Electron Transport Chain Flashcards
Summarise the electron transport chain (ETC)
The electron transport chain is made up of 4 protein complexes that couple redox reactions, creating an electrochemical gradient that leads to the creation of ATP in a complete system named oxidative phosphorylation. It occurs in mitochondria in both cellular respiration and photosynthesis. The electrons come from breaking down organic molecules, and energy is released. The electrons enter the chain after being excited by light, and the energy released is used to build carbohydrates.
What processes are involved in aerobic cellular respiration?
- Glycolysis
- The citric acid cycle (Krebs Cycle)
- Oxidative phosphorylation
What is the process of Glycolysis?
Glucose metabolises into 2 molecules of pyruvate, with an output of ATP and nicotinamide adenine dinucleotide (NADH). Each pyruvate oxidises into Acetyl CoA and an additional molecule of NADH and carbon dioxide. The Acetyl CoA is then used in the Krebs cycle.
What is the process of the Krebs cycle?
The Krebs cycle is a chain of chemical reactions that produce CO2, NADH, flavin adenine dinucleotide (FADH2) and ATP. In the final step of the cycle, the three NADH and one FADH2 amassed from the previous steps are used in oxidative phosphorylation, to make water and ATP.
What are the 2 parts of oxidative phosphorylation?
- The electron transport chain (ETC)
- Chemiosmosis
How does the ETC produce energy?
The ETC is a collection of proteins bound to the inner mitochondrial membrane and organic molecules, which electrons pass through a series of redox reactions and release energy.
What does the energy released from the ETC form?
The energy released forms a proton gradient, which is used in chemiosmosis to make large amounts of ATP by the protein ATP-synthesis.
Summarise ETC & photosynthesis
Photosynthesis is a metabolic process that converts light energy into chemical energy to build sugars. In the light-dependent reactions, light energy and water are used to make ATP, NADH and oxygen. The proton gradient used to make the ATP forms via an ETC. in the light-independent reactions, sugar is made from the ATP and NADPH from previous reactions.
Summarise the ETC at a cellular level
In the ETC, the electrons go through a chain of proteins that increases its reduction potential and causes a release in energy. Most of this energy is dissipated as heat or used to pump hydrogen ions (H+) from the mitochondrial matrix to the inter membrane space and create a proton gradient. This gradient increases the acidity in the inter-membrane space and creates an electrical difference with a positive charge outside and a negative charge inside.
What is the order of ETC proteins?
The ETC proteins in a general order are:
Complex I
Complex II
Coenzyme Q
Complex III
Cytochrome C
Complex IV
What is complex I also known as?
Ubiquinone oxidoreductase
What is complex 1 made up of?
It is made up of:
NADH dehydrogenase
Flavin mononucleotide (FMN)
Eight iron-soulful (Fe-S) clusters
What happens at complex I?
The NADH donated from glycolysis and the citric acid cycle is oxidised here, transferring 2 electrons from NADH to FMN. Then they are transferred to the Fe-S clusters and finally from Fe-S to coenzyme Q.
How does the process at complex I contribute to the electrochemical gradient?
4 hydrogen ions pass from the mitochondrial matrix to the inter-membrane space.
What is complex II also know as?
Succinate dehydrogenase
What happens in complex II?
Complex II accepts succinate (an intermediate in the critic acid cycle) and acts as a second entry point to the ETC.
What is less ATP produced in the complex II pathway?
When succinate oxidises to fumarate, 2 electrons are accepted by FAD within complex II. FAD passes them to Fe-S clusters and then to coenzyme Q, like complex I. No proteins are translocated across the membrane by complex II, therefore producing less ATP in this pathway/
What is coenzyme Q also known as?
Ubiquinone
What is coenzyme Q made up of?
It is made up of quinone and a hydrophobic tail
What is coenzyme Q purpose?
It’s purpose is to function as an electron carrier and transfer electrons to complex III. Coenzyme Q also undergoes reduction to semi quinone (partially reduced, radical form CoQH-) and Ubiquinone (fully reduced CoQH2) through the Q cycle.
What is complex III also know as?
Cytochrome c reductase
What is complex III made up of?
It is made up of cytochrome b, Rieske subunits (containing 2 Fe-S clusters) and cytochrome c proteins.
What is a cytochrome?
It is a protein involved in electron transfer that contains a heme group.
What happens to heme groups during the electron transfers?
The heme groups alternate between ferrous (Fe+) and ferric (Fe3+) states during the electron transfer.
What is complex IV also know as?
Cytochrome c oxidise
What does complex IV do?
It oxidises cytochrome c and transfers the electrons to oxygen, the final electron carrier in aerobic cellular respiration.
How does complex IV produce molecules of water?
The cytochrome proteins a and a3, in addition to heme and copper groups in complex IV transfer the donated electrons to the bound deoxygenated species, converting it into molecules of water.
What happens to the free energy in complex IV?
The free energy from the electron transfer causes 4 protons to move into the inter-membrane space contributing to the proton gradient.
Oxygen reduces via the following reaction:
2 cytochrome c(red) + 1/2O2 +4H+(matrix) -> 2 cytochrome c(ox) + 1H2O + 2H+(inter-membrane)
What inhibits complex I (coenzyme Q binding site)?
Rotenone (and some barbiturates)
What inhibits complex II (coenzyme Q binding site)
Carboxin
What theoretically inhibits coenzyme Q?
Doxorubicin
What inhibits complex III (cytochrome c reductase)?
Antimycin A
What inhibits IV (cytochrome c oxidase)?
Carbon monoxide
Cyanide
What inhibits ATP synthase (complex V)?
Oligomycin
