Cytochromes are redox-active proteins containing a heme, with a central Fe atom at its core, as a cofactor. They are involved in electron transport chain and redox catalysis. They are classified according to the type of heme and its mode of binding.

Cytochrome, any of a group of hemoprotein cell components that, by readily undergoing reduction and oxidation (gain and loss of electrons) with the aid of enzymes, serve a vital function in the transfer of energy within cells. Hemoproteins are proteins linked to a nonprotein, iron-bearing component.

Cytochromes are proteins that contain heme as their prosthetic group and whose principal biological function, in the cells of animals, plants, and microorganisms, is electron transport.

A cytochrome is an enzyme that catalyzes redox reactions and is usually in the oxidoreductase enzyme class. The transfer electrons from reductant (one that causes something to gain electrons) to oxidant (one that causes something to lose electrons) using a heme at the active site.

Cytochrome c oxidase oxidizes cytochrome c and catalyzes the reduction of cytochrome c. Some bacteria are capable of aerobic respiration but have a different terminal oxidase system and give a negative result for the oxidase test.

Superoxide dismutase converts superoxide radicals to peroxide and oxygen (requires protons), and catalase converts hydrogen peroxide to water and oxygen. The reduction potential of iron from Fe3+ to Fe2+ is +0.77V.

In essence, the FINAL acceptor of the electrons at complex IV is oxygen (which forms water with the protons and electrons it accepts into its structure). This reduced FADH2 will transfer its electrons to mobile carrier Q.

Cytochrome c is a heme protein that is localized in the compartment between the inner and outer mitochondrial membranes where it functions to transfer electrons between complex III and complex IV of the respiratory chain.

The proton gradient produced by proton pumping during the electron transport chain is used to synthesize ATP. Protons flow down their concentration gradient into the matrix through the membrane protein ATP synthase, causing it to spin (like a water wheel) and catalyze conversion of ADP to ATP.

In metabolic control, the inner mitochondrial membrane must remain impermeable to protons. When this occurs, the electron transport won’t run unless oxidative phosphorylation is occurring and oxidative phosphorylation won’t occur unless there is a proton gradient.

The energy in the proton electrochemical gradient is used to make ATP. The coupling of the electrochemical gradient of H+ across the inner mitochondrial membrane with ATP synthesis is called chemiosmotic coupling (because there is a concentration difference across the membrane and an electric potential).

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The function of ATP synthase is to synthesize ATP from ADP and inorganic phosphate (Pi) in the F1 sector. This is possible due to energy derived from a gradient of protons which cross the inner mitochondrial membrane from the intermembrane space into the matrix through the Fo portion of the enzyme.

Phosphorylation. The PMF is the driving force for ATP synthesis by the mechanoenzyme complex V, or F1Fo ATPase. When protons flow through a channel in the enzyme, the movement spins the protein, much like wind drives a turbine.

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The three α-subunits and the three β-subunits are arranged alternately around a central α-helical coiled-coil in the γ-subunit. The γ-subunit protrudes from α3β3-subcomplex and the δ- and ε-subunits are associated with its foot. The foot interacts with a ring of c subunits in the membrane domain.

“F-type ATPase” is just another name for ATP synthase; letter “F” comes from “phosphorylation Factor”. F-ATPases are present in bacteria, mitochondria and chloroplasts. Their major function in most cases is ATP synthesis at the expense of the transmembrane electrochemical proton potential difference.

Subunits alpha and beta form the catalytic core in F(1). Rotation of the central stalk against the surrounding alpha(3)beta(3) subunits leads to hydrolysis of ATP in three separate catalytic sites on the beta subunits. Subunit alpha does not bear the catalytic high-affinity ATP-binding sites (By similarity).

The ATP synthase is a mitochondrial enzyme localized in the inner membrane, where it catalyzes the synthesis of ATP from ADP and phosphate, driven by a flux of protons across a gradient generated by electron transfer from the proton chemically positive to the negative side.

The E. coli Fo c ring just described has 12 c subunits. Thus, each proton that moves through Fo rotates the ring in 30o steps relative to the stationary components of ATP synthase (12 c’s x 30o = 360o).

about 130 revolutions per second

Krebs cycle

During ATP synthesis, rotation of the γ subunit causes sequential changes in the β subunits. A rotation of 120° changes the β subunit that binds ADP and Pi to a form with tightly bound ATP.

Understanding Which Metabolic Pathways Produce ATP in Glucose

• Glycolysis: 2 ATP.
• Krebs Cycle: 2 ATP.
• Oxidative Phosphorylation (Electron Transport Chain/Chemiosmosis): 28 ATP.
• Fermentation: 2 ATP.

Which energy system produces the least amount of ATP per substrate? The Citric Acid Cycle (directly) produces large quantities of ATP.

2 ATP

The NADH pulls the enzyme’s electrons to send through the electron transport chain. The electron transport chain pulls H+ ions through the chain. From the electron transport chain, the released hydrogen ions make ADP for an end result of 32 ATP.

Cells convert glucose to ATP in a process called cellular respiration. Cellular respiration: process of turning glucose into energy In the form of ATP. Before cellular respiration can begin, glucose must be refined into a form that is usable by the mitochondrion.

Step	ATP
Glycolysis	6
Citric Acid Cycle w/ 2 pyruvic acid	2 x 15 = 30 ATP
Net complete glucose	36 ATP