MCB Lecture 31 Gated Transport & Transmembrane Transport Flashcards Preview

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Flashcards in MCB Lecture 31 Gated Transport & Transmembrane Transport Deck (35)
0

How do molecules get in and out of the nucleus?

Gated transport

1

Describe the structure of a nuclear pore

Octamer: eight proteins line the pore complex

2

How do larger molecules get across the nuclear envelope?

Need a translocator

1. Nuclear Localisation Sequence found in protein
2. Nuclear Import Receptor recognises the NLS
3. Protein is shuttled through the Nuclear Pore Complex on the Nuclear Import Receptor
4. Ran-GTPase hydrolysis GTP, cargo dissociates in the nucleus
5. GDP dissociates on the cytosol side

3

What is the name of the sequence that is recognised on a protein for its import into the nucleus?

Nuclear localisation sequence

4

What is the name of the receptor that moves proteins into the nucleus?

Nuclear import receptor

5

What are the features of the nuclear localisation sequence?

Lysine rich
15-60 amino acids long

6

Describe the steps involved with exporting a protein from the nucleus

Same as the import, except the protein binds to the Nuclear Import Receptor on the inside, as well as Ran-GTP.
Ran-GTP is hydrolysed in the cytosol, and the cargo is released

7

Describe the function of Ran-GTPase

Hydrolysis GTP in the cytosol

8

Where are nuclear proteins synthesised?

In the cytosol

9

When do nuclear proteins fold?

In the cytosol

10

How is the import of nuclear proteins regulated?

Phosphorylation of a protein causes conformational change, and the Nuclear Localisation Sequence is exposed
Now, the protein can be imported

11

When is transmembrane transport used?

To move protein from the cytosol into the mitochondria or ER

12

Describe how proteins traverse the two mitochondrial membranes

1. Signal sequence on protein recognised by the TOM receptor
2. TOM and TIM line up in the membranes -> translocation channel
3. The protein is fed through into the matrix of the mitochondria
4. Signal sequence cleaved
5. Protein folds

13

Describe the features of the signal sequence for proteins entering the mitochondria

The signal sequence is an amphiphilic sequence.
The receptor I recognises the hydrophobic region

14

Describe the structure of the translocation channels on the mitochondrial membrane

TOM on outer membrane
TIM on inner membrane

15

How do proteins get into the peroxisomes?

Translocators. The mechanism is not well understood

16

What is cotranslational translocation?

This is when a protein is fed into the ER while it is still being translated

17

What is the sequence that is recognised on a protein so that it many enter the ER?

Signal sequence

18

What is the signal recognition particle?

This is a separate protein that binds to the signal sequence on a protein that is being fed into the ER
When is binds, it is then recognised by the Signal Recognition Particle Receptor
The protein is fed through the translocator

19

What is the Signal Recognition Particle Receptor?

This recognises the Signal Recognition Particle bound to the signal sequence of a protein being translated

20

What is Sec61?

This is the translocator complex and the ribosome in the ER membrane

21

Which types of proteins are fed through an ER translocator?

Soluble proteins

22

What is signal peptidase?

Cleaves the signal sequence, so that the protein is free in the lumen of the ER

23

Where do ER proteins fold?

In the lumen of the ER

24

What are the two binding sites on the Nuclear import receptor?

What is special about the binding sites?

1. Cargo binding domain
2. Ran binding domain

The nuclear import receptor can only bind one of these at a time

25

What is Ran?

It is a protein that binds GTP and hydrolysis it.

It is important in the movement on proteins in and out of the nucleus

26

What sort of molecules are shuttled across the nuclear pore by nuclear import and export receptors?

Proteins

27

What is the name of the receptor that exports proteins from the nucleus across the nuclear pore complex?

Nuclear export receptor?

28

How does binding of RAN-GTP differ in nuclear export and import?

It doesn't
It binds in the nucleus, moves across and hydrolysed and dissociates in the cytosol

29

What is interesting about the NFAT protein that is shuttle across the nuclear pore?

The NLS is cryptic, but is revealed when phosphorylated by a Ca2+ kinase

Thus nuclear import is regulated and calcium dependent

30

How is it ensured that mitochondrial proteins do not fold before they enter the mitochondria?

Chaperones bind to them

31

What is the structure of the signal sequence of a protein that is recognised by the translocator receptor?

It is an alpha helix

32

Which proteins enter the ER?

Secreted
Proteins destined for membrane embedding
Proteins bound for lysosomes, Golgi and ER

33

Describe the locations involved for translation of proteins that are bound for the ER

Initiation: ALWAYS in the cytosol on free ribosomes
Termination: ribosomes bound to the endoplasmic reticulum

34

How does the signal sequence of proteins bound for the ER associate with the ER?

Signal recognition particle (SRP)

SRP receptor protein

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