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Foundations 1 > Oxidative Phosphorylation > Flashcards

Oxidative Phosphorylation Flashcards

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1
Q

Mitochondrial membrane structure

A
  • outer membrane (very impermeable)
  • intermembrane space
  • inner membrane
  • matrix
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2
Q

What is the structure of the mitochondrial genome?

A

Circular (no chromatin, histones, etc)

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3
Q

What are the contents of the mitochondrial genome?

A

~17kb = 37 genes (13 proteins, 22 tRNAs, 2 rRNAs)

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4
Q

Describe the structure of a voltage dependent anion channel.

A

B barrel with a-helix that opens/closes the channel in a voltage dependent manner

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5
Q

Where are voltage dependent anion channels located and what do they transport?

A
  • Outer mitochondrial membrane

- ATP/ADP, Pi, pyruvate, citrate

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6
Q

What are some inner membrane transporters and what are their substrates?

A
  • Adenine Nucleotide Transporter = ATP/ADP
  • Dicarboxylate carrier = malate/phosphate
  • Tricarboxylate carrier = citrate + H+/malate
  • Pyruvate carrier = OH-/pyruvate
  • Phosphate carrier = OH-/phosphate
  • Ornithine transporter = ornithine/citrulline
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7
Q

What key reactants/products are transported in/out of the mitochondria for oxidative phosphorylation?

A

IN: O2, ADP, food-derived pyruvate and FAs
OUT: CO2, ATP

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8
Q

What is the purpose of the glycerol-3-phosphate shuttle?

A

Regenerate oxidized NAD+ for glycolysis

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9
Q

What reaction is catalyzed by cytosolic glycerol-3-P DH?

A
  • Reduces DHAP to glycerol-3-P, requiring 1 NADH

- Regenerates oxidized NAD+ for glycolysis

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10
Q

What reaction is catalyzed by mitochondrial glycerol-3-P DH?

A
  • Glycerol-3-P is oxidized back to DHAP, generating 1 FADH

- Protein is inner-membrane bound: DHAP remains in cytosol and electrons from FADH are transferred to the ETC

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11
Q

What are the major and minor pathways for transporting re-oxidizing the NADH generated in glycolysis to NAD+?

A

Major: G3P shuttle
Minor: malate-aspartate shuttle

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12
Q

What is the purpose of the malate-aspartate shuttle?

A

Regenerate oxidized NAD+ for glycolysis

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13
Q

What are the steps of the malate-aspartate shuttle?

A

Overall: transport + carbon skeleton recycling

  1. cytosolic OAA reduced to malate, requiring 1 NADH (and regenerating an NAD+ for glycolysis)
  2. Malate transport across inner mitochondrial membrane
  3. Malate oxidized to OAA, generating 1 NADH (goes into ETC)
  4. OAA is transaminated to aspartate, requiring glu and generating a-KG
  5. Aspartate is transported across the inner mitochondrial membrane to cytosol
  6. Aspartate transaminated to OAA, requiring a-KG and generating glu

*glu and a-KG transported across inner membrane

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14
Q

What is the function of complex 1?

A

NADH dehydrogenase:

  • accepts 2 electrons from NADH
  • electron transfer via FMN and Fe-S clusters to CoQ
  • 4 protons pumped into IM space
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15
Q

What is the function of complex 2?

A

Succinate dehydrogenase (TCA enzyme) + ETF CoQ oxidoreductase + G3PDH:

  • accepts electrons from succinate
  • electron transfer via FAD to CoQ
  • does not span membrane nor pump protons
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16
Q

What is the function of complex 3?

A

Cytb-c1 complex:

  • accepts electrons from reduced CoQ (CoQH2)
  • electron transfer via cyt b and Fe-S clusters to cyt c
  • cytochromes have a bound heme
  • pumps 4 protons across membrane
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17
Q

What is the function of complex 4?

A

Cyt c oxidase:

  • accepts electrons from cyt c
  • electron transfer via Cu and Fe ions and cyt a’s to O2
  • pumps 2 protons across membrane
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18
Q

What is ubiquinone?

A
  • Electron carrier that moves through the membrane to transport 2 protons and 2 electrons from complexes 1 and 2 to complex 3 in its reduced form
  • hydrophobic hydrocarbon tail is produced via cholesterol biosynthesis
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19
Q

What is cytochrome c?

A
  • Electron carrier that transports electrons from complex 3 to complex 4
  • Uses iron-sulfur clusters to complex electrons
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20
Q

What is the purpose of iron-sulfur clusters?

A
  • Coordinate electrons for transport
  • Heme holds iron
  • Proteins fold to expose free sulfhydrils on cysteines
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21
Q

How does redox potential change across the ETC?

Study These Flashcards
A
  • Redox potential (electron affinity) increases
22
Q

How does the energy per electron change across the ETC?

Study These Flashcards
A
  • Decreases slightly as some energy is lost as heat and also used at each step
23
Q

Why are protons pumped across the inner membrane?

Study These Flashcards
A

To create an electrochemical gradient: intermembrane space is + charged and acidic

24
Q

Which direction are protons pumped?

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A

matrix -> intermembrane space

25
What is the relationship between the cytoplasm and the intermembrane space?
Considered continuous because voltage gated channels allow for diffusion
26
What is the chemiosmotic theory of oxidative phosphorylation?
- A proton motive force is generated from the electrochemical proton gradient established across the inner membrane - Protons want to move from the positively charged, acidic inner membrane space down the gradient into the matrix
27
What is the purpose of F0F1 ATP synthase?
- Transfers chemical energy (protons) into mechanical energy (rotor) back to chemical energy (ATP) - As protons move down the gradient through the rotor, conformational changes to the protein allow for generation of ATP
28
Why is ATP synthase reversible?
- Can hydrolyze ATP to pump protons into the inter membrane space - Allows electrochemical gradient/membrane potential to be maintained for other processes (other than ATP synthesis) while the cell is in a high energy state and no ATP synthesis is needed (ie ETC is inactive)
29
How is the rate of oxygen consumption by complex 4 controlled?
ADP concentration
30
What is oligomycin?
ETC inhibitor that blocks the F0 channel of ATP synthase?
31
What are some inhibitors of of CoQ reduction?
via complex 1: piericidin A, amobarbital, rotenone | via complex 2: carboxin, TTFA
32
What are some inhibitors of complexes 2, 3, and 4?
2: malonate 3: BAL, antimycin A 4: H2S, CO, CN-
33
How do ETC uncouplers work?
- Facilitate transport of protons across inner membrane, dissipating the gradient - Heat is generated instead of ATP
34
thermogenin
- ETC uncoupling protein - found in inner mitochondrial membrane in brown fat in infants - transports protons back into the matrix after they are transported into the inner membrane space via the etc to produce heat
35
2,4-DNP
- chemical etc uncoupler - small hydrophobic molecule binds proton in the acidic IM space and diffuses across the membrane to the matrix - used as a weight loss drug as FAs could be burned w/o ATP generation
36
What are other functions of the electrochemical gradient?
- Voltage gradient: drives transport of ADP (-3) into the matrix and ATP (-4) into the IM space/cytosol - pH gradient: phosphate (-) and pyruvate (-) import
37
What does it mean that the mitochondria is a calcium sink?
Takes in and releases Ca2+ ions to maintain cytosolic [Ca2+]
38
What is the function of the mitochondrial permeability transition pore?
- Allows free passage of water and solutes into the mitochondria => lysis - Involved in apoptosis
39
What are the components of the mitochondrial permeability transition pore?
- ANT in inner membrane + VDAC in outer membrane - CK in IM space to accept ATP - HK in cytosol to accept ATP
40
What regulates mitochondrial permeability transition pore formation?
+ : atractyloside, Ca2+, Bax, PO4, ROS | - : bongkrekic acid, ATP
41
What reactions generate ROS?
- Fenton reaction: H2O2 + iron => hydroxyl ion + hydroxyl radical - O2 + electron => superoxide (ROS) - superoxide + electron + 2 protons => H2O2 which can combine with a proton and an electron to make water and a hydroxyl radical
42
Why is it dangerous to have free iron in the cell?
- Can generate hydroxyl radicals by reducing H2O2 | - This is why we need heme, ferritin
43
What are some NOS's?
- nitric oxide = free radical - peroxynitrite = strong oxidizing agent - peroxynitrous acid - nitronium ion = nitrating agent - nitrogen dioxide = free radical - nitrogen trioxide = nitrosating agent
44
What are some sources of NOS's?
- Nitric oxide synthase generates nitric oxide with conversion of arginine to citrulline - Diet and gut bacteria generate nitrite which can be converted to nitrogen trioxide
45
What are some non-enzymatic antioxidants?
- vitamins C and E - carotenoids (dietary) - flavonoids (dietary) - uric acid (purine catabolism) - melatonin
46
What antioxidant enzymes defend against oxygen radicals?
- superoxide dismutase (cytosol and mitochondria) converts 2 superoxide into O2 + H2O2 - catalase (peroxisome) converts 2 H2O2 into 2 H2O + O2 - glutathione peroxidase reduces H2O2 to H2O with the oxidation of 2 GSH
47
What is glutathione?
- GSH = gly + cys + glu | - the free sulfhydryls on the cys residues of 2 GSH will form a disulfide bond that can be used as a reducing agent
48
How is reduced 2 GSH regenerated from GSSG?
Glutathione reductase reduces GSSG using NADPH
49
What cellular damage is caused by ROS?
- Protein damage => aggregation - DNA damage => apoptosis, cancer - Membrane lipid peroxidation => "contagious" as damaged lipids act as free radicals too => change in membrane permeability - Membrane damage => Ca2+, Na+, and water influx => cell swelling
50
Generally, how are ROS and NOS generated?
oxidative metabolism

Foundations 1 (26 decks)

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