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Foundations 1 > Oxidative Phosphorylation > Flashcards

Oxidative Phosphorylation Flashcards

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?

A
  • Redox potential (electron affinity) increases
22
Q

How does the energy per electron change across the ETC?

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?

A

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

24
Q

Which direction are protons pumped?

A

matrix -> intermembrane space

25
Q

What is the relationship between the cytoplasm and the intermembrane space?

A

Considered continuous because voltage gated channels allow for diffusion

26
Q

What is the chemiosmotic theory of oxidative phosphorylation?

A
  • 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
Q

What is the purpose of F0F1 ATP synthase?

A
  • 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
Q

Why is ATP synthase reversible?

A
  • 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
Q

How is the rate of oxygen consumption by complex 4 controlled?

A

ADP concentration

30
Q

What is oligomycin?

A

ETC inhibitor that blocks the F0 channel of ATP synthase?

31
Q

What are some inhibitors of of CoQ reduction?

A

via complex 1: piericidin A, amobarbital, rotenone

via complex 2: carboxin, TTFA

32
Q

What are some inhibitors of complexes 2, 3, and 4?

A

2: malonate
3: BAL, antimycin A
4: H2S, CO, CN-

33
Q

How do ETC uncouplers work?

A
  • Facilitate transport of protons across inner membrane, dissipating the gradient
  • Heat is generated instead of ATP
34
Q

thermogenin

A
  • 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
Q

2,4-DNP

A
  • 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
Q

What are other functions of the electrochemical gradient?

A
  • 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
Q

What does it mean that the mitochondria is a calcium sink?

A

Takes in and releases Ca2+ ions to maintain cytosolic [Ca2+]

38
Q

What is the function of the mitochondrial permeability transition pore?

A
  • Allows free passage of water and solutes into the mitochondria => lysis
  • Involved in apoptosis
39
Q

What are the components of the mitochondrial permeability transition pore?

A
  • ANT in inner membrane + VDAC in outer membrane
  • CK in IM space to accept ATP
  • HK in cytosol to accept ATP
40
Q

What regulates mitochondrial permeability transition pore formation?

A

+ : atractyloside, Ca2+, Bax, PO4, ROS

- : bongkrekic acid, ATP

41
Q

What reactions generate ROS?

A
  • 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
Q

Why is it dangerous to have free iron in the cell?

A
  • Can generate hydroxyl radicals by reducing H2O2

- This is why we need heme, ferritin

43
Q

What are some NOS’s?

A
  • nitric oxide = free radical
  • peroxynitrite = strong oxidizing agent
  • peroxynitrous acid
  • nitronium ion = nitrating agent
  • nitrogen dioxide = free radical
  • nitrogen trioxide = nitrosating agent
44
Q

What are some sources of NOS’s?

A
  • 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
Q

What are some non-enzymatic antioxidants?

A
  • vitamins C and E
  • carotenoids (dietary)
  • flavonoids (dietary)
  • uric acid (purine catabolism)
  • melatonin
46
Q

What antioxidant enzymes defend against oxygen radicals?

A
  • 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
Q

What is glutathione?

A
  • 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
Q

How is reduced 2 GSH regenerated from GSSG?

A

Glutathione reductase reduces GSSG using NADPH

49
Q

What cellular damage is caused by ROS?

A
  • 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
Q

Generally, how are ROS and NOS generated?

A

oxidative metabolism

Foundations 1 (26 decks)

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