Cell Bio Exam 2 Lecture 7

Question 1

Signal sequences that direct proteins to the correct compartment are _______.

Answer 1

encoded in the amino acid sequence of the protein

Question 2

proteins without
sorting signals will
by default remain in the

Answer 2

cytosol

Question 3

3 major sorting choices or paths in eukaryotic cells:

Answer 3

Transport through nuclear pores, Transport across membranes, Transport by vesicles

Question 4

Where do signal sequences occur?

Answer 4

primary and secondary structures of polypeptides

Question 5

T or F. The internal compartments of the eukaryotic cell such as the ER, mitochondria, Golgi and endosomes are believed to be derived from endosymbionts

Answer 5

False

Question 6

two suspected origins for the evolution of internal membrane compartments:

Answer 6

plasma membrane invaginations (endomembrane system) and endosymbionts (mitochondria and chloroplasts)

Question 7

What two things are endosymbionts?

Answer 7

Mitochondria and chloroplasts

Question 8

Sorting and trafficking processes require

Answer 8

require energyinputs to move proteins across membranes andto deform and separate or fuse membranes

Question 9

NLS receptors use

Answer 9

GTP hydrolysis

Question 10

T or F. Once proteins are transported into the nucleus, they cannot be exported to the cytosol again

Answer 10

False

Question 11

T or F. Once proteins are transported into the ER lumen, they can be exported to the cytosol again

Answer 11

False

Question 12

T or F. Proteins that are transported into both the ER and the nucleus are unfolded as they move across the compartment membranes

Answer 12

False

Question 13

what allows proteins and mRNAs to traffic across the nuclear membrane

Answer 13

Nuclear Pore Complexes

Question 14

Nuclear Pore Complexes allows ____ and ______ to traffic across the nuclear membrane

Answer 14

proteins and mRNAs

Question 15

NLS sequences of “nuclear” proteins associate with _______ which move the cargo across the nuclear membrane in ________

Answer 15

NLS receptors, GTP dependent manner

Question 16

T or F. Nuclear import signals are typically hydrophobic signal sequences present at the NH2 end of the proteins.

Answer 16

False

Question 17

Nature of NLS is a

Answer 17

a string of basic amino acids

Question 18

Proteins are unfolded as they are transferred
across the

Answer 18

mitochondrial membrane

Question 19

When proteins are unfolded as the transfer acorss the mitochondrial membrane, the signal sequence gets removed by

Answer 19

signal peptidase

Question 20

What is the Mitochondrial signal sequence?

Answer 20

an amphipathic alpha helix

Question 21

Transport of proteins into the ER occurs:

Answer 21

during translation of the protein

Question 22

Proteins being made can be directed for translocation into the ER by:

Answer 22

Signal Recognition Particle (SRP) and the SRP receptor and a translocation channel

Question 23

What does the Signal Recognition Particle (SRP) do?

Answer 23

associates with the nascent signal sequence, stalls the ribosome and aids in docking on the ER membrane at the SRP receptor

Question 24

Proteins are modified by _____ in the ER and Golgi

Answer 24

glycosylation

Question 25

_______ is also catalyzed inthe ER.

Answer 25

Disulfide bond formation

Question 26

T or F. Signal sequences causing transport of some proteins entering the ER or Mitochondria can be cleaved from the proteins once they enter these compartments

Answer 26

True

Question 27

The N-terminal signal sequence of many secretory
proteins is cleaved off by a

Answer 27

signal peptidase

Question 28

Start transfer and Stop transfer sequences specify insertion of ______ into the ER membrane
for single and multipass transmembrane domain proteins

Answer 28

hydrophobic transmembrane helices

Question 29

Bacteriorhodopsin is an example of a

Answer 29

multipass TM protein

Question 30

_______ have helped to study the nature of the signals, their recognition and import processes

Answer 30

Cell free reconstituted systems

Question 31

Addition of glycosylations by _______

Answer 31

oligosaccharide protein transferases

Question 32

Protein folding in the ER is monitored and assisted
by ______before the mature proteins
are permitted to be trafficked out of the ER

Answer 32

chaperone proteins

Question 33

The Unfolded Protein Response (UPR) pathway is an example of a ______ that helps cells _________ by ________

Answer 33

signaling pathway that helps cells maintain quality control over protein folding and biogenesis by increasing chaperone activities.

Question 34

Cystic fibrosis is frequently caused by the fact that

Answer 34

quality control at the ER by chaperones is extremely stringent

Question 35

misfolded proteins are

Answer 35

rapidly degraded

Question 36

secretory pathway
“forward” flow =

Answer 36

ER -> Golgi -> Plasma Membrane
->Lysosome

Question 37

Which of the following proteins serves to allow transport vesicles to recognize the correct membrane they will dock to:

Answer 37

tSNARES

Question 38

v-SNARE is found on the

Answer 38

vesicle

Question 39

t-SNARE is found

Answer 39

the target membrane/compartment (t for target)

Question 40

What do Rabs do?

Answer 40

Recognize tethers

Question 41

The pH of the lysosome is:

Answer 41

Lower (more acidic) than the cytosol