<< Chapter < Page Chapter >> Page >

Oxidative phosphorylation

In addition to substrate level phosphorylation, cells can generate ATP via an electron transport chain coupled to the proton dependent F0F1 ATPase. Such coupled systems require a membrane to both separate charge (electrical potential) and protons (chemical potential). This process is refereed, called the Chemiosmotic hypothesis was proposed by Peter Mitchell in 1961.

While we will discuss this in detail later, in essence oxidative phosphorylation works by taking a reduced high energy compound, such as NADH+H+ or FADH2, and transferring electrons in a series of redox reactions to other compounds. The energy that is release is then "captured" by the translocation of protons (H+) across the membrane. The net result is an "energize membrand" that separates charge, negative on the inside and positive on the outside (the electrical potential) and the separation of protons (chemical potential), protons concentration greater on the outside then inside of the membrane. The overall energized state of the membrane is then similar to a charged capacitor ready to do work. ATP generation occurs by the F0F1 membrane bound ATPase that translocates protons across the membrane discharging the chemical and electrical potentials with the simultaneous synthesis of ATP. For every three protons (H+) translocated, the F0F1ATPase can synthesize 1 ATP.

Finally, oxidative phosphorylation does NOT require oxygen to function. The word oxidative in this case is in reference to redox reactions driving the process. We are very familiar with aerobic respiration which uses molecular oxygen as the terminal electron acceptor in some electron transport chains but this is a subset of reactions. As we will see later, other electron transport chains can use other compounds besides molecular oxygen as a terminal electron acceptor, such as nitrate or nitrite.

Photophosphorylation

Finally, many organisms can convert the energy from sun light to chemical energy (ATP) which is half of the reactions used in photosynthesis; the other half being the conversion of CO2 to carbohydrates. In photosynthetic organisms, ATP and reducing power (production of NADPH+H+)is generated via a modified electron transport chain where the initial high energy electon(s) is derived from light energy instead of chemical energy from NADH+H+.

While we will discuss this in detail later, in essence oxidative phosphorylation works by taking a reduced high energy compound, such as NADH or FADH2, and transferring electrons in a series of red/ox reactions to other compounds. The energy that is release is then "captured" by the translocation of protons (H+) across the membrane. The net result is an "energize membrane" that separates charge, negative on the inside and positive on the outside (the electrical potential) and the separation of protons (chemical potential), protons concentration greater on the outside then inside of the membrane. The overall energized state of the membrane is then similar to a charged capacitor ready to do work. ATP generation occurs by the F0F1 membrane bound ATPase that translocates protons across the membrane discharging the chemical and electrical potentials with the simultaneous synthesis of ATP. For every three protons (H+) translocated, the F0F1ATPase can synthesize 1 ATP.

Section summary

ATP functions as the energy currency for cells. It allows the cell to store energy briefly and transport it within the cell to support endergonic chemical reactions. The structure of ATP is that of an RNA nucleotide with three phosphates attached. As ATP is used for energy, a phosphate group or two are detached, and either ADP or AMP is produced. Energy derived from glucose catabolism is used to convert ADP into ATP. When ATP is used in a reaction, the third phosphate is temporarily attached to a substrate in a process called phosphorylation. The two processes of ATP regeneration that are used in conjunction with glucose catabolism are substrate-level phosphorylation and oxidative phosphorylation through the process of chemiosmosis.

  • ATP

Insert paragraph text here.

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Ucd bis2a intro to biology v1.2. OpenStax CNX. Sep 22, 2015 Download for free at https://legacy.cnx.org/content/col11890/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Ucd bis2a intro to biology v1.2' conversation and receive update notifications?

Ask