Transport into mitochondria + peroxisomes Flashcards

Semester 1 year 1

1
Q

What is the function of the mitochondria?

A

-energy production by making large amounts of ATP
-produces a H+ grad across the inner mito membrane, which drives ATPase
-plays a key role in apoptosis

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2
Q

Describe the outer membrane of mitochondria

A

-perforated with large channels (porins)
-allow entry of molecules < 5000 kDa
-contains enzymes involved in mitochondrial lipid synthesis

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3
Q

Describe the mitochondrial intermembrane space

A

-contains enzymes that use ATP to phosphorylate other nucleotides
-H+ pumped into this space to create proton grad to drive oxidative phosphorylation - impermeable to H+

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4
Q

Describe the inner membrane of mitochondria

A

-folded into cristae to maximise SA
-contains redox performing proteins of electron transport chain
-proteins for ATP synthesis
-transport proteins to move molecules in + out of matrix

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5
Q

Describe the mitochondrial matrix

A

-internal space containing enzymes of Krebs cycle
-contains: mitochondrial DNA, ribosomes, tRNAs, enzymes, metabolites

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6
Q

Do mitochondria contain their own genetic material?

A

-yes
-circular, double stranded chromosome
-DNA inherited from the mother

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7
Q

What are mitochondria always in a dynamic flux between?

A

Fusion and fission

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8
Q

What is quality controlled fission?

A

-mitochondria segregate debris to 1 side + undergo fission
-half without debris carries on as mitochondria
-half with debris undergoes mitophagy - destroyed by autophagosome

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9
Q

What are the translocator proteins embedded in the membranes of mitochondria?

A

-TOM complex - translocator of outer membrane
-SAM complex - sorting + assembling machinery
-TIM complex - translocator of inner membrane
-OXA complex - cytochrome oxidase activity

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10
Q

Describe how proteins enter the mitochondria

A

-precursor protein with signal sequence binds to receptors in TOM complex
-they’re then inserted into TIM23 complex, then pushed through into the matrix
-signal peptidase cleaves signal sequence off
-leaves mature mitochondrial protein in matrix

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11
Q

Are mitochondrial precursor proteins folded or unfolded?

A

Unfolded

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12
Q

What can the mitochondrial precursor proteins do before docking and how can this be stopped?

A

-fold before docking with TOM complex
-can be stopped by binding interacting proteins to the newly synthesised polypeptide chain e.g chaperones

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13
Q

What do chaperones need energy for?

A

To dissociate the chaperones from the polypeptide chain

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14
Q

What happens because the TOM complex can’t insert proteins into the bilayer?

A

Enter in intermembrane space + kept unfolded by chaperones

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15
Q

What is the most common route for proteins entering the inner mitochondrial membrane?

A

Use TOM + TIM 23 complex

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16
Q

What is the alternate route for proteins entering the inner mitochondrial membrane?

A

-protein completely enters the matrix
-signal sequence cleavage unmasks a 2nd signal
-signal causes insertion int OXA complex

17
Q

What are multipass IMM proteins and what do they allow chaperones to do?

A

-they snake through TOM as a loop
-allow chaperones to bind to stop folding + guide towards TIM22

18
Q

Describe peroxisomes

A

-only have a single membrane
-don’t contain DNA or ribosomes
-contain oxidative enzymes

19
Q

What is the function of peroxisomes?

A

-carry out oxidative reactions
-remove H atoms from organic compounds
to produce H2O2
-H2O2 used by peroxidases in other reactions
-also involved in b-oxidation of fatty acids

20
Q

What are the equations for the 2 reactions carried out in peroxisomes?

A
  1. RH2 + O2 –> R + H2O2
  2. H2O2 + R’H2 –> R’ + 2H2O
21
Q

Why must the 2 reactions in peroxisomes be done together?

A

To prevent H2O2 from remaining in the body

22
Q

Where are most peroxisomal proteins made?

A

-made in cytosol
-inserted into membrane of pre-existing peroxisomes

23
Q

How do new peroxisomes arise?

A

From pre-existing ones by organelle growth + fission

24
Q

How do proteins get into peroxisomes?

A

-Pex5 recognises signal sequence + accompanies cargo into peroxisome
-Pex5 then ubiquitylated + cycled back to cytosol

25
Q

What does a mutation in Pex5 cause?

A

-Zellweger syndrome
-severe brain, liver + kidney abnormalities