 8

What is the space in between the outer and inner nuclear membranes called

Answer 8

Perinuclear space

Question 9

What is the nuclear pore complex

Answer 9

Nuclear pores contain cytosolic fibrils, nuclear basket, and pore-complex proteins - they provide access to the nucleus and regulate the transfer of proteins and RNA across the nuclear envelope

Question 10

Is the flow in nuclear pores selective

Answer 10

Yes

Question 11

What identifies the proteins that are required to be imported

Answer 11

They have a nuclear localization sequence

Question 12

What moves OUT of the nucleus

Answer 12

Matured processed RNA, and ribosomal RNA

Question 13

What moves INTO the nucleus

Answer 13

Histones, proteins required for DNA transcription and replication, and dNTPs/rNTPs

Question 14

What are the three ways to import proteins to organelles

Answer 14

• Nuclear transport
• Transport across membranes
• Transport by vesicles

Question 15

Similarities of mitochondria and chloroplasts in plants in relation to protein transport

Answer 15

Each has double membranes (chloroplasts have a third membrane called thylakoids), most of their proteins are encoded by nuclear genome, so those proteins must be transported

Question 16

Transport of proteins in mitochondria and chloroplasts

Answer 16

Proteins are made by free ribosomes in the cytoplasm (signal sequence at N terminus, proteins must move across both outer and inner membranes at special sites where layers are in contact), proteins must unfold to be imported and refold once signal sequence is removed

Question 17

Subsequent transport within the mitochondria requires what extra sequence

Answer 17

Another signal sequence, revealed after first one is removed

Question 18

Vesicular transport

Answer 18

ER most extensive of the endomembrane system, serves as an entry point for proteins in itself as well as proteins for the Golgi body, lysosomes, endosomes, etc., and once in the ER proteins will never re-enter the cytosol

Question 19

What is protein translocation

Answer 19

For example, when the signal sequence is being formed on mRNA, the SRP binds to it and brings it to the SRP receptor in the membrane (like a binding site), which leaves the signal sequence at the translocation channel to be transported across the membrane

Question 20

What two types of protein are transported to the ER

Answer 20

• Water soluble proteins (destined for lumen)
• Prospective transmembrane proteins (destined for plasma membrane of ER or another cell)

Question 21

Which proteins cross all the way over membranes

Answer 21

Soluble proteins

Question 22

What are single-pass transmembrane proteins

Answer 22

The signal sequence binds to the peptidase and draws it through the translocation channel until the stop sequence is read at some distance on the protein, where it then stops feeding - part of the protein moves over the membrane but some does not due to the stop signal

Question 23

Temporary vesicles

Answer 23

• allow material to enter and leave cells
• move material between endomembrane compartments
• carry soluble proteins (in the lumen) to the plasma membrane for secretion
• move membrane proteins to be expressed on the cell surface

Question 24

What is vesicle budding driven by

Answer 24

Formation of protein coat

Question 25

What does vesicle docking depend on

Answer 25

Tethers and SNAREs

Question 26

How does docking of a vesicle work

Answer 26

Once budded, they must find their proper destination, where it recognizes and docks - each displays molecular markers that must be recognized by complementary receptors on target membrane

Question 27

What are RAB proteins

Answer 27

Family of monomeric GTPases displayed on vesicle surface

Question 28

Where are tethering proteins

Answer 28

Displayed on cytosolic side of target membrane

Question 29

SNAREs

Answer 29

Transmembrane protein on vesicle (v-snare) and transmembrane protein on target (t-snare) that consolidate docking and catalyze membrane fusion

Question 30

Docking, Fusion and Tethering are three steps done in what specific order

Answer 30

1. Tethering 2. Docking 3. Fusion

Question 31

ER processing steps along secretory pathway

Answer 31

- Most proteins are covalently modified in the ER, which leads to the formation of disulphide bonds and stabilizes protein shape - Addition of sugar groups (glycosylation) which have various functions depending on the sugar - protects protein from degradation, helps direct protein to proper organelle, and if displayed on the surface it allows for cell-cell recognition

Question 32

What is an interchain disulfide bond

Answer 32

Disulfide bonds between different proteins

Question 33

What is an intrachain disulfide bone

Answer 33

Disulfide bonds within a folded protein

Question 34

What is the function of oligosaccharide transferase protein

Answer 34

The oligosaccharide enter the ER, the N-acetylglucosamine group disattaches from the phosphate group and attaches to the amine group of asparagine side chains

Question 35

Only properly ______ proteins can enter the ER

Answer 35

Folded

Question 36

What is the unfolded protein response (UPR)

Answer 36

If protein production exceeds the amount able to be folded, the result is misfolded proteins accumulate - this signal increases the expression of chaperone proteins and other proteins that assist in folding; which expands the ER - If the cell cannot keep up, the UPR triggers cell death: apoptosis

Question 37

What is apoptosis

Answer 37

The death of cells which occurs as a normal part of cell growth and development

Question 38

How can the Golgi body be described in physical make up

Answer 38

Flattened sacs called cisternae that are organized into compartments

Question 39

What is the cis network of the ER

Answer 39

Newly formed, the "entry" part near the ER

Question 40

What is the trans network of the ER

Answer 40

Breaking away, the "exit" part away from the ER

Question 41

What are the functions of Golgi apparatus

Answer 41

Modify proteins coming from the ER: - peptides shortened by proteases - amino acids modified - CHO groups added in ER are modified or removed - glycosylation Most complex proteins are synthesized in the Golgi - glycos amino glycans in the extracellular matrix in animals - pectins, hemicellulose in plants

Question 42

What are proteases

Answer 42

Enzymes that break down proteins

Question 43

What is constituted secretion

Answer 43

Proteins are secreted from the cell at a constant rate, no matter the outer environment

Question 44

What is regulated secretion

Answer 44

Proteins secreted from cell in large amounts when a signal is read from the outer environment

Question 45

What are the two main endocytic pathways

Answer 45

Pinocytosis (cell drinking) and phagocytosis (cell eating)

Question 46

What is pinocytosis

Answer 46

"Cell drinking": tiny vesicles are formed called endosomes - done in all eukaryotic cells

Question 47

What is phagocytosis

Answer 47

"Cell eating": much larger vesicles are formed called phagosomes - done only by specialized cells

Question 48

What is the extra type of endocytosis in animal cells

Answer 48

Receptor-mediated endocytosis - very selective concentrating mechanisms - requires specialized receptors

Question 49

What particles are involved in pinocytosis

Answer 49

Solutes, fluid, and macromolecules

Question 50

What particles are involved in phagocytosis

Answer 50

Larger particles, other cells, debris

Question 51

What particles are involved in receptor-mediated endocytosis

Answer 51

Particular molecules (ligands) for which the membrane has receptors, and receptors grouped in patches of membranes called "coated pits"

Question 52

What are coated pits

Answer 52

Receptors grouped together in patches of membranes - in relation to receptor-mediated endocytosis

Question 53

What is the site of cellular digestion

Answer 53

Lysosomes

Question 54

What part of the cell membrane is most extensive in terms of surface area

Answer 54

ER

Question 55

If the ER signal sequence in the gene encoding a large protein were deleted, where would the protein end up

Answer 55

In the cytosol

Question 56

If gold nanoparticles are smaller than small proteins, and upon injection into the cell can later be found in the nucleus, how is this explained

Answer 56

Molecules that are small can diffuse non-selectively across the nuclear pore complex

Question 57

Proteins encoded by the nuclear genome destined for the mitochondria, enter the mitochondria via...

Answer 57

Binding to mitochondrial import receptors, unfolding, and passing through translocator proteins in the mitochondrial membrane

Question 58

In eukaryotic cells, RNA polymerase is synthesized by...

Answer 58

Cytosol, by free ribosomes

Question 59

While not actively involved in translation processes, ribosomes...

Answer 59

Are scattered in cytosol, with large and small subunits dissociated from one another

Question 60

Phosphofructokinase, a key enzyme in glycolysis, would reach its destination by...

Answer 60

Having no localization sequence

Question 61

A UPR monitors protein folding in the _______, releasing signals into the _______ that increases the protein folding capacity in the ER

Answer 61

ER lumen, cytosol

Question 62

A cell in which the rate of constitutive secretion secretes rates of pinocytosis...

Answer 62

Increases in membrane surface area

Question 63

What would be the fate of a membrane that is associated with a vesicle that has just secreted its cargo via exocytosis

Answer 63

The vesicle membrane fuses with the plasma membrane and becomes part of it

Question 64

A transmembrane protein destined for the plasma membrane protrudes from the cytosolic face of the ER membrane. On its journey to the destination, where would you expect the protein to protrude?

Answer 64

On the cytosolic face of the Golgi, and the cytosolic face of the plasma membrane