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BIOSCI 201 > Lecture 5 > Flashcards

Lecture 5 Flashcards

1
Q

What causes a polypeptide to be sent to the ER?

A

Detection of a signal sequence by SRP (signal recognizing protein)

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2
Q

What type of translation is used in insert of polypeptides to the ER?

A

Co-translational transport

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3
Q

What is the signal sequence used to target proteins to the ER?

A

A large hydrophobic region at the N terminus

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4
Q

What is the receptor for ER targeted proteins once they have bound SRP?

A

The alpha domain of the SRP receptor

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5
Q

What is the translocon for ER targeted proteins?

A

Sec 61-Alpha

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6
Q

What happens to the signal sequence of an ER targeted protein?

A

It is cleaved by a signal peptidase

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7
Q

What molecular chaperone pulls the ER targeted protein into the lumen and prevents misfolding?

A

BiP

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8
Q

What is the energy source for ER targeted proteins?

A

GTP

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9
Q

What is the energy source of the BiP protien?

A

ATP

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10
Q

When does insertion of a mitchondrial protein occur?

A

Once the protein has already been fully transcribed BUT has not folded

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11
Q

What prevents mitochondrial proteins from folding before they are inserted?

A

HSC70

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12
Q

What is the signal sequence for mitochondrial targeting?

A

A 20-50 residue long amphipathic alpha helix at the N terminal

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13
Q

What are the receptors for mitochondrial targeted proteins?

A

TOM 20/22 for the outer membrane, TIM 44 for the inner membrane

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14
Q

What is the translocon for the outer membrane of the mitochondria?

A

TOM 40

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15
Q

What is the translocon for the inner membrane of the mitochondria?

A

TIM 23/17

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16
Q

Which region of the mitochondria do matrix targeted proteins enter from the cytosol?

A

At contact sites where the two membranse of the mitochondria almost touch

17
Q

What happens to the signalling sequence for mitochondrial matrix proteins?

A

It is cleaved by a matrix processing protease?

18
Q

What happens to the sequence for the intermembrane space?

A

It is cleaved by a protease in the intermembrane space

19
Q

Where does the energy for import of mitochondrial proteins come from?

A

ATP hydrolysis by chaperone proteins and H+ gradient for transport across the intermembrane space

20
Q

What is the difference in transport between an intermembrane protein and matrix protein?

A

A matrix protein is ‘pulled’ across the inner membrane by matrix HSC70, intermembrane proteins enter the TIM 23/17 translocon, then stop moving across due to the signal sequence, moving out of the translocon where a inter-membrane protease removes the rest of the coding sequence by cleaving the polypeptide at the level of the inner membrane

21
Q

What is a peroxisome?

A

A cell organelle which contains oxidative enzymes useful for the dgradation of fatty acids

22
Q

What is the signal for peroxisome targeted proteins?

A

Ser-Lys-Leu (SKL Sequence) at the C terminal of the protein

23
Q

What recognises the signal sequence for peroxisome targeted proteins?

A

Pex 5 recognises the protein in the cytosol which then binds to Pex14 on the perioxisome membrane

24
Q

Where does the peroxisome targeted protein and pex 5 dissociate?

A

Once they have both entered the perioxisome

25
Q

What is the translocon complex for protine insertion into peroxisomes?

A

A complex of pex 2, 10, 12

26
Q

Where does the energy for import of polypeptides into peroxisomes come from?

A

ATP

27
Q

What happens to the signal sequence for peroxisome targeted proteins?

A

It becomes incorporated into the protein sequence

28
Q

What is the signal sequence for nuclear targeted proteins?

A

Nuclear Localisation sequence at the N terminal, usually rich in lysine and argnine

29
Q

What state are proteins transported into the nucleus in?

A

Fully folded functional proteins

30
Q

What recognises the nuclear localisation sequence?

A

Importin

31
Q

What protein enables the importin-nuclear targeted protein to move across the nuclear pore?

A

Ran-GDP

32
Q

What happens to the the Ran-GDP protein inside the nucleus?

A

GTPase exchange factor exchanges its bound GDP for a GTP allowing it to bind to the importin and ferry it to the cytoplasm via the nuclear pore

33
Q

What is the energy source for nuclear targeted protein transport?

A

None (other than the GTP required to bring the importin back out into the cytoplasm

34
Q

Identify the transport Proteins

A
35
Q

What type of membrane protein is this?

A
36
Q

What type of membrane protein is this?

A
37
Q

What type of membrane protein is this?

A
38
Q

What type of membrane protein is this?

A

BIOSCI 201 (12 decks)

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