Protein sorting

Question 1

What are imported into the nucleus

Answer 1

Histones, transcription factors, DNA/RNA polymerases, RNA splicing factors, DNA repair enzymes

Question 2

What are exported from nucleus?

Answer 2

mRNA, tRNA, ribosomal subunits, shuttling proteins

Question 3

What perforates the nuclear envelope?

Answer 3

Nuclear pore complex

Question 4

What type of arrangement does the NPC have and what else?

Answer 4

Octagonal arrangement
Central aqueous pore
Many individual proteins

Question 5

Small molecules pass through pores how?

Answer 5

freely by diffusion

Question 6

How do large molecules get into the nucleus?

Answer 6

Active transport

Question 7

Nuclear proteins complete synthesis where and pass through pores how?

Answer 7

Complete synthesis on cytosolic ribosomes and pass through pores in fully folded state

Question 8

How do the right proteins get into the nucleus? what allows them to be targetted to the nucleus

Answer 8

Nuclear localisation signals sequences

Question 9

What makes up the NLS Sequences

Answer 9

A continuous stretch of amino acids 15-60 residues long

Question 10

Where are the NLS sequences?

Answer 10

Near the N terminal
OR
A signal patch where there are multiple internal sequences in the unfolded protein which then combine to form a signal patch in the folded protein form

Question 11

The NLS sequences are recognised by what?

Answer 11

Complementary receptors

Question 12

Nuclear localisation requires an intact and functional what?

Answer 12

NLS

Question 13

A sequence rich in what amino acid targets a protein to the nucleus?

Answer 13

Lysine rich

Question 14

Mutation of Lysine rich sequence to what causes cytoplasmic retention?

Answer 14

Lysine to Threonine

Question 15

A cargo protein has what on it?

Answer 15

NLS

Question 16

The nuclear import receptors recognises and binds to what?

Answer 16

NLS on the cargo protein

Question 17

Nuclear import receptors interact with what to transfer cargos in and out of the nucleus?

Answer 17

Interact with the nuclear pore complex

Question 18

Describe the binding and dissociation of nuclear import receptors to NPC transports cargo into nucleus

Answer 18

1. Cargo with NLS binds NIR
2. NIR shutles into the nucleus via the NPC (FG repeats)
3. Ran GTP binds to NIR to discharge the cargo
4. NIR shuttles out of the nucleus via NPC with the RanGTP bound (FG repeats)
5. Ran GTP is hydrolysed to Ran GDP in the cytosol
6. NIR is free to shuttle more cargo into the nucleus

Question 19

Ran GDP is found where and where is Ran GTP

These two forms confer on what?

Answer 19

Ran GDP is in cytosol
Ran GTP is in nucleus
Confers directionallity on transport

Question 20

Name a way nuclear protein can be regulated

Answer 20

Via NFAT, transcription factor found in the cytoplasm

NLS in NFAT is cryptic but exposed after phosphorylation of amino resides (Ser) by a ca2+ regulated kinase.

Question 21

Phosphorylation of NLS in NFAT produces what?

Answer 21

a conformational change

Question 22

Mitochondrial proteins are imported how?

Answer 22

Fully synthesised but unfolded polypeptide chains and chaperones prevent folding.

Question 23

What are the signal sequences like in mitochondrial translocation?

Answer 23

Amphiphillic, forms an alpha helix with hyophobic, polar and hydrophillic residues on separate side of the helix

Question 24

Hydrophobic region matches what on the receptor for mitochondria?

Answer 24

Matches hydrophobic groove of receptor

Question 25

What moves the mitochondrial proteins through both membranes?

Answer 25

Protein translocators

Question 26

Where are TOM and SAM located?

Answer 26

Outer mitochondrial membrane

Question 27

Where are TOM, TIM and OXA located?

Answer 27

Inner mitochondrial membrane

Question 28

The following complexes insert protein into where? 1) TOM 2) SAM 3) TIM 4) OXA

Answer 28

1) Proteins into outer membrane 2) Outer membrane 3) Inner and matrix and inserts mitochondrial derived proteins into inner membrane 4) Inner membrane and matrix

Question 29

Describe how a protein gets into the mitochondrial matrix?

Answer 29

1) Precursor unfolded protein binds to the import receptor in TOM complex. 2) Passes through the outer mitochondrial membrane and into the inner membrane via the TIM complex . 3) Once in the matrix, signal peptidase cleaves off the signal on the protein and it is folded into a stable structure to produce a mature mitochondrial protein

Question 30

Mitochondrial import requires what?

Answer 30

Energy ATP

Question 31

Describe how chaperones and ATP is involved in mitochondrial protein import

Answer 31

Chaperone proteins (Cytoplasmic Hsp70) binds to precursor peptide. The release requires ATP hydrolysis to push protein through TOM complex. Import via TIM results in mitochondrial Hsp70 binding ATP hydrolysis pulls protein through TIM complex

Question 32

Synthesis of ER targeted proteins begins where and completed when?

Answer 32

Begins on free ribosomes in cytosol but translation is completed after ribosome binds to ER

Question 33

What directs ER signal sequence to specific receptor in ER membrane

Answer 33

Signal recognition particle

Question 34

Describe the process of directing a signal polypeptide to the ER membrane

Answer 34

do again