Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biochemistry Exam 3 > Intracelluar Compartents and Protein Sorting > Flashcards

Intracelluar Compartents and Protein Sorting Flashcards

0
Q

N terminal ER signal sequence at beginning of a cytosolic protein would lead to what result?

A

Redirectrion from cytosol to the ER for secretion from cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
1
Q

How are proteins sorted generally?

A

Signal sequences

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Where are signal sequences most often found?

A

N-terminal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are signal peptidases?

A

Removes signal sequence from the finished protein core once the sorting process is complete

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is a signal patch?

A

Sorting signal composed of multiple internal amino acid sequences that form a three-dimensional arrangement of atoms on protein surface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe the specificity of sorting receptors for protein signal sequences

A

Usually on a protein class level

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

T or F: Orientation of proteins is maintained in budding and fusing of vacuoles

A

T, always maintain same domains facing the cytosol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Gated transport controls what exchange?

A

Between nucleus and cytosol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Transmembrane transport occurs between what?

A

Cytosol and Mitochondria/peroxisomes/plastids/ER

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Vesicular transport occurs between what?

A

ER, Golgi, Endosomes, Lysosome, Secretory vesicles, Cell exterior

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Proteins without a sorting signal end up where?

A

Cytosol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Where does protein synthesis begin?

A

Ribosomes in cytosol (except for mitochondrial ribosomes)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

T or F: Translocation to the ER is co-translational

A

T

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Resident ER, Golgi resident, plasma membrane proteins, secreted proteins, and lysosomal proteins are initially synthesized where?

A

RER

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Where does glycosylation take place?

A

ER and Golgi

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

T or F: Proteins in cytosol, mitochondria, peroxisome, and nucleus are glycosylated

A

F

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Proteins synthesized on free ribosomes are directed where when they lack ER translocation signal peptides?

A

Mitochondria, peroxisomes, or nuclei if have signal

Cytosol otherwise

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Describe the structure of the nuclear envelope

A

Double membrane penetrated by pores in which nuclear pore complexes are positioned. It is contiguous with the ER.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Describe the inner nuclear membrane

A

Specific proteins that act as anchoring sites for chromatin and for the nuclear lamina.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Describe the outer nuclear membrane

A

Continuous with the membrane of the ER and is studded with ribosomes engaged in protein synthesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Where are histones/DNA/RNA polymerases/gene regulatory proteins. and RNA processing processes all made?

A

Cytosol. imported into the nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Where are tRNA and mRNA made?

A

Nucleus and exported to the cytosol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Describe the makeup of the nuclear porin complex

A

30 or so different NPC proteins or nucleoporins. Multiple copies i a octagonal symmetry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

T or F: Small water soluble molecules can diffuse passively through the NPC

A

T

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the cut off for passive diffusion through the NPC?

A

60,000 daltons or so

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is responsible for the selectivity of active nuclear import processes?

A

Nuclear localization signals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Describe the typical makeup of a nuclear localization signal

A

1-2 short sequences rich in positively charged lysine and arginine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

T or F: Unfolding is required to move a protein into/out of the nucleus

A

FALSE, can be moved fully assembled/folded

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What recognizes nuclear localization signals?

A

Nuclear import receptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Describe the function and specificity of nuclear import receptors

A

Recognize specific signals. Receptors bind to both the signal sequence and the protein to transport. Fibrils on the NPC are rich in phenylalanine and glycine, called FG repeats. These bind to the import receptors and move to next FG repeat and transfer the protein. continues all the way to the interior nuclear cytosol. Receptors are recycled

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is responsible for nuclear export similar to nuclear import proteins?

A

Nuclear export signals and nuclear export receptors

31
Q

What is the function of Ran?

A

Required for nuclear import and export

32
Q

Describe the function of Ran

A

GTPase found in cytosol and nucleus. Ran-GTP/Ran-GDP act as molecular switches. Ran-GTP is dense in the nucleus and Ran-GDP is dense in the cytosol. Gradient helps with nuclear import/export

33
Q

Where is Ran-GDP located? What makes it?

A

Cytosol; Ran-GAP dephosphorylates Ran-GTP

34
Q

Where is Ran-GTP located? What makes it?

A

Nucleus; Ran-GEF on chromatin exchanges Ran-GDP for Ran-GTP

35
Q

Describe how Ran helps with nuclear transport

A

Export: Ran-GTP hops on to cargo and causes release in cytosol to Ran-GDP via Ran-GAP
Import: Ran GDP hops on to cargo and causes release in nucleus to Ran-GTP via Ran-NEF

36
Q

Describe where mitochondrial proteins are translated

A

First in the cytosol as mitochondrial precursor proteins and then translocated to the mitochondria by post-translational mechanism

37
Q

Describe mitochondrial signal sequences

A

Amino terminal leader sequence up to 70 AA in length (not highly conserved) with many positively charged AA (lysine/arginine)

38
Q

Describe the translocation of proteins to the mitochondria

A

Translocation is not co-translational. Proteins are in unfolded state. Requires ATP and chaperone proteins. Uses TOM and TIM because of two layers of membrane.

39
Q

T or F: Mitochondrial translocation is co-translational

A

F, no translation is taking place. Were fully synthesized as mitochondrial precursor proteins

40
Q

Where are peroxisomal proteins synthesized?

A

Cytosol

41
Q

What is characteristic of a peroxisomal signaling sequence?

A

Three AA on the C-terminal.

42
Q

T or F: Peroxisomal proteins are imported without unfolding

A

T; imported as fully folded proteins

43
Q

What is the function of ER?

A

Lipid and protein biosynthesis

44
Q

T or F: Import of proteins into ER is co-translational

A

T

45
Q

T or F: Import into the nucleus, mitochondria, and peroxisome is post-translational

A

T

46
Q

Why is the rough ER rough?

A

Studded with ribosomes that allow for co-translational translocation

47
Q

What are microsomes?

A

Small closed vesicles that are formed when the ER is disrupted by homogenization. RER microsomes are more dense than SER microsomes

48
Q

Describe the Blobel and Dobberstein experiment

A

Added microsomes to mRNA systems in-vitro. Found that proteins were smaller with RER than they were without. Cleavage of the signal sequence.

49
Q

What is the signal hypothesis?

A

Leading signal sequence directs secreted protein to ER membrane and is cleaved off by signal peptidase in ER membrane before the polypeptide chain is completed

50
Q

What is a SRP?

A

Signal recognition protein. Cycles between ER and cytosol binding to the signal sequence and the SRP receptor in the ER membrane. SRP are complex and made up of 6 different polypeptides bound to single small RNA molecule

51
Q

Describe the ER signal sequence

A

Variable, but has 8 or more nonpolar AA at center.

52
Q

Describe the recognition pocket of SRP

A

Large hydrophobic pocket lined with methionines and can accommodate hydrophobic signals or all sizes shapes and compositions

53
Q

Besides localization, what other function does SRP perform?

A

Pauses translation until the ribosome binds to the ER membrane. Continues translation then. Ensures that protein isn’t released to the cytosol

54
Q

Describe the overall process of ER localization of proteins

A

SRP binds to protein sequence, SRP binds to SRP receptor on ER, ribosome binds to ER and continues translation into the ER lumen releasing SRP and SRP receptor complex

55
Q

What are the two populations of ribosomes?

A

Membrane bound - attached to the cytosolic side of ER and engaged in ER translocated proteins
Free - unattached to any membranes, synthesize all other proteins not destined for ER.
ONLY differ in the type of proteins being made

56
Q

What is Sec61?

A

A gated protein that imports into the ER when signal peptide is present

57
Q

Signal sequences are recognized twice for ER translocation. Describe.

A

SRP in the cytosol.

Binding site in the pore of protein translocator to serve as a start-transfer signal to open the pore

58
Q

Describe how a single pass membrane protein is synthesized

A

A secondary hydrophobic segment in the protein stops the transfer process of the protein before total translocation. This stop-transfer signal anchors the protein in the membrane. N terminal is on the lumenal side and C terminus is on cytosolic side

59
Q

ER signal sequences are located on what terminal

A

N terminal

60
Q

Peroxisome recognition sequences are on what terminal?

A

C terminal

61
Q

Mitochondrial recognition sequences are on what terminal

A

N terminal

62
Q

How are internal signal sequence proteins inserted into the ER membrane?

A

Same mechanism as if on N-terminal end. Brought by SRP to ER. Can make the N or C terminal on the ER lumen side depending on the nearby charged amino acids.

63
Q

T or F: N or C terminals can be on the lumen side of an ER integrated protein

A

T, if via an internal signal sequence. Only N if the sequence is on N terminal

64
Q

Directionality of protein synthesis?

A

N to C

65
Q

How are multi-pass proteins integrated?

A

Internal signal sequences serve to start-transfer until a stop-transfer is encountered. Multiple start- and stop-transfer sequences

66
Q

What is ERAD?

A

ER-associated degradation pathway. Quality control system that identifies misfolded proteins and transports them to cytosol and targets them for proteasome degradation.

67
Q

Describe the link between Parkinson’s disease and ERAD

A

Parkin, E3 ubiquitin ligase is mutated. An unfolded protein leads to ER stress.

68
Q

Describe the link between ERAD and CF

A

Mutant misfolded protein in the ER is not recognized by mutation in CFTR (phenylalanine deletion at position 508). Loss of chloride regulation in CFTR expressing cells

69
Q

Function of Golgi

A

Stacked disks of membranes with lots of vesicles. Each stack has a cis and trans face. Cisternae in each disk make up the cis and trans Golgi networks. Glycosylation occurs here.

70
Q

Three major classes of glycoproteins

A

O-linked - hydroxyl chains of serine or threonine and a sugar
N-linked - those with N-glycosidic linkage involving asparagine
GPI-anchored - carboxyl terminal AA of a protein via a phosphorylethanolamine joined to oligosaccharide. Linked via glucosamine to phosphatidylinositol (PI)

71
Q

N-linked glycoproteins have what common core?

A

Man3GlcNAc2 = 3 mannose in a branch attached to two n-acetylated glucosamines in series attached to a asparagine

72
Q

What sequence after the signal peptide signals for glycosylation?

A

Asn-X-Thr/Ser where X can be anything except proline

73
Q

What is the first step of N-linked glycosylation?

A

Dolichol-P-P-oligosaccharide transfers the oligosaccharide to Asn (membrane bound enzyme)

74
Q

What does tunicamycin do?

A

Drug that inhibits the synthesis of the dolichol-oligosaccharide donor so no N-linked glycosylation occurs.

75
Q

Where are high-mannose or complex oligosaccharides formed?

A

In the golgi, post-processing after the ER glycosylation

76
Q

What is GPI-linked glycoprotein? Where is it located? Synthesis?

A

Glycosylphosphatidylinositol linked glycoproteins on the outer leaflet of the plasma membrane anchored to PI (i.e. on the lumen side of the ER).
Synthesis begins in ER and GPI anchor is assembled separately and attached to the carboxyl terminal end of the protein after cleavage of the preexisting C terminal end

Biochemistry Exam 3 (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions