Complex I

Definition

Complex I, also known as NADH-ubiquinone oxidoreductase, is the first enzyme complex in the electron transport chain that plays a critical role in cellular respiration. It catalyzes the transfer of electrons from NADH to ubiquinone (coenzyme Q), while simultaneously pumping protons from the mitochondrial matrix into the intermembrane space, contributing to the proton gradient essential for ATP synthesis. Its function is crucial in regulating electron transport and driving oxidative phosphorylation.

5 Must Know Facts For Your Next Test

1. Complex I is composed of multiple subunits and contains an iron-sulfur cluster, which facilitates electron transfer during its enzymatic reaction.
2. The process of electron transfer in Complex I results in the translocation of four protons across the mitochondrial membrane for each pair of electrons passed from NADH to ubiquinone.
3. Complex I plays a vital role in establishing the proton gradient required for ATP production, making it a key player in oxidative phosphorylation.
4. Mutations in genes encoding Complex I can lead to various mitochondrial disorders and have been linked to neurodegenerative diseases due to impaired energy production.
5. Inhibitors like rotenone can block Complex I's function, leading to a halt in the electron transport chain and subsequent effects on ATP synthesis and cellular metabolism.

Review Questions

• How does Complex I contribute to the establishment of the proton gradient necessary for ATP synthesis?
  • Complex I contributes to the proton gradient by actively transporting protons from the mitochondrial matrix into the intermembrane space during the transfer of electrons from NADH to ubiquinone. This process creates a higher concentration of protons outside the matrix than inside, generating potential energy that is harnessed by ATP synthase. The resulting proton motive force drives protons back into the matrix, powering ATP production.
• Discuss how Complex I is involved in regulating overall cellular respiration and its implications for metabolic health.
  • Complex I regulates cellular respiration by acting as a key entry point for electrons derived from NADH. It ensures that electrons are efficiently passed along the electron transport chain, promoting effective energy conversion. Disruptions in Complex I activity can lead to decreased ATP production and an increase in reactive oxygen species (ROS), which are associated with various metabolic disorders and contribute to aging and degenerative diseases.
• Evaluate the potential consequences of inhibiting Complex I with substances like rotenone on cellular metabolism and health.
  • Inhibiting Complex I with substances such as rotenone disrupts electron transfer in the mitochondrial respiratory chain, leading to decreased ATP synthesis and increased accumulation of NADH. This inhibition can severely impact cellular metabolism, resulting in reduced energy availability for cellular functions. Additionally, it causes an increase in reactive oxygen species, potentially leading to oxidative stress and damage that can contribute to conditions such as neurodegeneration and metabolic syndrome.

Related terms

NADH: Nicotinamide adenine dinucleotide (NADH) is a reduced coenzyme that carries electrons from metabolic processes to the electron transport chain, serving as a key electron donor.

Ubiquinone: Ubiquinone, also known as coenzyme Q, is a lipid-soluble molecule that transports electrons between Complex I (or II) and Complex III in the electron transport chain.

Proton Motive Force: The proton motive force is the electrochemical gradient generated by the difference in proton concentration across the inner mitochondrial membrane, driving ATP synthesis through ATP synthase.