Oxidative Phosphorylation Flashcards

Flashcards covering oxidative phosphorylation, electron transport chain complexes, shuttles, ATP synthesis mechanism, reactive oxygen species, inhibitors, uncouplers, and mitochondrial genetic defects.

What are the two main phases of energy production from fuel oxidation?

Phase 1 is the production of reduced $\text{NADH}$ and $\text{FADH}_2$, and Phase 2 is the use of generated energy to produce $\text{ATP}$ via oxidative phosphorylation.

Why can cytosolic $\text{NADH}$ not directly enter the mitochondrial matrix for oxidative phosphorylation?

The inner mitochondrial membrane (IMM) lacks an $\text{NADH}$ transporter.

How does the Glycerol 3-phosphate shuttle transfer reducing equivalents into the mitochondria?

Electrons are transferred from $\text{NADH}$ to dihydroxyacetone phosphate (DHAP) by cytosolic glycerol 3-phosphate dehydrogenase to form glycerol 3-phosphate. Glycerol 3-phosphate is then oxidized by the mitochondrial isoenzyme, reducing $\text{FAD}$ to $\text{FADH}_2$.

How does the Malate shuttle transport reducing equivalents across the inner mitochondrial membrane?

Oxaloacetate is reduced to malate in the cytosol using $\text{NADH}$. Malate enters the mitochondria and is oxidized back to oxaloacetate, reforming $\text{NADH}$.

What are the functions of the adenine nucleotide antiporter and the phosphate transporter in $\text{ATP}$ synthesis?

The adenine nucleotide antiporter imports $1\,\text{ADP}$ from the cytosol into the matrix while exporting $1\,\text{ATP}$ into the cytosol. The phosphate transporter carries phosphate from the cytosol into the matrix.

What structural components make up the mitochondrial electron transport chain (ETC)?

The ETC consists of four large multiprotein complexes (Complexes I–IV) and two small mobile carriers: coenzyme Q ($\text{CoQ}$) and cytochrome c.

Which prosthetic groups are associated with each complex of the electron transport chain?

Complexes I & II contain $\text{FAD}$ and $\text{FMN}$; Complexes III & IV contain heme groups; Complex IV also contains copper ions ($\text{Cu}$).

What is the systematic name of Complex I, and how many protons does it pump per $\text{NADH}$ oxidized?

Complex I is $\text{NADH:CoQ}$ oxidoreductase (dehydrogenase). Energy lost during electron transfer is used to pump $4\,\text{H}^+$ from the matrix into the intermembrane space (IMS).

What reaction is catalyzed by Complex II (succinate dehydrogenase), and how many protons does it pump?

Complex II oxidizes succinate to fumarate in the TCA cycle with the reduction of $\text{FAD}$ to $\text{FADH}_2$. It passes electrons one at a time to $\text{CoQ}$ and pumps $0\,\text{H}^+$ (no protons) across the membrane.

What are the three oxidation states of Coenzyme Q (ubiquinone) shown in this structural pathway?

Ubiquinone ($\text{Q}$, fully oxidized), Semiquinone radical ($^\bullet\text{QH}$), and Ubiquinol ($\text{QH}_2$, fully reduced).

What is the path of electron flow through Complex III (cytochrome $bc_1$), and how many protons are pumped?

Electrons flow from ubiquinone $\rightarrow$ cytochrome b $\rightarrow$ cytochrome $c_1$ $\rightarrow$ cytochrome c. A high drop in energy during electron movement drives the pumping of $4\,\text{H}^+$ into the IMS.

How does Complex IV (cytochrome oxidase) reduce oxygen to water, and how many protons are pumped?

Complex IV conducts electrons through cytochromes a and $a_3$. When 4 electrons are available, 4 protons from the matrix reduce and split $\text{O}_2$ to form $2\,\text{H}_2\text{O}$, pumping $2\,\text{H}^+$ per $\text{H}_2\text{O}$ formed (or $2\,\text{H}^+$ per oxygen reduction event) into the IMS.

What are the four sequential steps involved in the progressive reduction of oxygen to water?

Step 1: $\text{O}_2 + e^- \rightarrow \text{O}_2^{\bullet-}$ (Superoxide); Step 2: $\text{O}_2^{\bullet-} + e^- + 2\,\text{H}^+ \rightarrow \text{H}_2\text{O}_2$ (Hydrogen peroxide); Step 3: $\text{H}_2\text{O}_2 + e^- + \text{H}^+ \rightarrow \text{H}_2\text{O} + \text{OH}^\bullet$ (Hydroxyl radical); Step 4: $\text{OH}^\bullet + e^- + \text{H}^+ \rightarrow \text{H}_2\text{O}$.

What cellular damage is caused by oxidative stress resulting from reactive oxygen species (ROS)?

ROS accumulation causes lipid peroxidation, protein oxidation and degradation or aggregation, and DNA damage (base oxidation or double-strand breaks).

Which specific enzymes and antioxidants serve as cellular defenses against oxygen toxicity?

Enzymes include glutathione peroxidase, catalase, and superoxide dismutase. Antioxidants include Vitamin A, Vitamin C, and Vitamin E.

According to this diagram, which specific inhibitors block electron transfer at Complex I, Complex III, and Complex IV?

Complex I is blocked by Amytal and Rotenone; Complex III is blocked by Antimycin A; Complex IV is blocked by $\text{CN}^-$, $\text{CO}$, $\text{H}_2\text{S}$, and $\text{NaN}_3$.

What is the key concept of Mitchell's chemiosmotic theory regarding ATP synthesis?

The energy needed to phosphorylate $\text{ADP}$ to $\text{ATP}$ is provided by a flow of protons moving down an electrochemical gradient established by $\text{H}^+$ pumped from the matrix into the IMS during electron transport.

Based on the structure of ATP synthase shown, what are the primary features and functions of the $F_1$ and $F_o$ domains?

The $F_1$ domain is located in the mitochondrial matrix and contains catalytic activity (head composed of 3 $\alpha\beta$-subunits). The $F_o$ domain is embedded in the inner mitochondrial membrane and contains the rotor and $\text{H}^+$ channel.

How many ATP molecules are produced by one complete c ring rotation of ATP synthase?

One complete c ring rotation produces 3 molecules of $\text{ATP}$.

What is the mechanism of action of oligomycin on ATP synthase?

Oligomycin binds to the $F_o$ domain of $\text{ATP}$ synthase, closing the $\text{H}^+$ channels and preventing the reentry of $\text{H}^+$ into the matrix, which inhibits $\text{ATP}$ synthesis and blocks oxidative phosphorylation.

How do uncoupling proteins and 2,4-dinitrophenol (DNP) affect oxidative phosphorylation?

Uncoupling proteins form channels and DNP acts as a lipophilic $\text{H}^+$ carrier, allowing protons to reenter the matrix without passing through $\text{ATP}$ synthase. This decreases $\text{ATP}$ production, increases $\text{O}_2$ consumption and ETC rate, and releases energy as heat.

What biological function is mediated by UCP1 (thermogenin)?

UCP1 (thermogenin) is responsible for heat production via non-shivering thermogenesis in mitochondria-rich brown adipose tissue.

What five requirements are necessary for normal oxidative phosphorylation to occur?

1. Electron donors ($\text{NADH}$, $\text{FADH}_2$); 2. Electron acceptor ($\text{O}_2$); 3. Intact mitochondrial membrane; 4. Functional ETC components; 5. $\text{ATP}$ synthase.

Why do genetic mutations in mtDNA disproportionately cause oxidative phosphorylation defects, and what are two examples?

mtDNA has a mutation rate 10x greater than nuclear DNA and encodes 13 proteins involved in oxidative phosphorylation. Examples include Leber's hereditary optic neuropathy (Complex I defect) and Leigh syndrome ($F_o$ defect).