Electron transport chain (systems) or Oxidative Phosphorylation

steps of electron transport chain or oxidative phosphorylation2

What is the electron transport chain or systems:

The electron transport chain (system) is a chain or series of the carrier molecule. These molecules can oxidize and reduce other molecules. The other name of the electron transport chain is oxidative phosphorylation.
This chain occurs in a step by step process and electron are passed through this chain. This process causes the release of energy that is used to generate ATPs in chemiosmosis process.

 

Where the electron transport chain or systems does occur:

The Electron transport chain (system) occurs in the inner membrane of mitochondria of eukaryotic cells and plasma membrane of prokaryotic cells.

Types of carrier molecule:

There are three types of carrier molecules in the electron transport system.
These are:
• Flavoprotein
• Cytochrome
• Coenzyme Q or Ubiquinones

Flavoprotein contains a coenzyme called flavin that is the derivatives of riboflavin (Vitamin B2). This coenzyme can cause alternating oxidation and reduction.

A good example of a flavin coenzyme is flavin mononucleotide (FMN) or flavin adenine dinucleotide (FAD).

Electron transports occur since flavoprotein has a higher potentiality of reduction.

 

Cytochrome is the protein that has an iron-containing group (heme). This iron-containing group exists as an oxidized form (Fe3+) and reduced form (Fe2+ ).

There are several cytochromes in the electron transport chain (system). These cytochromes include cytochrome b (cyt b), cytochrome c1 (cyt c1), cytochrome c (cyt c), cytochrome a (cyt a), and cytochrome a3 (cyt a3).

 

Coenzyme Q or Ubiquinones. These coenzymes are ubiquitous in animals and most bacteria. The most common form of this coenzyme is ubiquinone 10.

 

The goal of electron transport chain or systems:

The electron transport chain or system varies in different organisms. And these various electron transport chain system has a different function and different goal in different organisms. Even a single bacterium can perform several types of electron transport chain (system).
But, all the electron transport chain (system) has the same basic goal in different organisms. The goal is that they release energy since electrons pass from higher energy compounds to lower energy compounds.

 

NOTE that electron transport syatem or oxidative phosphorylation is the third step of cellular respiration. The first step is glycolysis and the second step is the Krebs cycle.

Steps of E.T.S or Oxidative Phosphorylation:

1. Step 1 of the electron transport system:

The electron transport chain (system) in the mitochondria has been discussed here.
The first step of the electron transport chain (system) in the mitochondria involves the flow of electron from NADH to FMN. This step causes the passage of a proton (H+) and 2 electrons from NADH to FMN. This FMN also takes another proton from the surrounding aqueous medium.
This transfer causes the oxidation of NADH to NAD+ and the reduction of FMN to FMNH2.
It should be noted that NADH is a high energy compound that is oxidized to release energy.

 

steps of electron transport chain or oxidative phosphorylation
Figure 1: Electron Transport Chain. [This figure has been taken from MICROBIOLOGY: AN INTRODUCTION, TENTH EDITION by Gerard J. Tortora]

2. Step 2 of the electron transport system:

FMNH2 transfers two protons to other parts of the mitochondrial membrane and two electrons to ubiquinone (Q). This transfer causes the oxidation of FMNH2 to FMN. The ubiquinone (Q) also takes another proton from the surrounding aqueous medium and transfer it to the other part of the mitochondrial membrane.

3. Step 3 of the electron transport system:

Ubiquinone then transfers the electrons to cyt b, cyt c1, cyt c, cyt a, and cyt a3 and reduce these cytochromes as it takes up an electron. Cytochrome is also then oxidized by giving up electrons.
The last cytochrome is cyt a3, which transfers its electron to molecular oxygen (O2), as you know oxygen is the final electron acceptor in aerobic respiration.
By taking up this electron, oxygens become negatively charged and form H2O by taking up another proton from surrounding aqueous medium.

Finally, FMN and Q accept and release both electron and proton.
Other carriers like cytochromes only transfer electron in the electron transport chain or systems.

 

Read More on electron transport chain.

 

The enzymes involved in electron transport systems

• NADH dehydrogenase
• Succinate dehydrogenase
• Ubiquinone cytochrome c oxidoreductase
• Cytochrome oxidase

 

Inhibition of the electron transport chain or systems:

Several compounds interfere with the electron transport chain or systems such as

• Cyanide, Carbon monoxide inhibits cytochrome oxidase.

• Antimycin A blocks electron transfer from cytochrome b to cytochrome c1.

• Myxothiazol Rotenone, Piericidin A Amytal prevents electron transfer from Fe-S center to ubiquinone.

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