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PSA712 Biochemistry > Mitochondria/Oxidative Phosphorylation > Flashcards

Mitochondria/Oxidative Phosphorylation Flashcards

1
Q

Describe the process of endosymbiosis.

A
  1. Prokaryote cell grows and evolves to form eukaryote.
  2. Plasma membrane forms infoldings and pinches parts to form membranes around organelles.
  3. Cell by chance engulfs aerobic bacterium.
  4. Formation of a eukaryote cell (aerobic bacterium -> mitochondria).
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2
Q

What are the consequences of mitochondria once being their own cells (aerobic bacterium)?

A

They have their own:

  1. Genome
  2. Biosynthetic machinery for making RNA and proteins.
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3
Q

How many genes are found in the mitochondria genome and what do they consist of?

A

37 genes in total:
2 rRNA
22 tRNA
12 protein-coding genes

There is also non-coding DNA.

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4
Q

During fertilisation, male mitochondria that are present in the fertilised egg are degraded. What does this mean?

A

All mitochondria in our bodies originate from our mothers.

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5
Q

Define fusion regarding mitochondria.

A

2 mitochondria come together to form a larger one.

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6
Q

Define fission regarding mitochondria.

A

Large mitochondria break down into two organelles.

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7
Q

Fission and fusion can have what effect on mitochondrial DNA (mtDNA) copies.

A

Increase/decrease.

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8
Q

When mtDNA is replicated, is it in synchrony with fission events or random?

A

Random.

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9
Q

Prior to fission, what happens to mtDNA?

A

mtDNA localise to the opposite poles to ensure they are incorporated into the new mitochondria during division.

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10
Q

What is mitochondrial biogenesis?

A

The increase in abundance of mitochondrial proteins, mtDNA and mitochondrial number.

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11
Q

Mitochondrial ribosomes are 55S. How is this divided between the large and small subunits?

A

39S = 16S rRNA and 50 proteins.

28S = 12S rRNA and 30 proteins.

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12
Q

The 55S refers to the size of a mitochondrial ribosome. What does the S stand for?

A

Svedberg unit.

The larger the number, the bigger the molecule/subunit.

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13
Q

What are the two translocases used in the process of making mitochondrial proteins?

A 
TIM = translocase of the inner membrane 
TOM = translocase of the outer membrane
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14
Q

Describe the process of transporting mitochondrial proteins.

A
  1. Protein is escorted to mitochondria from the ribosome by chaperones.
  2. Signal sequence is recognised by a protein in the outer membrane (TOM).
  3. Binding of signal sequence pulls protein into mitochondria.
  4. Signal sequence is recognised by TIM.
  5. Both translocases pull the entire protein into the matrix.
  6. Protein reaches matrix and folds into its 3D structure.
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15
Q

What is the role of peptidases once a mitochondrial protein has entered the mitochondria via TOM and TIM?

A

Peptidases chop off the signal sequence, leaving the mature protein.

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16
Q

How is pyruvate transported into the mitochondria to be converted into acetyl CoA?

A
  1. Pyruvate is transported through porins in the outer membrane.
  2. Pyruvate passes into the matrix via mitochondrial pyruvate carriers.
  3. In the matrix, pyruvate is decarboxylated to form acetyl CoA.
17
Q

How are fatty acids transported into the mitochondria?

A
  1. FA is transported into cytosol and converted to fatty acyl-coA.
  2. Fatty acyl CoA + carnitine form acyl-carnitine.
  3. Acyl-carnitine crosses outer membrane to inter-membrane space.
  4. Acyl-carnitine translocase enables acyl-carnitine to move into matrix.
  5. Acyl-carnitine seperates and carnitine passes back to cytosol.
  6. Leaves acyl CoA in matrix to enter beta oxidation.
18
Q

What catalyses the reaction between fatty acyl-coA and carnitine to form acyl-carnitine?

A

CPTI = Carnitine Palmitoyl Transferase I

19
Q

What catalyses the reaction to seperate acyl-carnitine into acetyl coA and carnitine?

A

CPTII = Carnitine Palmitoyl Transferase II

20
Q

What is the process called which transports NADH into the mitochondria from glycolysis?

A

Malate Aspartate Shuttle.

21
Q

Describe what happens in the malate aspartate shuttle (refer to NADH).

A
  1. NADH (from glycolysis) is oxidised in the cytosol and passes its electrons to oxaloacetate -> malate.
  2. Malate passes through anti-porter crossing the inner membrane, into the matrix.
  3. Alpha-ketogluterate moves from matrix to cytosol via anti-porter at the same time.
  4. Malate is oxidised to for oxaloacetate and NAD is reduced to NADH.
22
Q

What happens during the electron transport chain (ETC) and oxidative phosphorylation?

A
  1. Electrons, carried by NADH and FADH2 are passed into ETC and accepted by electron carriers (metal ions).
  2. Electrons lose energy as they are passed down the chain.
  3. Energy is used to pump H+ ions cross the inner mitochondrial membrane (matrix -> inner mitochondrial space).
  4. Electrons are passed to oxygen to form water.
23
Q

What happens at Complex I (NADH-CoQ reductase) in oxidative phosphorylation?

A
  1. NADH transfers its electrons into complex I and NAD+ is recycled.
  2. Electrons accepted by iron-sulphur clusters.
  3. 2H+ reduce CoQ to form CoQH2.
  4. The energy released is used to pump 4H+ across the membrane into intermembrane space.
NADH = 4
FADH2 = N/A
24
Q

What happens at Complex II in oxidative phosphorylation?

A
  1. Oxidation of succinate -> fumarate.
  2. FADH2 is coupled in succinate dehydrogenase and then immediately passed into complex II to Fe-S clusters.
    Electrons passed to CoQ along with 2H+ to form CoQH2.
  3. No enough energy is produced to pump H+ across membrane.
NADH = N/A
FADH2 = 0
25
Q

What happens at Complex III in oxidative phosphorylation?

A
  1. CoQH2 from Complex I/II donates electrons to Fe-S clusters and cytochoromes.
  2. 2H+ released into intermembrane space.
  3. Electrons passed to cytochrome C -> forms 2 reduced cytochrome C molecules.
  4. Energy released from this pumps 2 more H+ into intermembrane space.
NADH = 4
FADH2 = 4
26
Q

What happens at Complex IV in oxidative phosphorylation?

A
  1. Electrons carried by cytochrome C molecules are donated to complex.
  2. Oxygen accepts two 2 electrons to form 1/2O2 + 2H+ = H20.
  3. Energy released via REDOX reactions pump 2H+ molecules across the inter-membrane space.

Per molecule of NADH as we can’t have 1/2O2:
NADH = 2
FADH2 = 2

27
Q

As we cannot have 1/2O2 in complex IV, what happens?

A
  1. Complex IV clings onto protons.
  2. When 4 electrons have been collected, they are passed onto an O2 molecule.

O2 + 4H+ = 2H2O

28
Q

The pH difference across the inner membrane in a mitochondrial produces what gradient?

A

Electrochemical proton gradient.

29
Q

What happens to ATP synthase during oxidative phosphorylation?

A
  1. Protons enter ATP synthase through the F0 region.
  2. Protons move through the subunits of F0, causing them to rotate.
  3. The shaft rotates.
  4. F1 does not rotate.
  5. ADP and Pi bind to specific sites.
  6. When the shaft rotates, it causes a conformational change in the F1 region and catalyses the formation of ATP.

PSA712 Biochemistry (11 decks)

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