Protein Targeting: Mitochondria, Chloroplasts, & Peroxisomes

Question 1

TRUE OR FALSE:
Mitochondria, Chloroplasts, and Peroxisomes are all enclosed by a SINGLE membrane?

Answer 1

False.
Mitochondria & Chloroplasts - DOUBLE
Peroxisomes - SINGLE

Question 2

Where are the proteins found in the Mitochondria and Chloroplasts synthesised?

Answer 2

Synthesised by ribosomes in the cytosol

Question 3

How are proteins imported into the Mitochondria and Chloroplasts?

Answer 3

Post-translationally

Question 4

Where does translocation of proteins to the matrix occur in mitochondria?

Answer 4

At contact points
(where the inner and outer membrane are close together)

Question 5

What are the proteins involved in protein translocation across the OUTER membrane called?

Answer 5

TOM
Translocon of Outer Membrane

Question 6

What are the proteins involved in protein translocation across the INNER membrane called?

Answer 6

TIM
Translocon of Inner Membrane

Question 7

How are proteins synthesised in the cytosol kept unfolded before translocating the mitochondrial matrix?

Answer 7

Kept unfolded by chaperones (Hsc70)

Question 8

What THREE places during protein translocation into the mitochondria is energy needed?

Answer 8

1. Binding of Hsc70 to protein in cytosol
2. Binding of Hsc70 to protein in matrix
3. Proton motive force across inner membrane

Question 9

Which protein recognises transmembrane segments within a translocated protein and inserts it into the inner membrane of the mitochondria?

Answer 9

Oxa1

Question 10

What is the name of the import receptor involved in the targeting of proteins to the inner mitochondrial membrane for multi-pass transmembrane proteins?

Answer 10

TOM70

Question 11

What is the name of the inner membrane channels involved in the translocation of matrix proteins to the inner mitochondrial membrane for multi-pass transmembrane proteins?

Answer 11

TIM22 / TIM54

Question 12

What is the name of the TWO intermembrane proteins required for the transfer of proteins from the outer membrane to the inner membrane in mitochondria?

Answer 12

TIM9 / TIM10

Question 13

What TWO sequences do Mitochondrial Outer Membrane proteins contain?

Answer 13

1. A short ‘matrix’ targeting sequence
2. A long hydrophobic sequence

Question 14

What does the Long Hydrophobic protein sequence do in the Mitochondrial Outer Membrane?

Answer 14

• Stops the transfer through the outer membrane
• Is the transmembrane helix that anchors the protein in the membrane

Question 15

What are the FOUR major structures within Chloroplasts?

Answer 15

1. Outer membrane
2. Inner membrane
3. Stroma
4. Thylakoid membrane

Question 16

Where in the Chloroplast does light absorption and ATP, NADPH synthesis occur?

Answer 16

Thylakoid membrane

Question 17

Where in the Chloroplast does CO2 fixation occur?

Answer 17

Stroma

Question 18

Which amino acids is the N-terminal stromal import signal rich in?

Answer 18

• Serine
• Threonine
• Small hydrophobic residues

Question 19

What are the functional analogues of TOM and TIM in chloroplasts?

Answer 19

TOC & TIC

Question 20

What protein binds Peroxisomal Targeting Sequence 1 (PTS1)?

Answer 20

Pex5

Question 21

Which receptor does Pex5 interact with in the peroxisomal membrane?

Answer 21

Pex14

Question 22

Where is the protein + Pex5 complex transferred to in the peroxisomal membrane?

Answer 22

Pex2 / Pex10/ Pex12

Question 23

What type of enzyme converts H2O2 to H20 + O2 in the peroxisome?

Answer 23

Catalase

Question 24

What are TWO examples of Peroxisome Biogenesis Disorders?

Answer 24

1. Zellweger Syndrome
2. Adult Adrenoleukodystrophy (ALD)