Biochemistry Chapter 19

Oxidative Phosphorylation and Photophosphorylation

Chemiosmotic Theory

A theory proposed by Peter Mitchell that explains how ATP is generated in mitochondria and chloroplasts. It states that the energy from electron transport is used to pump protons across a membrane, creating a proton gradient that drives ATP synthesis.

Cristae

The folds of the inner mitochondrial membrane that increase its surface area, enhancing the capacity for ATP production.

Respiratory Chain

A series of protein complexes and other molecules embedded in the inner mitochondrial membrane that transfer electrons from electron donors to electron acceptors via redox reactions, coupled with the transfer of protons across the membrane.

Flavoprotein

Proteins that contain a nucleic acid derivative of riboflavin (vitamin B2), such as FAD or FMN, and are involved in redox reactions.

Reducing Equivalent

A term used to describe the transfer of one electron in redox reactions.

Ubiquinone (Coenzyme Q, Q)

A lipid-soluble electron carrier in the electron transport chain that transfers electrons between complexes I and III and between complexes II and III.

Cytochromes

Heme-containing proteins that play a key role in electron transport and redox reactions within the respiratory chain.

Iron-Sulfur Protein

Proteins that contain iron-sulfur clusters and are involved in electron transfer in the respiratory chain.

Rieske Iron-Sulfur Protein

A type of iron-sulfur protein found in complex III of the electron transport chain, characterized by a unique iron-sulfur cluster.

Complex I

Also known as NADH dehydrogenase, it is the first complex in the electron transport chain that transfers electrons from NADH to ubiquinone.

NADH Dehydrogenase

An enzyme that catalyzes the transfer of electrons from NADH to ubiquinone in the electron transport chain.

Vectorial

Referring to processes that involve the directional movement of molecules or ions across a membrane.

Complex II

Also known as succinate dehydrogenase, it is the second complex in the electron transport chain that transfers electrons from succinate to ubiquinone.

Succinate Dehydrogenase

An enzyme that catalyzes the oxidation of succinate to fumarate in the citric acid cycle and transfers electrons to the electron transport chain.

Reactive Oxygen Species (ROS)

Highly reactive molecules containing oxygen, such as superoxide radicals and hydrogen peroxide, that can damage cellular components.

Superoxide Radical

A type of reactive oxygen species formed by the one-electron reduction of oxygen, often produced in the electron transport chain.

Complex III

Also known as the cytochrome bc1 complex, it is the third complex in the electron transport chain that transfers electrons from ubiquinol to cytochrome c.

Cytochrome bc1 Complex

A protein complex in the electron transport chain that transfers electrons from ubiquinol to cytochrome c and pumps protons across the membrane.

Q Cycle

A mechanism in complex III of the electron transport chain that describes the transfer of electrons from ubiquinol to cytochrome c and the associated proton translocation.

Complex IV

Also known as cytochrome oxidase, it is the fourth complex in the electron transport chain that transfers electrons from cytochrome c to oxygen, forming water.

Cytochrome Oxidase

An enzyme in complex IV of the electron transport chain that catalyzes the reduction of oxygen to water.

Respirasome

A supercomplex of the electron transport chain that includes complexes I, III, and IV, facilitating efficient electron transfer and proton pumping.

Proton-Motive Force

The electrochemical gradient of protons across a membrane, generated by the electron transport chain, that drives ATP synthesis.

ATP Synthase

An enzyme that synthesizes ATP from ADP and inorganic phosphate using the energy from the proton-motive force.

F1 ATPase

The catalytic subunit of ATP synthase that synthesizes ATP.

C Ring

A ring of c subunits in the membrane-embedded part of ATP synthase that rotates during ATP synthesis.

Rotational Catalysis

The mechanism by which the rotation of the c ring in ATP synthase drives the synthesis of ATP.

Binding-Change Model

A model that describes how the rotation of ATP synthase leads to conformational changes in the enzyme, facilitating ATP synthesis.

P/O Ratio

The number of ATP molecules synthesized per oxygen atom reduced in the electron transport chain.

Malate-Aspartate Shuttle

A mechanism for transferring electrons from NADH in the cytosol to the mitochondria for use in the electron transport chain.

Glycerol 3-Phosphate Shuttle

A mechanism for transferring electrons from NADH in the cytosol to FADH2 in the mitochondria for use in the electron transport chain.

Acceptor Control

The regulation of the rate of oxidative phosphorylation by the availability of ADP.

Mass-Action Ratio (Q)

The ratio of the concentrations of products to reactants at any point in time during a reaction.

Brown Adipose Tissue (BAT)

A type of fat tissue that generates heat by burning calories, containing a high number of mitochondria.

Uncoupling Protein 1 (UCP1)

A protein in the inner mitochondrial membrane of brown adipose tissue that uncouples oxidative phosphorylation from ATP synthesis, generating heat.

Cytochrome P-450

A family of enzymes involved in the metabolism of drugs and the synthesis of cholesterol, steroids, and other lipids.

Xenobiotics

Chemical substances that are foreign to the biological system, including drugs and environmental pollutants.

Apoptosis

Programmed cell death, a regulated process that leads to the elimination of cells without releasing harmful substances into the surrounding area.

Apoptosome

A large protein complex that activates caspases, leading to apoptosis.

Caspase

A family of protease enzymes that play essential roles in apoptosis, necrosis, and inflammation.

Heteroplasmy

The presence of more than one type of mitochondrial DNA within a cell or individual.

Homoplasmy

The presence of only one type of mitochondrial DNA within a cell or individual.

Electron Transfer Chain Order

NADH → Q → cytochrome b → cytochrome c1 → cytochrome c → cytochrome a → cytochrome a3 → O2

Complex III Net Equation

QH₂ + 2cyt c + 2H⁺_N → Q + 2 cyt c + 2H⁺_P

Net Equation for 2 NADH

2NADH + 2H⁺ + O₂ → 2NAD⁺ + 2H₂O