- 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

Oxidative Phosphorylation Flashcards by Emma Office

Mitochondrial membrane structure

outer membrane (very impermeable)
intermembrane space
inner membrane
matrix

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What is the structure of the mitochondrial genome?

Circular (no chromatin, histones, etc)

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What are the contents of the mitochondrial genome?

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

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Describe the structure of a voltage dependent anion channel.

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

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

Outer mitochondrial membrane

- ATP/ADP, Pi, pyruvate, citrate

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

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

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

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

Regenerate oxidized NAD+ for glycolysis

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

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

- Regenerates oxidized NAD+ for glycolysis

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

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

Major: G3P shuttle
Minor: malate-aspartate shuttle

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What is the purpose of the malate-aspartate shuttle?

Regenerate oxidized NAD+ for glycolysis

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What are the steps of the malate-aspartate shuttle?

Overall: transport + carbon skeleton recycling

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

*glu and a-KG transported across inner membrane

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What is the function of complex 1?

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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What is the function of complex 2?

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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What is the function of complex 3?

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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What is the function of complex 4?

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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What is ubiquinone?

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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What is cytochrome c?

Electron carrier that transports electrons from complex 3 to complex 4
Uses iron-sulfur clusters to complex electrons

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What is the purpose of iron-sulfur clusters?

Coordinate electrons for transport
Heme holds iron
Proteins fold to expose free sulfhydrils on cysteines

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How does redox potential change across the ETC?

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Redox potential (electron affinity) increases

How does the energy per electron change across the ETC?

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Decreases slightly as some energy is lost as heat and also used at each step

Why are protons pumped across the inner membrane?

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

Which direction are protons pumped?

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matrix -> intermembrane space

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

Considered continuous because voltage gated channels allow for diffusion

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

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

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)

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

ADP concentration

What is oligomycin?

ETC inhibitor that blocks the F0 channel of ATP synthase?

What are some inhibitors of of CoQ reduction?

via complex 1: piericidin A, amobarbital, rotenone | via complex 2: carboxin, TTFA

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

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

How do ETC uncouplers work?

- Facilitate transport of protons across inner membrane, dissipating the gradient - Heat is generated instead of ATP

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

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

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

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

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

What is the function of the mitochondrial permeability transition pore?

- Allows free passage of water and solutes into the mitochondria => lysis - Involved in apoptosis

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

What regulates mitochondrial permeability transition pore formation?

+ : atractyloside, Ca2+, Bax, PO4, ROS | - : bongkrekic acid, ATP

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

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

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

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

What are some non-enzymatic antioxidants?

- vitamins C and E - carotenoids (dietary) - flavonoids (dietary) - uric acid (purine catabolism) - melatonin

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

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

How is reduced 2 GSH regenerated from GSSG?

Glutathione reductase reduces GSSG using NADPH

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

Generally, how are ROS and NOS generated?

oxidative metabolism

Oxidative Phosphorylation Flashcards

(50 cards)