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Biology 360 > Topic 4B - Protein Transport In Mitochondria/Chloroplasts > Flashcards

Topic 4B - Protein Transport In Mitochondria/Chloroplasts Flashcards

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1
Q

Give an example of a plastid which is not a chloroplast

A

Chromoplast

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2
Q

Describe the way that mitochondria reproduce

A

Division by fission - similar to bacteria

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3
Q

Most proteins acting in the mitochondria are synthesized in…

A

The ER/cytosol - transported into the mitochondria

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4
Q

Approximately how many proteins does the mitochondria synthesize that act in the organelle? What are they encoded by?

A

13, encoded by mtDNA

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5
Q

Translated proteins are relocated to the mitochondria through the process of…

A

Post-translational translocation

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6
Q

TOM, TIM, SAM and OXA are all examples of…

A

Beta-barrel transmembrane proteins

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7
Q

Once a proteins has passed through the TOM complex of the outer mitochondrial membrane, where are the three destinations it can go from there?

A
  1. To the SAM complex
  2. To the TIM23 complex
  3. Can be inserted laterally through the TOM complex into the outer mitochondrial membrane
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8
Q

What is the role of the SAM complex?

A

Insert beta barrel proteins into the outer mitochondrial membrane

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9
Q

When a protein passes through the TIM22 complex, where is its final location?

A

Inner mitochondrial membrane

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10
Q

When a protein passes through the OXA complex, where is its final location?

A

The inner mitochondrial membrane

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11
Q

What is the difference between TIM22 and OXA?

A

They both insert proteins into the inner mitochondrial membrane, but the proteins are coming from different locations
TIM22 = from intermembrane space
OXA = from matrix

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12
Q

Describe the state of proteins destined for the mitochondria during transport: are they unfolded or folded?

A

They are unfolded because the folded protein cannot pass through the TOM complex folded

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13
Q

This kind of protein keeps unfolded proteins unfolded to pass through the TOM complex

A

Chaperones

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14
Q

Do TOM and TIM work sequentially or simultaneously?

A

Depends, can do both

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15
Q

Is transport through TOM and TIM active or passive?

A

Active - concentrating proteins inside the mitochondria

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16
Q

What 2 processes drive active transport of proteins into the mitochondria?

A
  1. ATP hydrolysis (outer membrane)

2. Membrane potential (inner membrane)

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17
Q

Describe how “membrane potential” can drive a protein into the matrix from the inner mitochondrial membrane

A

Protons are pumped out of the matrix due to oxidative phosphorylation, therefore the inside of the membrane is more negative than the outside of the membrane. The N-terminal signal sequence is drawn towards the inside of the inner mitochondrial membrane because it is attracted the the negative charge

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18
Q

Is stripping chaperones an active or passive process?

A

Active - requires ATP to take the chaperones away

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19
Q

What is Hsp60?

A

A heat shock protein contained within the mitochondria

Unfolded proteins are contained within the protein and the protein is capped; the cap is released with ATP hydrolysis and the correctly folded protein emerges

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20
Q

In gram-negative bacteria, the equivalent to the mitochondrial SAM complex is…

A

BAM complex

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21
Q

In gram-negative bacteria, the TOM equivalent is…

A

Sec

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22
Q

In a multi-pass transmembrane protein with an internal signal sequence, how does the signal peptidase cleave the sequence?

A

It doesn’t - sequence is spared and is a part of the mature protein

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23
Q

What is the Mia40 complex?

A

Aids in proper assembly of mitochondrial proteins

Oxidizes proteins after they pass through the TOM complex by forming disulfide bonds on the protein, mia is reoxidized and oxidizes the next incoming protein

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24
Q

What are the divisions of the chloroplast from external to internal?

A

Outer membrane, intermembrane space, inner membrane, stroma, thylakoid membrane, thylakoid

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25
Q

Why do proteins destined for the chloroplast have 2 signal sequences? What are they

A

Both N-terminal, have chloroplast signal sequence followed by thylakoid signal sequence, chloroplast sequence is cleaved in the stroma

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26
Q

How many pathways are there for a protein to be transported from the stroma to the thylakoid?

A

4

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27
Q

To cross the inner membrane in chloroplasts (from intermembrane to stroma), what process is used?

A

ATP or GTP hydrolysis

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28
Q

What are the 3 major functions of the ER?

A
  1. Site of lipid biosynthesis
  2. Protein biosynthesis of transmembrane proteins
  3. Storage place for Ca++
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29
Q

Are all transmembrane proteins synthesized in the ER?

A

No, the mitochondria and chloroplast also synthesize some of their own TM proteins

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30
Q

What is the difference between the smooth and rough ER?

A

Rough = presence of ribosomes

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31
Q

The major modification made to most proteins in the ER is the addition of…

A

Sugars

32
Q

How can the ER be isolated?

A

Through a centrifuge - will be in microsome form

33
Q

Is it possible (realistic) to assume all microsomes from a centrifuged sample will be the ER?

A

No - there are many other membranes in the cell

34
Q

The 2 major types of protein translocation are…

A
  1. Cotranslational translocation

2. Post-translational translocation

35
Q

Are ribosomes which produce cotranslational proteins different from ribosomes which produce posttranslational proteins?

A

No - only difference is in the signal sequences

36
Q

Transport into which organelles require chaperones?

A

Chloroplasts and mitochondria

37
Q

Describe the composition of a signal recognition particle (SRP)

A

6 polypeptides wrapped around an RNA molecule

38
Q

Describe the binding pocket of an SRP

A

Largely hydrophobic to interact with hydrophobic signal sequences. Composed of methionines which have simple side chains to accommodate different, bulkier sequences within the binding pocket

39
Q

The signal sequence of a protein destined for the ER usually has a minimum of ( ) hydrophobic amino acids

A

8

40
Q

How many binding sites does an SRP have?

A

2 - one for the signal sequence and one which binds to the ribosome

41
Q

During cotranslation, when the SNP is bound to the signal sequence and the ribosome of a polypeptide, other than relocating to the ER what happens?

A

Translation of the protein pauses

42
Q

When the SNP is bound and headed towards the ER - describe its binding to the ER

A

Binds to SRP receptor which is associated with a protein translocator

43
Q

What is the role of the protein translocator?

A

Acts as a channel for the protein to be synthesized through, transports the growing polypeptide into the ER lumen

44
Q

What are the two ways the protein translocator can open?

A
  1. Opens a pore for hydrophilic parts of the protein

2. Opens laterally to insert TM regions into the ER membrane

45
Q

Proteins that are meant to stay within the ER contain this:

A

ER retention signal

46
Q

What 2 elements does the ER signal sequence bind to?

A
  1. SRP

2. Protein translocator

47
Q

Once a protein reaches the protein translocator in the ER, the signal sequence is cleaved and…

A

Degraded, if no longer needed

48
Q

If “start” and “stop” segments of a transmembrane protein are swapped out, does the protein still assemble properly?

A

Yes - as long as they are relatively similar hydrophobic regions with similar functions

49
Q

Where are ER retention signals on a protein?

A

At the c-terminus

50
Q

What is the function of the Get1-Get2 complex?

A

Insert C-terminal-anchored membrane proteins into the ER membrane

51
Q

What is the function of the Get3 ATPase?

A

Targeted by the Get1-Get2 complex to form the Get1-Get2-Get3 complex. It hydrolyses its ATP to disassemble the whole complex

52
Q

In order for a c-terminal ER retention signal to be brought to Get3, what intermediate is required?

A

A pre-targeting complex recognizes the signal and brings it to Get3

53
Q

How many proteins produced in the ER are glycosylated (%)

A

50%

54
Q

What is the role of oligosaccharyl transferase?

A

Transfers lipid-linked oligosaccharides onto proteins to be glycosylated

55
Q

The interface between a protein to be glycosylated and the oligosaccharide is…

A

An asparagine side chain

56
Q

What is the function of the oligosaccharides added in the ER?

A

Aid in protein folding

57
Q

The first sugars to be cleaved from a “young” oligosaccharide are…

A

Glucoses

58
Q

Mannose sugar groups are cleaved from an oligosaccharide chain in this organelle

A

The golgi

59
Q

The asparagine and oligosaccharide chains of a glycosylated protein are ( )-linked

A

N-linked

60
Q

What is the role of glycosylation?

A

Ensure proper folding of a protein and determine its final 3D structure

61
Q

What is the difference between calnexin and calreticulin?

A 
Calnexin = membrane-bound
Calreticulin = soluble ER resident protein

Both are thought to perform the same role

62
Q

What is the role of calnexin? What kind of protein is it?

A

Chaperone protein

Bind oligosaccharides of incompletely-folded protein to retain them within the ER, prevent unfolded proteins from clumping together irreversibly

63
Q

Which ER protein checks proteins leaving the ER to see if they have been correctly folded?

A

Glucosyl transferase

64
Q

What does glucosyl transferase do when it encounters an incorrectly-folded protein?

A

Adds a glucose group to it to retain it in the ER

65
Q

Glucoses are added by glycosyl transferases by taking them from…

A

UDP (Uridine diphosphate) bound to glucose

66
Q

A complex involving what elements bind to a misfolded protein to export it to the cytosol?

A

Chaperones, disulfide isomerase, lectin

67
Q

In the export of misfolded proteins to be degraded, lectin binds to…

A

The remainder of the oligosaccharide chain of a misfolded protein

68
Q

Why are chaperones necessary in the export of misfolded proteins?

A

Proteins need to be exported through a pore, so chaperones help keep it in its primary stage

69
Q

Is the transport of misfolded proteins out of the ER active or passive?

A

Active - goes thru a channel!

70
Q

What enzyme is responsible for removing sugar groups off a misfolded protein?

A

N-glycanase

71
Q

What helps a proteasome recognize proteins which need to be degraded?

A

Ubiquitin - misfolded proteins are ubiquinated as they leave the ER

72
Q

If a protein is leaving the ER to go to the cytosol, what can we say about this protein?

A

It is likely misfolded/to be degraded - almost NO cytosolic proteins are synthesized outside of the cytosol

73
Q

How can the degradation mechanisms for cellular proteins be helpful for the survival of viruses?

A

Can use this machinery to degrade immune proteins

74
Q

The process of sending proteins out of the ER into the cytosol is called…

A

Retrotranslocation

75
Q

What is an example of a situation where splicing mRNA does not happen in the nucleus?

A

The IRE1 pathway in the misfolded/unfolded protein response - splicing happens in the cytosol

Biology 360 (12 decks)

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